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<hr>
<a name="Other-Built_002din-Functions-Provided-by-GCC"></a>
<h3 class="section">6.59 Other Built-in Functions Provided by GCC</h3>
<a name="index-built_002din-functions-1"></a>
<a name="index-_005f_005fbuiltin_005falloca"></a>
<a name="index-_005f_005fbuiltin_005falloca_005fwith_005falign"></a>
<a name="index-_005f_005fbuiltin_005falloca_005fwith_005falign_005fand_005fmax"></a>
<a name="index-_005f_005fbuiltin_005fcall_005fwith_005fstatic_005fchain"></a>
<a name="index-_005f_005fbuiltin_005fextend_005fpointer"></a>
<a name="index-_005f_005fbuiltin_005ffpclassify"></a>
<a name="index-_005f_005fbuiltin_005fhas_005fattribute"></a>
<a name="index-_005f_005fbuiltin_005fisfinite"></a>
<a name="index-_005f_005fbuiltin_005fisnormal"></a>
<a name="index-_005f_005fbuiltin_005fisgreater"></a>
<a name="index-_005f_005fbuiltin_005fisgreaterequal"></a>
<a name="index-_005f_005fbuiltin_005fisinf_005fsign"></a>
<a name="index-_005f_005fbuiltin_005fisless"></a>
<a name="index-_005f_005fbuiltin_005fislessequal"></a>
<a name="index-_005f_005fbuiltin_005fislessgreater"></a>
<a name="index-_005f_005fbuiltin_005fisunordered"></a>
<a name="index-_005f_005fbuiltin_005fobject_005fsize-2"></a>
<a name="index-_005f_005fbuiltin_005fpowi"></a>
<a name="index-_005f_005fbuiltin_005fpowif"></a>
<a name="index-_005f_005fbuiltin_005fpowil"></a>
<a name="index-_005f_005fbuiltin_005fspeculation_005fsafe_005fvalue"></a>
<a name="index-_005fExit"></a>
<a name="index-_005fexit"></a>
<a name="index-abort"></a>
<a name="index-abs"></a>
<a name="index-acos"></a>
<a name="index-acosf"></a>
<a name="index-acosh"></a>
<a name="index-acoshf"></a>
<a name="index-acoshl"></a>
<a name="index-acosl"></a>
<a name="index-alloca"></a>
<a name="index-asin"></a>
<a name="index-asinf"></a>
<a name="index-asinh"></a>
<a name="index-asinhf"></a>
<a name="index-asinhl"></a>
<a name="index-asinl"></a>
<a name="index-atan"></a>
<a name="index-atan2"></a>
<a name="index-atan2f"></a>
<a name="index-atan2l"></a>
<a name="index-atanf"></a>
<a name="index-atanh"></a>
<a name="index-atanhf"></a>
<a name="index-atanhl"></a>
<a name="index-atanl"></a>
<a name="index-bcmp"></a>
<a name="index-bzero"></a>
<a name="index-cabs"></a>
<a name="index-cabsf"></a>
<a name="index-cabsl"></a>
<a name="index-cacos"></a>
<a name="index-cacosf"></a>
<a name="index-cacosh"></a>
<a name="index-cacoshf"></a>
<a name="index-cacoshl"></a>
<a name="index-cacosl"></a>
<a name="index-calloc"></a>
<a name="index-carg"></a>
<a name="index-cargf"></a>
<a name="index-cargl"></a>
<a name="index-casin"></a>
<a name="index-casinf"></a>
<a name="index-casinh"></a>
<a name="index-casinhf"></a>
<a name="index-casinhl"></a>
<a name="index-casinl"></a>
<a name="index-catan"></a>
<a name="index-catanf"></a>
<a name="index-catanh"></a>
<a name="index-catanhf"></a>
<a name="index-catanhl"></a>
<a name="index-catanl"></a>
<a name="index-cbrt"></a>
<a name="index-cbrtf"></a>
<a name="index-cbrtl"></a>
<a name="index-ccos"></a>
<a name="index-ccosf"></a>
<a name="index-ccosh"></a>
<a name="index-ccoshf"></a>
<a name="index-ccoshl"></a>
<a name="index-ccosl"></a>
<a name="index-ceil"></a>
<a name="index-ceilf"></a>
<a name="index-ceill"></a>
<a name="index-cexp"></a>
<a name="index-cexpf"></a>
<a name="index-cexpl"></a>
<a name="index-cimag"></a>
<a name="index-cimagf"></a>
<a name="index-cimagl"></a>
<a name="index-clog"></a>
<a name="index-clogf"></a>
<a name="index-clogl"></a>
<a name="index-clog10"></a>
<a name="index-clog10f"></a>
<a name="index-clog10l"></a>
<a name="index-conj"></a>
<a name="index-conjf"></a>
<a name="index-conjl"></a>
<a name="index-copysign"></a>
<a name="index-copysignf"></a>
<a name="index-copysignl"></a>
<a name="index-cos"></a>
<a name="index-cosf"></a>
<a name="index-cosh"></a>
<a name="index-coshf"></a>
<a name="index-coshl"></a>
<a name="index-cosl"></a>
<a name="index-cpow"></a>
<a name="index-cpowf"></a>
<a name="index-cpowl"></a>
<a name="index-cproj"></a>
<a name="index-cprojf"></a>
<a name="index-cprojl"></a>
<a name="index-creal"></a>
<a name="index-crealf"></a>
<a name="index-creall"></a>
<a name="index-csin"></a>
<a name="index-csinf"></a>
<a name="index-csinh"></a>
<a name="index-csinhf"></a>
<a name="index-csinhl"></a>
<a name="index-csinl"></a>
<a name="index-csqrt"></a>
<a name="index-csqrtf"></a>
<a name="index-csqrtl"></a>
<a name="index-ctan"></a>
<a name="index-ctanf"></a>
<a name="index-ctanh"></a>
<a name="index-ctanhf"></a>
<a name="index-ctanhl"></a>
<a name="index-ctanl"></a>
<a name="index-dcgettext"></a>
<a name="index-dgettext"></a>
<a name="index-drem"></a>
<a name="index-dremf"></a>
<a name="index-dreml"></a>
<a name="index-erf"></a>
<a name="index-erfc"></a>
<a name="index-erfcf"></a>
<a name="index-erfcl"></a>
<a name="index-erff"></a>
<a name="index-erfl"></a>
<a name="index-exit"></a>
<a name="index-exp"></a>
<a name="index-exp10"></a>
<a name="index-exp10f"></a>
<a name="index-exp10l"></a>
<a name="index-exp2"></a>
<a name="index-exp2f"></a>
<a name="index-exp2l"></a>
<a name="index-expf"></a>
<a name="index-expl"></a>
<a name="index-expm1"></a>
<a name="index-expm1f"></a>
<a name="index-expm1l"></a>
<a name="index-fabs"></a>
<a name="index-fabsf"></a>
<a name="index-fabsl"></a>
<a name="index-fdim"></a>
<a name="index-fdimf"></a>
<a name="index-fdiml"></a>
<a name="index-ffs"></a>
<a name="index-floor"></a>
<a name="index-floorf"></a>
<a name="index-floorl"></a>
<a name="index-fma"></a>
<a name="index-fmaf"></a>
<a name="index-fmal"></a>
<a name="index-fmax"></a>
<a name="index-fmaxf"></a>
<a name="index-fmaxl"></a>
<a name="index-fmin"></a>
<a name="index-fminf"></a>
<a name="index-fminl"></a>
<a name="index-fmod"></a>
<a name="index-fmodf"></a>
<a name="index-fmodl"></a>
<a name="index-fprintf"></a>
<a name="index-fprintf_005funlocked"></a>
<a name="index-fputs"></a>
<a name="index-fputs_005funlocked"></a>
<a name="index-free"></a>
<a name="index-frexp"></a>
<a name="index-frexpf"></a>
<a name="index-frexpl"></a>
<a name="index-fscanf"></a>
<a name="index-gamma"></a>
<a name="index-gammaf"></a>
<a name="index-gammal"></a>
<a name="index-gamma_005fr"></a>
<a name="index-gammaf_005fr"></a>
<a name="index-gammal_005fr"></a>
<a name="index-gettext"></a>
<a name="index-hypot"></a>
<a name="index-hypotf"></a>
<a name="index-hypotl"></a>
<a name="index-ilogb"></a>
<a name="index-ilogbf"></a>
<a name="index-ilogbl"></a>
<a name="index-imaxabs"></a>
<a name="index-index"></a>
<a name="index-isalnum"></a>
<a name="index-isalpha"></a>
<a name="index-isascii"></a>
<a name="index-isblank"></a>
<a name="index-iscntrl"></a>
<a name="index-isdigit"></a>
<a name="index-isgraph"></a>
<a name="index-islower"></a>
<a name="index-isprint"></a>
<a name="index-ispunct"></a>
<a name="index-isspace"></a>
<a name="index-isupper"></a>
<a name="index-iswalnum"></a>
<a name="index-iswalpha"></a>
<a name="index-iswblank"></a>
<a name="index-iswcntrl"></a>
<a name="index-iswdigit"></a>
<a name="index-iswgraph"></a>
<a name="index-iswlower"></a>
<a name="index-iswprint"></a>
<a name="index-iswpunct"></a>
<a name="index-iswspace"></a>
<a name="index-iswupper"></a>
<a name="index-iswxdigit"></a>
<a name="index-isxdigit"></a>
<a name="index-j0"></a>
<a name="index-j0f"></a>
<a name="index-j0l"></a>
<a name="index-j1"></a>
<a name="index-j1f"></a>
<a name="index-j1l"></a>
<a name="index-jn"></a>
<a name="index-jnf"></a>
<a name="index-jnl"></a>
<a name="index-labs"></a>
<a name="index-ldexp"></a>
<a name="index-ldexpf"></a>
<a name="index-ldexpl"></a>
<a name="index-lgamma"></a>
<a name="index-lgammaf"></a>
<a name="index-lgammal"></a>
<a name="index-lgamma_005fr"></a>
<a name="index-lgammaf_005fr"></a>
<a name="index-lgammal_005fr"></a>
<a name="index-llabs"></a>
<a name="index-llrint"></a>
<a name="index-llrintf"></a>
<a name="index-llrintl"></a>
<a name="index-llround"></a>
<a name="index-llroundf"></a>
<a name="index-llroundl"></a>
<a name="index-log"></a>
<a name="index-log10"></a>
<a name="index-log10f"></a>
<a name="index-log10l"></a>
<a name="index-log1p"></a>
<a name="index-log1pf"></a>
<a name="index-log1pl"></a>
<a name="index-log2"></a>
<a name="index-log2f"></a>
<a name="index-log2l"></a>
<a name="index-logb"></a>
<a name="index-logbf"></a>
<a name="index-logbl"></a>
<a name="index-logf"></a>
<a name="index-logl"></a>
<a name="index-lrint"></a>
<a name="index-lrintf"></a>
<a name="index-lrintl"></a>
<a name="index-lround"></a>
<a name="index-lroundf"></a>
<a name="index-lroundl"></a>
<a name="index-malloc"></a>
<a name="index-memchr"></a>
<a name="index-memcmp"></a>
<a name="index-memcpy"></a>
<a name="index-mempcpy"></a>
<a name="index-memset"></a>
<a name="index-modf"></a>
<a name="index-modff"></a>
<a name="index-modfl"></a>
<a name="index-nearbyint"></a>
<a name="index-nearbyintf"></a>
<a name="index-nearbyintl"></a>
<a name="index-nextafter"></a>
<a name="index-nextafterf"></a>
<a name="index-nextafterl"></a>
<a name="index-nexttoward"></a>
<a name="index-nexttowardf"></a>
<a name="index-nexttowardl"></a>
<a name="index-pow"></a>
<a name="index-pow10"></a>
<a name="index-pow10f"></a>
<a name="index-pow10l"></a>
<a name="index-powf"></a>
<a name="index-powl"></a>
<a name="index-printf"></a>
<a name="index-printf_005funlocked"></a>
<a name="index-putchar"></a>
<a name="index-puts"></a>
<a name="index-realloc"></a>
<a name="index-remainder"></a>
<a name="index-remainderf"></a>
<a name="index-remainderl"></a>
<a name="index-remquo"></a>
<a name="index-remquof"></a>
<a name="index-remquol"></a>
<a name="index-rindex"></a>
<a name="index-rint"></a>
<a name="index-rintf"></a>
<a name="index-rintl"></a>
<a name="index-round"></a>
<a name="index-roundf"></a>
<a name="index-roundl"></a>
<a name="index-scalb"></a>
<a name="index-scalbf"></a>
<a name="index-scalbl"></a>
<a name="index-scalbln"></a>
<a name="index-scalblnf"></a>
<a name="index-scalblnf-1"></a>
<a name="index-scalbn"></a>
<a name="index-scalbnf"></a>
<a name="index-scanfnl"></a>
<a name="index-signbit"></a>
<a name="index-signbitf"></a>
<a name="index-signbitl"></a>
<a name="index-signbitd32"></a>
<a name="index-signbitd64"></a>
<a name="index-signbitd128"></a>
<a name="index-significand"></a>
<a name="index-significandf"></a>
<a name="index-significandl"></a>
<a name="index-sin"></a>
<a name="index-sincos"></a>
<a name="index-sincosf"></a>
<a name="index-sincosl"></a>
<a name="index-sinf"></a>
<a name="index-sinh"></a>
<a name="index-sinhf"></a>
<a name="index-sinhl"></a>
<a name="index-sinl"></a>
<a name="index-snprintf"></a>
<a name="index-sprintf"></a>
<a name="index-sqrt"></a>
<a name="index-sqrtf"></a>
<a name="index-sqrtl"></a>
<a name="index-sscanf"></a>
<a name="index-stpcpy"></a>
<a name="index-stpncpy"></a>
<a name="index-strcasecmp"></a>
<a name="index-strcat"></a>
<a name="index-strchr"></a>
<a name="index-strcmp"></a>
<a name="index-strcpy"></a>
<a name="index-strcspn"></a>
<a name="index-strdup"></a>
<a name="index-strfmon"></a>
<a name="index-strftime"></a>
<a name="index-strlen"></a>
<a name="index-strncasecmp"></a>
<a name="index-strncat"></a>
<a name="index-strncmp"></a>
<a name="index-strncpy"></a>
<a name="index-strndup"></a>
<a name="index-strnlen"></a>
<a name="index-strpbrk"></a>
<a name="index-strrchr"></a>
<a name="index-strspn"></a>
<a name="index-strstr"></a>
<a name="index-tan"></a>
<a name="index-tanf"></a>
<a name="index-tanh"></a>
<a name="index-tanhf"></a>
<a name="index-tanhl"></a>
<a name="index-tanl"></a>
<a name="index-tgamma"></a>
<a name="index-tgammaf"></a>
<a name="index-tgammal"></a>
<a name="index-toascii"></a>
<a name="index-tolower"></a>
<a name="index-toupper"></a>
<a name="index-towlower"></a>
<a name="index-towupper"></a>
<a name="index-trunc"></a>
<a name="index-truncf"></a>
<a name="index-truncl"></a>
<a name="index-vfprintf"></a>
<a name="index-vfscanf"></a>
<a name="index-vprintf"></a>
<a name="index-vscanf"></a>
<a name="index-vsnprintf"></a>
<a name="index-vsprintf"></a>
<a name="index-vsscanf"></a>
<a name="index-y0"></a>
<a name="index-y0f"></a>
<a name="index-y0l"></a>
<a name="index-y1"></a>
<a name="index-y1f"></a>
<a name="index-y1l"></a>
<a name="index-yn"></a>
<a name="index-ynf"></a>
<a name="index-ynl"></a>

<p>GCC provides a large number of built-in functions other than the ones
mentioned above.  Some of these are for internal use in the processing
of exceptions or variable-length argument lists and are not
documented here because they may change from time to time; we do not
recommend general use of these functions.
</p>
<p>The remaining functions are provided for optimization purposes.
</p>
<p>With the exception of built-ins that have library equivalents such as
the standard C library functions discussed below, or that expand to
library calls, GCC built-in functions are always expanded inline and
thus do not have corresponding entry points and their address cannot
be obtained.  Attempting to use them in an expression other than
a function call results in a compile-time error.
</p>
<a name="index-fno_002dbuiltin-3"></a>
<p>GCC includes built-in versions of many of the functions in the standard
C library.  These functions come in two forms: one whose names start with
the <code>__builtin_</code> prefix, and the other without.  Both forms have the
same type (including prototype), the same address (when their address is
taken), and the same meaning as the C library functions even if you specify
the <samp>-fno-builtin</samp> option see <a href="C-Dialect-Options.html#C-Dialect-Options">C Dialect Options</a>).  Many of these
functions are only optimized in certain cases; if they are not optimized in
a particular case, a call to the library function is emitted.
</p>
<a name="index-ansi-2"></a>
<a name="index-std-2"></a>
<p>Outside strict ISO C mode (<samp>-ansi</samp>, <samp>-std=c90</samp>,
<samp>-std=c99</samp> or <samp>-std=c11</samp>), the functions
<code>_exit</code>, <code>alloca</code>, <code>bcmp</code>, <code>bzero</code>,
<code>dcgettext</code>, <code>dgettext</code>, <code>dremf</code>, <code>dreml</code>,
<code>drem</code>, <code>exp10f</code>, <code>exp10l</code>, <code>exp10</code>, <code>ffsll</code>,
<code>ffsl</code>, <code>ffs</code>, <code>fprintf_unlocked</code>,
<code>fputs_unlocked</code>, <code>gammaf</code>, <code>gammal</code>, <code>gamma</code>,
<code>gammaf_r</code>, <code>gammal_r</code>, <code>gamma_r</code>, <code>gettext</code>,
<code>index</code>, <code>isascii</code>, <code>j0f</code>, <code>j0l</code>, <code>j0</code>,
<code>j1f</code>, <code>j1l</code>, <code>j1</code>, <code>jnf</code>, <code>jnl</code>, <code>jn</code>,
<code>lgammaf_r</code>, <code>lgammal_r</code>, <code>lgamma_r</code>, <code>mempcpy</code>,
<code>pow10f</code>, <code>pow10l</code>, <code>pow10</code>, <code>printf_unlocked</code>,
<code>rindex</code>, <code>roundeven</code>, <code>roundevenf</code>, <code>roudnevenl</code>,
<code>scalbf</code>, <code>scalbl</code>, <code>scalb</code>,
<code>signbit</code>, <code>signbitf</code>, <code>signbitl</code>, <code>signbitd32</code>,
<code>signbitd64</code>, <code>signbitd128</code>, <code>significandf</code>,
<code>significandl</code>, <code>significand</code>, <code>sincosf</code>,
<code>sincosl</code>, <code>sincos</code>, <code>stpcpy</code>, <code>stpncpy</code>,
<code>strcasecmp</code>, <code>strdup</code>, <code>strfmon</code>, <code>strncasecmp</code>,
<code>strndup</code>, <code>strnlen</code>, <code>toascii</code>, <code>y0f</code>, <code>y0l</code>,
<code>y0</code>, <code>y1f</code>, <code>y1l</code>, <code>y1</code>, <code>ynf</code>, <code>ynl</code> and
<code>yn</code>
may be handled as built-in functions.
All these functions have corresponding versions
prefixed with <code>__builtin_</code>, which may be used even in strict C90
mode.
</p>
<p>The ISO C99 functions
<code>_Exit</code>, <code>acoshf</code>, <code>acoshl</code>, <code>acosh</code>, <code>asinhf</code>,
<code>asinhl</code>, <code>asinh</code>, <code>atanhf</code>, <code>atanhl</code>, <code>atanh</code>,
<code>cabsf</code>, <code>cabsl</code>, <code>cabs</code>, <code>cacosf</code>, <code>cacoshf</code>,
<code>cacoshl</code>, <code>cacosh</code>, <code>cacosl</code>, <code>cacos</code>,
<code>cargf</code>, <code>cargl</code>, <code>carg</code>, <code>casinf</code>, <code>casinhf</code>,
<code>casinhl</code>, <code>casinh</code>, <code>casinl</code>, <code>casin</code>,
<code>catanf</code>, <code>catanhf</code>, <code>catanhl</code>, <code>catanh</code>,
<code>catanl</code>, <code>catan</code>, <code>cbrtf</code>, <code>cbrtl</code>, <code>cbrt</code>,
<code>ccosf</code>, <code>ccoshf</code>, <code>ccoshl</code>, <code>ccosh</code>, <code>ccosl</code>,
<code>ccos</code>, <code>cexpf</code>, <code>cexpl</code>, <code>cexp</code>, <code>cimagf</code>,
<code>cimagl</code>, <code>cimag</code>, <code>clogf</code>, <code>clogl</code>, <code>clog</code>,
<code>conjf</code>, <code>conjl</code>, <code>conj</code>, <code>copysignf</code>, <code>copysignl</code>,
<code>copysign</code>, <code>cpowf</code>, <code>cpowl</code>, <code>cpow</code>, <code>cprojf</code>,
<code>cprojl</code>, <code>cproj</code>, <code>crealf</code>, <code>creall</code>, <code>creal</code>,
<code>csinf</code>, <code>csinhf</code>, <code>csinhl</code>, <code>csinh</code>, <code>csinl</code>,
<code>csin</code>, <code>csqrtf</code>, <code>csqrtl</code>, <code>csqrt</code>, <code>ctanf</code>,
<code>ctanhf</code>, <code>ctanhl</code>, <code>ctanh</code>, <code>ctanl</code>, <code>ctan</code>,
<code>erfcf</code>, <code>erfcl</code>, <code>erfc</code>, <code>erff</code>, <code>erfl</code>,
<code>erf</code>, <code>exp2f</code>, <code>exp2l</code>, <code>exp2</code>, <code>expm1f</code>,
<code>expm1l</code>, <code>expm1</code>, <code>fdimf</code>, <code>fdiml</code>, <code>fdim</code>,
<code>fmaf</code>, <code>fmal</code>, <code>fmaxf</code>, <code>fmaxl</code>, <code>fmax</code>,
<code>fma</code>, <code>fminf</code>, <code>fminl</code>, <code>fmin</code>, <code>hypotf</code>,
<code>hypotl</code>, <code>hypot</code>, <code>ilogbf</code>, <code>ilogbl</code>, <code>ilogb</code>,
<code>imaxabs</code>, <code>isblank</code>, <code>iswblank</code>, <code>lgammaf</code>,
<code>lgammal</code>, <code>lgamma</code>, <code>llabs</code>, <code>llrintf</code>, <code>llrintl</code>,
<code>llrint</code>, <code>llroundf</code>, <code>llroundl</code>, <code>llround</code>,
<code>log1pf</code>, <code>log1pl</code>, <code>log1p</code>, <code>log2f</code>, <code>log2l</code>,
<code>log2</code>, <code>logbf</code>, <code>logbl</code>, <code>logb</code>, <code>lrintf</code>,
<code>lrintl</code>, <code>lrint</code>, <code>lroundf</code>, <code>lroundl</code>,
<code>lround</code>, <code>nearbyintf</code>, <code>nearbyintl</code>, <code>nearbyint</code>,
<code>nextafterf</code>, <code>nextafterl</code>, <code>nextafter</code>,
<code>nexttowardf</code>, <code>nexttowardl</code>, <code>nexttoward</code>,
<code>remainderf</code>, <code>remainderl</code>, <code>remainder</code>, <code>remquof</code>,
<code>remquol</code>, <code>remquo</code>, <code>rintf</code>, <code>rintl</code>, <code>rint</code>,
<code>roundf</code>, <code>roundl</code>, <code>round</code>, <code>scalblnf</code>,
<code>scalblnl</code>, <code>scalbln</code>, <code>scalbnf</code>, <code>scalbnl</code>,
<code>scalbn</code>, <code>snprintf</code>, <code>tgammaf</code>, <code>tgammal</code>,
<code>tgamma</code>, <code>truncf</code>, <code>truncl</code>, <code>trunc</code>,
<code>vfscanf</code>, <code>vscanf</code>, <code>vsnprintf</code> and <code>vsscanf</code>
are handled as built-in functions
except in strict ISO C90 mode (<samp>-ansi</samp> or <samp>-std=c90</samp>).
</p>
<p>There are also built-in versions of the ISO C99 functions
<code>acosf</code>, <code>acosl</code>, <code>asinf</code>, <code>asinl</code>, <code>atan2f</code>,
<code>atan2l</code>, <code>atanf</code>, <code>atanl</code>, <code>ceilf</code>, <code>ceill</code>,
<code>cosf</code>, <code>coshf</code>, <code>coshl</code>, <code>cosl</code>, <code>expf</code>,
<code>expl</code>, <code>fabsf</code>, <code>fabsl</code>, <code>floorf</code>, <code>floorl</code>,
<code>fmodf</code>, <code>fmodl</code>, <code>frexpf</code>, <code>frexpl</code>, <code>ldexpf</code>,
<code>ldexpl</code>, <code>log10f</code>, <code>log10l</code>, <code>logf</code>, <code>logl</code>,
<code>modfl</code>, <code>modf</code>, <code>powf</code>, <code>powl</code>, <code>sinf</code>,
<code>sinhf</code>, <code>sinhl</code>, <code>sinl</code>, <code>sqrtf</code>, <code>sqrtl</code>,
<code>tanf</code>, <code>tanhf</code>, <code>tanhl</code> and <code>tanl</code>
that are recognized in any mode since ISO C90 reserves these names for
the purpose to which ISO C99 puts them.  All these functions have
corresponding versions prefixed with <code>__builtin_</code>.
</p>
<p>There are also built-in functions <code>__builtin_fabsf<var>n</var></code>,
<code>__builtin_fabsf<var>n</var>x</code>, <code>__builtin_copysignf<var>n</var></code> and
<code>__builtin_copysignf<var>n</var>x</code>, corresponding to the TS 18661-3
functions <code>fabsf<var>n</var></code>, <code>fabsf<var>n</var>x</code>,
<code>copysignf<var>n</var></code> and <code>copysignf<var>n</var>x</code>, for supported
types <code>_Float<var>n</var></code> and <code>_Float<var>n</var>x</code>.
</p>
<p>There are also GNU extension functions <code>clog10</code>, <code>clog10f</code> and
<code>clog10l</code> which names are reserved by ISO C99 for future use.
All these functions have versions prefixed with <code>__builtin_</code>.
</p>
<p>The ISO C94 functions
<code>iswalnum</code>, <code>iswalpha</code>, <code>iswcntrl</code>, <code>iswdigit</code>,
<code>iswgraph</code>, <code>iswlower</code>, <code>iswprint</code>, <code>iswpunct</code>,
<code>iswspace</code>, <code>iswupper</code>, <code>iswxdigit</code>, <code>towlower</code> and
<code>towupper</code>
are handled as built-in functions
except in strict ISO C90 mode (<samp>-ansi</samp> or <samp>-std=c90</samp>).
</p>
<p>The ISO C90 functions
<code>abort</code>, <code>abs</code>, <code>acos</code>, <code>asin</code>, <code>atan2</code>,
<code>atan</code>, <code>calloc</code>, <code>ceil</code>, <code>cosh</code>, <code>cos</code>,
<code>exit</code>, <code>exp</code>, <code>fabs</code>, <code>floor</code>, <code>fmod</code>,
<code>fprintf</code>, <code>fputs</code>, <code>free</code>, <code>frexp</code>, <code>fscanf</code>,
<code>isalnum</code>, <code>isalpha</code>, <code>iscntrl</code>, <code>isdigit</code>,
<code>isgraph</code>, <code>islower</code>, <code>isprint</code>, <code>ispunct</code>,
<code>isspace</code>, <code>isupper</code>, <code>isxdigit</code>, <code>tolower</code>,
<code>toupper</code>, <code>labs</code>, <code>ldexp</code>, <code>log10</code>, <code>log</code>,
<code>malloc</code>, <code>memchr</code>, <code>memcmp</code>, <code>memcpy</code>,
<code>memset</code>, <code>modf</code>, <code>pow</code>, <code>printf</code>, <code>putchar</code>,
<code>puts</code>, <code>realloc</code>, <code>scanf</code>, <code>sinh</code>, <code>sin</code>,
<code>snprintf</code>, <code>sprintf</code>, <code>sqrt</code>, <code>sscanf</code>, <code>strcat</code>,
<code>strchr</code>, <code>strcmp</code>, <code>strcpy</code>, <code>strcspn</code>,
<code>strlen</code>, <code>strncat</code>, <code>strncmp</code>, <code>strncpy</code>,
<code>strpbrk</code>, <code>strrchr</code>, <code>strspn</code>, <code>strstr</code>,
<code>tanh</code>, <code>tan</code>, <code>vfprintf</code>, <code>vprintf</code> and <code>vsprintf</code>
are all recognized as built-in functions unless
<samp>-fno-builtin</samp> is specified (or <samp>-fno-builtin-<var>function</var></samp>
is specified for an individual function).  All of these functions have
corresponding versions prefixed with <code>__builtin_</code>.
</p>
<p>GCC provides built-in versions of the ISO C99 floating-point comparison
macros that avoid raising exceptions for unordered operands.  They have
the same names as the standard macros ( <code>isgreater</code>,
<code>isgreaterequal</code>, <code>isless</code>, <code>islessequal</code>,
<code>islessgreater</code>, and <code>isunordered</code>) , with <code>__builtin_</code>
prefixed.  We intend for a library implementor to be able to simply
<code>#define</code> each standard macro to its built-in equivalent.
In the same fashion, GCC provides <code>fpclassify</code>, <code>isfinite</code>,
<code>isinf_sign</code>, <code>isnormal</code> and <code>signbit</code> built-ins used with
<code>__builtin_</code> prefixed.  The <code>isinf</code> and <code>isnan</code>
built-in functions appear both with and without the <code>__builtin_</code> prefix.
</p>
<dl>
<dt><a name="index-_002a_005f_005fbuiltin_005falloca"></a>Built-in Function: <em>void</em> <strong>*__builtin_alloca</strong> <em>(size_t size)</em></dt>
<dd><p>The <code>__builtin_alloca</code> function must be called at block scope.
The function allocates an object <var>size</var> bytes large on the stack
of the calling function.  The object is aligned on the default stack
alignment boundary for the target determined by the
<code>__BIGGEST_ALIGNMENT__</code> macro.  The <code>__builtin_alloca</code>
function returns a pointer to the first byte of the allocated object.
The lifetime of the allocated object ends just before the calling
function returns to its caller.   This is so even when
<code>__builtin_alloca</code> is called within a nested block.
</p>
<p>For example, the following function allocates eight objects of <code>n</code>
bytes each on the stack, storing a pointer to each in consecutive elements
of the array <code>a</code>.  It then passes the array to function <code>g</code>
which can safely use the storage pointed to by each of the array elements.
</p>
<div class="smallexample">
<pre class="smallexample">void f (unsigned n)
{
  void *a [8];
  for (int i = 0; i != 8; ++i)
    a [i] = __builtin_alloca (n);

  g (a, n);   // <span class="roman">safe</span>
}
</pre></div>

<p>Since the <code>__builtin_alloca</code> function doesn&rsquo;t validate its argument
it is the responsibility of its caller to make sure the argument doesn&rsquo;t
cause it to exceed the stack size limit.
The <code>__builtin_alloca</code> function is provided to make it possible to
allocate on the stack arrays of bytes with an upper bound that may be
computed at run time.  Since C99 Variable Length Arrays offer
similar functionality under a portable, more convenient, and safer
interface they are recommended instead, in both C99 and C++ programs
where GCC provides them as an extension.
See <a href="Variable-Length.html#Variable-Length">Variable Length</a>, for details.
</p>
</dd></dl>

<dl>
<dt><a name="index-_002a_005f_005fbuiltin_005falloca_005fwith_005falign"></a>Built-in Function: <em>void</em> <strong>*__builtin_alloca_with_align</strong> <em>(size_t size, size_t alignment)</em></dt>
<dd><p>The <code>__builtin_alloca_with_align</code> function must be called at block
scope.  The function allocates an object <var>size</var> bytes large on
the stack of the calling function.  The allocated object is aligned on
the boundary specified by the argument <var>alignment</var> whose unit is given
in bits (not bytes).  The <var>size</var> argument must be positive and not
exceed the stack size limit.  The <var>alignment</var> argument must be a constant
integer expression that evaluates to a power of 2 greater than or equal to
<code>CHAR_BIT</code> and less than some unspecified maximum.  Invocations
with other values are rejected with an error indicating the valid bounds.
The function returns a pointer to the first byte of the allocated object.
The lifetime of the allocated object ends at the end of the block in which
the function was called.  The allocated storage is released no later than
just before the calling function returns to its caller, but may be released
at the end of the block in which the function was called.
</p>
<p>For example, in the following function the call to <code>g</code> is unsafe
because when <code>overalign</code> is non-zero, the space allocated by
<code>__builtin_alloca_with_align</code> may have been released at the end
of the <code>if</code> statement in which it was called.
</p>
<div class="smallexample">
<pre class="smallexample">void f (unsigned n, bool overalign)
{
  void *p;
  if (overalign)
    p = __builtin_alloca_with_align (n, 64 /* bits */);
  else
    p = __builtin_alloc (n);

  g (p, n);   // <span class="roman">unsafe</span>
}
</pre></div>

<p>Since the <code>__builtin_alloca_with_align</code> function doesn&rsquo;t validate its
<var>size</var> argument it is the responsibility of its caller to make sure
the argument doesn&rsquo;t cause it to exceed the stack size limit.
The <code>__builtin_alloca_with_align</code> function is provided to make
it possible to allocate on the stack overaligned arrays of bytes with
an upper bound that may be computed at run time.  Since C99
Variable Length Arrays offer the same functionality under
a portable, more convenient, and safer interface they are recommended
instead, in both C99 and C++ programs where GCC provides them as
an extension.  See <a href="Variable-Length.html#Variable-Length">Variable Length</a>, for details.
</p>
</dd></dl>

<dl>
<dt><a name="index-_002a_005f_005fbuiltin_005falloca_005fwith_005falign_005fand_005fmax"></a>Built-in Function: <em>void</em> <strong>*__builtin_alloca_with_align_and_max</strong> <em>(size_t size, size_t alignment, size_t max_size)</em></dt>
<dd><p>Similar to <code>__builtin_alloca_with_align</code> but takes an extra argument
specifying an upper bound for <var>size</var> in case its value cannot be computed
at compile time, for use by <samp>-fstack-usage</samp>, <samp>-Wstack-usage</samp>
and <samp>-Walloca-larger-than</samp>.  <var>max_size</var> must be a constant integer
expression, it has no effect on code generation and no attempt is made to
check its compatibility with <var>size</var>.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fhas_005fattribute-1"></a>Built-in Function: <em>bool</em> <strong>__builtin_has_attribute</strong> <em>(<var>type-or-expression</var>, <var>attribute</var>)</em></dt>
<dd><p>The <code>__builtin_has_attribute</code> function evaluates to an integer constant
expression equal to <code>true</code> if the symbol or type referenced by
the <var>type-or-expression</var> argument has been declared with
the <var>attribute</var> referenced by the second argument.  For
an <var>type-or-expression</var> argument that does not reference a symbol,
since attributes do not apply to expressions the built-in consider
the type of the argument.  Neither argument is evaluated.
The <var>type-or-expression</var> argument is subject to the same
restrictions as the argument to <code>typeof</code> (see <a href="Typeof.html#Typeof">Typeof</a>).  The
<var>attribute</var> argument is an attribute name optionally followed by
a comma-separated list of arguments enclosed in parentheses.  Both forms
of attribute names&mdash;with and without double leading and trailing
underscores&mdash;are recognized.  See <a href="Attribute-Syntax.html#Attribute-Syntax">Attribute Syntax</a>, for details.
When no attribute arguments are specified for an attribute that expects
one or more arguments the function returns <code>true</code> if
<var>type-or-expression</var> has been declared with the attribute regardless
of the attribute argument values.  Arguments provided for an attribute
that expects some are validated and matched up to the provided number.
The function returns <code>true</code> if all provided arguments match.  For
example, the first call to the function below evaluates to <code>true</code>
because <code>x</code> is declared with the <code>aligned</code> attribute but
the second call evaluates to <code>false</code> because <code>x</code> is declared
<code>aligned (8)</code> and not <code>aligned (4)</code>.
</p>
<div class="smallexample">
<pre class="smallexample">__attribute__ ((aligned (8))) int x;
_Static_assert (__builtin_has_attribute (x, aligned), &quot;aligned&quot;);
_Static_assert (!__builtin_has_attribute (x, aligned (4)), &quot;aligned (4)&quot;);
</pre></div>

<p>Due to a limitation the <code>__builtin_has_attribute</code> function returns
<code>false</code> for the <code>mode</code> attribute even if the type or variable
referenced by the <var>type-or-expression</var> argument was declared with one.
The function is also not supported with labels, and in C with enumerators.
</p>
<p>Note that unlike the <code>__has_attribute</code> preprocessor operator which
is suitable for use in <code>#if</code> preprocessing directives
<code>__builtin_has_attribute</code> is an intrinsic function that is not
recognized in such contexts.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fspeculation_005fsafe_005fvalue-1"></a>Built-in Function: <em><var>type</var></em> <strong>__builtin_speculation_safe_value</strong> <em>(<var>type</var> val, <var>type</var> failval)</em></dt>
<dd>
<p>This built-in function can be used to help mitigate against unsafe
speculative execution.  <var>type</var> may be any integral type or any
pointer type.
</p>
<ol>
<li> If the CPU is not speculatively executing the code, then <var>val</var>
is returned.
</li><li> If the CPU is executing speculatively then either:
<ul>
<li> The function may cause execution to pause until it is known that the
code is no-longer being executed speculatively (in which case
<var>val</var> can be returned, as above); or
</li><li> The function may use target-dependent speculation tracking state to cause
<var>failval</var> to be returned when it is known that speculative
execution has incorrectly predicted a conditional branch operation.
</li></ul>
</li></ol>

<p>The second argument, <var>failval</var>, is optional and defaults to zero
if omitted.
</p>
<p>GCC defines the preprocessor macro
<code>__HAVE_BUILTIN_SPECULATION_SAFE_VALUE</code> for targets that have been
updated to support this builtin.
</p>
<p>The built-in function can be used where a variable appears to be used in a
safe way, but the CPU, due to speculative execution may temporarily ignore
the bounds checks.  Consider, for example, the following function:
</p>
<div class="smallexample">
<pre class="smallexample">int array[500];
int f (unsigned untrusted_index)
{
  if (untrusted_index &lt; 500)
    return array[untrusted_index];
  return 0;
}
</pre></div>

<p>If the function is called repeatedly with <code>untrusted_index</code> less
than the limit of 500, then a branch predictor will learn that the
block of code that returns a value stored in <code>array</code> will be
executed.  If the function is subsequently called with an
out-of-range value it will still try to execute that block of code
first until the CPU determines that the prediction was incorrect
(the CPU will unwind any incorrect operations at that point).
However, depending on how the result of the function is used, it might be
possible to leave traces in the cache that can reveal what was stored
at the out-of-bounds location.  The built-in function can be used to
provide some protection against leaking data in this way by changing
the code to:
</p>
<div class="smallexample">
<pre class="smallexample">int array[500];
int f (unsigned untrusted_index)
{
  if (untrusted_index &lt; 500)
    return array[__builtin_speculation_safe_value (untrusted_index)];
  return 0;
}
</pre></div>

<p>The built-in function will either cause execution to stall until the
conditional branch has been fully resolved, or it may permit
speculative execution to continue, but using 0 instead of
<code>untrusted_value</code> if that exceeds the limit.
</p>
<p>If accessing any memory location is potentially unsafe when speculative
execution is incorrect, then the code can be rewritten as
</p>
<div class="smallexample">
<pre class="smallexample">int array[500];
int f (unsigned untrusted_index)
{
  if (untrusted_index &lt; 500)
    return *__builtin_speculation_safe_value (&amp;array[untrusted_index], NULL);
  return 0;
}
</pre></div>

<p>which will cause a <code>NULL</code> pointer to be used for the unsafe case.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005ftypes_005fcompatible_005fp"></a>Built-in Function: <em>int</em> <strong>__builtin_types_compatible_p</strong> <em>(<var>type1</var>, <var>type2</var>)</em></dt>
<dd>
<p>You can use the built-in function <code>__builtin_types_compatible_p</code> to
determine whether two types are the same.
</p>
<p>This built-in function returns 1 if the unqualified versions of the
types <var>type1</var> and <var>type2</var> (which are types, not expressions) are
compatible, 0 otherwise.  The result of this built-in function can be
used in integer constant expressions.
</p>
<p>This built-in function ignores top level qualifiers (e.g., <code>const</code>,
<code>volatile</code>).  For example, <code>int</code> is equivalent to <code>const
int</code>.
</p>
<p>The type <code>int[]</code> and <code>int[5]</code> are compatible.  On the other
hand, <code>int</code> and <code>char *</code> are not compatible, even if the size
of their types, on the particular architecture are the same.  Also, the
amount of pointer indirection is taken into account when determining
similarity.  Consequently, <code>short *</code> is not similar to
<code>short **</code>.  Furthermore, two types that are typedefed are
considered compatible if their underlying types are compatible.
</p>
<p>An <code>enum</code> type is not considered to be compatible with another
<code>enum</code> type even if both are compatible with the same integer
type; this is what the C standard specifies.
For example, <code>enum {foo, bar}</code> is not similar to
<code>enum {hot, dog}</code>.
</p>
<p>You typically use this function in code whose execution varies
depending on the arguments&rsquo; types.  For example:
</p>
<div class="smallexample">
<pre class="smallexample">#define foo(x)                                                  \
  ({                                                           \
    typeof (x) tmp = (x);                                       \
    if (__builtin_types_compatible_p (typeof (x), long double)) \
      tmp = foo_long_double (tmp);                              \
    else if (__builtin_types_compatible_p (typeof (x), double)) \
      tmp = foo_double (tmp);                                   \
    else if (__builtin_types_compatible_p (typeof (x), float))  \
      tmp = foo_float (tmp);                                    \
    else                                                        \
      abort ();                                                 \
    tmp;                                                        \
  })
</pre></div>

<p><em>Note:</em> This construct is only available for C.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fcall_005fwith_005fstatic_005fchain-1"></a>Built-in Function: <em><var>type</var></em> <strong>__builtin_call_with_static_chain</strong> <em>(<var>call_exp</var>, <var>pointer_exp</var>)</em></dt>
<dd>
<p>The <var>call_exp</var> expression must be a function call, and the
<var>pointer_exp</var> expression must be a pointer.  The <var>pointer_exp</var>
is passed to the function call in the target&rsquo;s static chain location.
The result of builtin is the result of the function call.
</p>
<p><em>Note:</em> This builtin is only available for C.
This builtin can be used to call Go closures from C.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fchoose_005fexpr"></a>Built-in Function: <em><var>type</var></em> <strong>__builtin_choose_expr</strong> <em>(<var>const_exp</var>, <var>exp1</var>, <var>exp2</var>)</em></dt>
<dd>
<p>You can use the built-in function <code>__builtin_choose_expr</code> to
evaluate code depending on the value of a constant expression.  This
built-in function returns <var>exp1</var> if <var>const_exp</var>, which is an
integer constant expression, is nonzero.  Otherwise it returns <var>exp2</var>.
</p>
<p>This built-in function is analogous to the &lsquo;<samp>? :</samp>&rsquo; operator in C,
except that the expression returned has its type unaltered by promotion
rules.  Also, the built-in function does not evaluate the expression
that is not chosen.  For example, if <var>const_exp</var> evaluates to <code>true</code>,
<var>exp2</var> is not evaluated even if it has side effects.
</p>
<p>This built-in function can return an lvalue if the chosen argument is an
lvalue.
</p>
<p>If <var>exp1</var> is returned, the return type is the same as <var>exp1</var>&rsquo;s
type.  Similarly, if <var>exp2</var> is returned, its return type is the same
as <var>exp2</var>.
</p>
<p>Example:
</p>
<div class="smallexample">
<pre class="smallexample">#define foo(x)                                                    \
  __builtin_choose_expr (                                         \
    __builtin_types_compatible_p (typeof (x), double),            \
    foo_double (x),                                               \
    __builtin_choose_expr (                                       \
      __builtin_types_compatible_p (typeof (x), float),           \
      foo_float (x),                                              \
      /* <span class="roman">The void expression results in a compile-time error</span>  \
         <span class="roman">when assigning the result to something.</span>  */          \
      (void)0))
</pre></div>

<p><em>Note:</em> This construct is only available for C.  Furthermore, the
unused expression (<var>exp1</var> or <var>exp2</var> depending on the value of
<var>const_exp</var>) may still generate syntax errors.  This may change in
future revisions.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005ftgmath"></a>Built-in Function: <em><var>type</var></em> <strong>__builtin_tgmath</strong> <em>(<var>functions</var>, <var>arguments</var>)</em></dt>
<dd>
<p>The built-in function <code>__builtin_tgmath</code>, available only for C
and Objective-C, calls a function determined according to the rules of
<code>&lt;tgmath.h&gt;</code> macros.  It is intended to be used in
implementations of that header, so that expansions of macros from that
header only expand each of their arguments once, to avoid problems
when calls to such macros are nested inside the arguments of other
calls to such macros; in addition, it results in better diagnostics
for invalid calls to <code>&lt;tgmath.h&gt;</code> macros than implementations
using other GNU C language features.  For example, the <code>pow</code>
type-generic macro might be defined as:
</p>
<div class="smallexample">
<pre class="smallexample">#define pow(a, b) __builtin_tgmath (powf, pow, powl, \
                                    cpowf, cpow, cpowl, a, b)
</pre></div>

<p>The arguments to <code>__builtin_tgmath</code> are at least two pointers to
functions, followed by the arguments to the type-generic macro (which
will be passed as arguments to the selected function).  All the
pointers to functions must be pointers to prototyped functions, none
of which may have variable arguments, and all of which must have the
same number of parameters; the number of parameters of the first
function determines how many arguments to <code>__builtin_tgmath</code> are
interpreted as function pointers, and how many as the arguments to the
called function.
</p>
<p>The types of the specified functions must all be different, but
related to each other in the same way as a set of functions that may
be selected between by a macro in <code>&lt;tgmath.h&gt;</code>.  This means that
the functions are parameterized by a floating-point type <var>t</var>,
different for each such function.  The function return types may all
be the same type, or they may be <var>t</var> for each function, or they
may be the real type corresponding to <var>t</var> for each function (if
some of the types <var>t</var> are complex).  Likewise, for each parameter
position, the type of the parameter in that position may always be the
same type, or may be <var>t</var> for each function (this case must apply
for at least one parameter position), or may be the real type
corresponding to <var>t</var> for each function.
</p>
<p>The standard rules for <code>&lt;tgmath.h&gt;</code> macros are used to find a
common type <var>u</var> from the types of the arguments for parameters
whose types vary between the functions; complex integer types (a GNU
extension) are treated like <code>_Complex double</code> for this purpose
(or <code>_Complex _Float64</code> if all the function return types are the
same <code>_Float<var>n</var></code> or <code>_Float<var>n</var>x</code> type).
If the function return types vary, or are all the same integer type,
the function called is the one for which <var>t</var> is <var>u</var>, and it is
an error if there is no such function.  If the function return types
are all the same floating-point type, the type-generic macro is taken
to be one of those from TS 18661 that rounds the result to a narrower
type; if there is a function for which <var>t</var> is <var>u</var>, it is
called, and otherwise the first function, if any, for which <var>t</var>
has at least the range and precision of <var>u</var> is called, and it is
an error if there is no such function.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fcomplex"></a>Built-in Function: <em><var>type</var></em> <strong>__builtin_complex</strong> <em>(<var>real</var>, <var>imag</var>)</em></dt>
<dd>
<p>The built-in function <code>__builtin_complex</code> is provided for use in
implementing the ISO C11 macros <code>CMPLXF</code>, <code>CMPLX</code> and
<code>CMPLXL</code>.  <var>real</var> and <var>imag</var> must have the same type, a
real binary floating-point type, and the result has the corresponding
complex type with real and imaginary parts <var>real</var> and <var>imag</var>.
Unlike &lsquo;<samp><var>real</var> + I * <var>imag</var></samp>&rsquo;, this works even when
infinities, NaNs and negative zeros are involved.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fconstant_005fp"></a>Built-in Function: <em>int</em> <strong>__builtin_constant_p</strong> <em>(<var>exp</var>)</em></dt>
<dd><p>You can use the built-in function <code>__builtin_constant_p</code> to
determine if a value is known to be constant at compile time and hence
that GCC can perform constant-folding on expressions involving that
value.  The argument of the function is the value to test.  The function
returns the integer 1 if the argument is known to be a compile-time
constant and 0 if it is not known to be a compile-time constant.  A
return of 0 does not indicate that the value is <em>not</em> a constant,
but merely that GCC cannot prove it is a constant with the specified
value of the <samp>-O</samp> option.
</p>
<p>You typically use this function in an embedded application where
memory is a critical resource.  If you have some complex calculation,
you may want it to be folded if it involves constants, but need to call
a function if it does not.  For example:
</p>
<div class="smallexample">
<pre class="smallexample">#define Scale_Value(X)      \
  (__builtin_constant_p (X) \
  ? ((X) * SCALE + OFFSET) : Scale (X))
</pre></div>

<p>You may use this built-in function in either a macro or an inline
function.  However, if you use it in an inlined function and pass an
argument of the function as the argument to the built-in, GCC 
never returns 1 when you call the inline function with a string constant
or compound literal (see <a href="Compound-Literals.html#Compound-Literals">Compound Literals</a>) and does not return 1
when you pass a constant numeric value to the inline function unless you
specify the <samp>-O</samp> option.
</p>
<p>You may also use <code>__builtin_constant_p</code> in initializers for static
data.  For instance, you can write
</p>
<div class="smallexample">
<pre class="smallexample">static const int table[] = {
   __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1,
   /* <span class="roman">&hellip;</span> */
};
</pre></div>

<p>This is an acceptable initializer even if <var>EXPRESSION</var> is not a
constant expression, including the case where
<code>__builtin_constant_p</code> returns 1 because <var>EXPRESSION</var> can be
folded to a constant but <var>EXPRESSION</var> contains operands that are
not otherwise permitted in a static initializer (for example,
<code>0 &amp;&amp; foo ()</code>).  GCC must be more conservative about evaluating the
built-in in this case, because it has no opportunity to perform
optimization.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fis_005fconstant_005fevaluated"></a>Built-in Function: <em>bool</em> <strong>__builtin_is_constant_evaluated</strong> <em>(void)</em></dt>
<dd><p>The <code>__builtin_is_constant_evaluated</code> function is available only
in C++.  The built-in is intended to be used by implementations of
the <code>std::is_constant_evaluated</code> C++ function.  Programs should make
use of the latter function rather than invoking the built-in directly.
</p>
<p>The main use case of the built-in is to determine whether a <code>constexpr</code>
function is being called in a <code>constexpr</code> context.  A call to
the function evaluates to a core constant expression with the value
<code>true</code> if and only if it occurs within the evaluation of an expression
or conversion that is manifestly constant-evaluated as defined in the C++
standard.  Manifestly constant-evaluated contexts include constant-expressions,
the conditions of <code>constexpr if</code> statements, constraint-expressions, and
initializers of variables usable in constant expressions.   For more details
refer to the latest revision of the C++ standard.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fexpect"></a>Built-in Function: <em>long</em> <strong>__builtin_expect</strong> <em>(long <var>exp</var>, long <var>c</var>)</em></dt>
<dd><a name="index-fprofile_002darcs-1"></a>
<p>You may use <code>__builtin_expect</code> to provide the compiler with
branch prediction information.  In general, you should prefer to
use actual profile feedback for this (<samp>-fprofile-arcs</samp>), as
programmers are notoriously bad at predicting how their programs
actually perform.  However, there are applications in which this
data is hard to collect.
</p>
<p>The return value is the value of <var>exp</var>, which should be an integral
expression.  The semantics of the built-in are that it is expected that
<var>exp</var> == <var>c</var>.  For example:
</p>
<div class="smallexample">
<pre class="smallexample">if (__builtin_expect (x, 0))
  foo ();
</pre></div>

<p>indicates that we do not expect to call <code>foo</code>, since
we expect <code>x</code> to be zero.  Since you are limited to integral
expressions for <var>exp</var>, you should use constructions such as
</p>
<div class="smallexample">
<pre class="smallexample">if (__builtin_expect (ptr != NULL, 1))
  foo (*ptr);
</pre></div>

<p>when testing pointer or floating-point values.
</p>
<p>For the purposes of branch prediction optimizations, the probability that
a <code>__builtin_expect</code> expression is <code>true</code> is controlled by GCC&rsquo;s
<code>builtin-expect-probability</code> parameter, which defaults to 90%.  
</p>
<p>You can also use <code>__builtin_expect_with_probability</code> to explicitly 
assign a probability value to individual expressions.  If the built-in
is used in a loop construct, the provided probability will influence
the expected number of iterations made by loop optimizations.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fexpect_005fwith_005fprobability"></a>Built-in Function: <em>long</em> <strong>__builtin_expect_with_probability</strong></dt>
<dd><p>(long <var>exp</var>, long <var>c</var>, double <var>probability</var>)
</p>
<p>This function has the same semantics as <code>__builtin_expect</code>,
but the caller provides the expected probability that <var>exp</var> == <var>c</var>.
The last argument, <var>probability</var>, is a floating-point value in the
range 0.0 to 1.0, inclusive.  The <var>probability</var> argument must be
constant floating-point expression.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005ftrap"></a>Built-in Function: <em>void</em> <strong>__builtin_trap</strong> <em>(void)</em></dt>
<dd><p>This function causes the program to exit abnormally.  GCC implements
this function by using a target-dependent mechanism (such as
intentionally executing an illegal instruction) or by calling
<code>abort</code>.  The mechanism used may vary from release to release so
you should not rely on any particular implementation.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005funreachable"></a>Built-in Function: <em>void</em> <strong>__builtin_unreachable</strong> <em>(void)</em></dt>
<dd><p>If control flow reaches the point of the <code>__builtin_unreachable</code>,
the program is undefined.  It is useful in situations where the
compiler cannot deduce the unreachability of the code.
</p>
<p>One such case is immediately following an <code>asm</code> statement that
either never terminates, or one that transfers control elsewhere
and never returns.  In this example, without the
<code>__builtin_unreachable</code>, GCC issues a warning that control
reaches the end of a non-void function.  It also generates code
to return after the <code>asm</code>.
</p>
<div class="smallexample">
<pre class="smallexample">int f (int c, int v)
{
  if (c)
    {
      return v;
    }
  else
    {
      asm(&quot;jmp error_handler&quot;);
      __builtin_unreachable ();
    }
}
</pre></div>

<p>Because the <code>asm</code> statement unconditionally transfers control out
of the function, control never reaches the end of the function
body.  The <code>__builtin_unreachable</code> is in fact unreachable and
communicates this fact to the compiler.
</p>
<p>Another use for <code>__builtin_unreachable</code> is following a call a
function that never returns but that is not declared
<code>__attribute__((noreturn))</code>, as in this example:
</p>
<div class="smallexample">
<pre class="smallexample">void function_that_never_returns (void);

int g (int c)
{
  if (c)
    {
      return 1;
    }
  else
    {
      function_that_never_returns ();
      __builtin_unreachable ();
    }
}
</pre></div>

</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fassume_005faligned"></a>Built-in Function: <em>void *</em> <strong>__builtin_assume_aligned</strong> <em>(const void *<var>exp</var>, size_t <var>align</var>, ...)</em></dt>
<dd><p>This function returns its first argument, and allows the compiler
to assume that the returned pointer is at least <var>align</var> bytes
aligned.  This built-in can have either two or three arguments,
if it has three, the third argument should have integer type, and
if it is nonzero means misalignment offset.  For example:
</p>
<div class="smallexample">
<pre class="smallexample">void *x = __builtin_assume_aligned (arg, 16);
</pre></div>

<p>means that the compiler can assume <code>x</code>, set to <code>arg</code>, is at least
16-byte aligned, while:
</p>
<div class="smallexample">
<pre class="smallexample">void *x = __builtin_assume_aligned (arg, 32, 8);
</pre></div>

<p>means that the compiler can assume for <code>x</code>, set to <code>arg</code>, that
<code>(char *) x - 8</code> is 32-byte aligned.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fLINE"></a>Built-in Function: <em>int</em> <strong>__builtin_LINE</strong> <em>()</em></dt>
<dd><p>This function is the equivalent of the preprocessor <code>__LINE__</code>
macro and returns a constant integer expression that evaluates to
the line number of the invocation of the built-in.  When used as a C++
default argument for a function <var>F</var>, it returns the line number
of the call to <var>F</var>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fFUNCTION"></a>Built-in Function: <em>const char *</em> <strong>__builtin_FUNCTION</strong> <em>()</em></dt>
<dd><p>This function is the equivalent of the <code>__FUNCTION__</code> symbol
and returns an address constant pointing to the name of the function
from which the built-in was invoked, or the empty string if
the invocation is not at function scope.  When used as a C++ default
argument for a function <var>F</var>, it returns the name of <var>F</var>&rsquo;s
caller or the empty string if the call was not made at function
scope.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fFILE"></a>Built-in Function: <em>const char *</em> <strong>__builtin_FILE</strong> <em>()</em></dt>
<dd><p>This function is the equivalent of the preprocessor <code>__FILE__</code>
macro and returns an address constant pointing to the file name
containing the invocation of the built-in, or the empty string if
the invocation is not at function scope.  When used as a C++ default
argument for a function <var>F</var>, it returns the file name of the call
to <var>F</var> or the empty string if the call was not made at function
scope.
</p>
<p>For example, in the following, each call to function <code>foo</code> will
print a line similar to <code>&quot;file.c:123: foo: message&quot;</code> with the name
of the file and the line number of the <code>printf</code> call, the name of
the function <code>foo</code>, followed by the word <code>message</code>.
</p>
<div class="smallexample">
<pre class="smallexample">const char*
function (const char *func = __builtin_FUNCTION ())
{
  return func;
}

void foo (void)
{
  printf (&quot;%s:%i: %s: message\n&quot;, file (), line (), function ());
}
</pre></div>

</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005f_005f_005fclear_005fcache"></a>Built-in Function: <em>void</em> <strong>__builtin___clear_cache</strong> <em>(void *<var>begin</var>, void *<var>end</var>)</em></dt>
<dd><p>This function is used to flush the processor&rsquo;s instruction cache for
the region of memory between <var>begin</var> inclusive and <var>end</var>
exclusive.  Some targets require that the instruction cache be
flushed, after modifying memory containing code, in order to obtain
deterministic behavior.
</p>
<p>If the target does not require instruction cache flushes,
<code>__builtin___clear_cache</code> has no effect.  Otherwise either
instructions are emitted in-line to clear the instruction cache or a
call to the <code>__clear_cache</code> function in libgcc is made.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fprefetch"></a>Built-in Function: <em>void</em> <strong>__builtin_prefetch</strong> <em>(const void *<var>addr</var>, ...)</em></dt>
<dd><p>This function is used to minimize cache-miss latency by moving data into
a cache before it is accessed.
You can insert calls to <code>__builtin_prefetch</code> into code for which
you know addresses of data in memory that is likely to be accessed soon.
If the target supports them, data prefetch instructions are generated.
If the prefetch is done early enough before the access then the data will
be in the cache by the time it is accessed.
</p>
<p>The value of <var>addr</var> is the address of the memory to prefetch.
There are two optional arguments, <var>rw</var> and <var>locality</var>.
The value of <var>rw</var> is a compile-time constant one or zero; one
means that the prefetch is preparing for a write to the memory address
and zero, the default, means that the prefetch is preparing for a read.
The value <var>locality</var> must be a compile-time constant integer between
zero and three.  A value of zero means that the data has no temporal
locality, so it need not be left in the cache after the access.  A value
of three means that the data has a high degree of temporal locality and
should be left in all levels of cache possible.  Values of one and two
mean, respectively, a low or moderate degree of temporal locality.  The
default is three.
</p>
<div class="smallexample">
<pre class="smallexample">for (i = 0; i &lt; n; i++)
  {
    a[i] = a[i] + b[i];
    __builtin_prefetch (&amp;a[i+j], 1, 1);
    __builtin_prefetch (&amp;b[i+j], 0, 1);
    /* <span class="roman">&hellip;</span> */
  }
</pre></div>

<p>Data prefetch does not generate faults if <var>addr</var> is invalid, but
the address expression itself must be valid.  For example, a prefetch
of <code>p-&gt;next</code> does not fault if <code>p-&gt;next</code> is not a valid
address, but evaluation faults if <code>p</code> is not a valid address.
</p>
<p>If the target does not support data prefetch, the address expression
is evaluated if it includes side effects but no other code is generated
and GCC does not issue a warning.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fobject_005fsize-3"></a>Built-in Function: <em>size_t</em> <strong>__builtin_object_size</strong> <em>(const void * <var>ptr</var>, int <var>type</var>)</em></dt>
<dd><p>Returns the size of an object pointed to by <var>ptr</var>.  See <a href="Object-Size-Checking.html#Object-Size-Checking">Object Size Checking</a>, for a detailed description of the function.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fhuge_005fval"></a>Built-in Function: <em>double</em> <strong>__builtin_huge_val</strong> <em>(void)</em></dt>
<dd><p>Returns a positive infinity, if supported by the floating-point format,
else <code>DBL_MAX</code>.  This function is suitable for implementing the
ISO C macro <code>HUGE_VAL</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fhuge_005fvalf"></a>Built-in Function: <em>float</em> <strong>__builtin_huge_valf</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_huge_val</code>, except the return type is <code>float</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fhuge_005fvall"></a>Built-in Function: <em>long double</em> <strong>__builtin_huge_vall</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_huge_val</code>, except the return
type is <code>long double</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fhuge_005fvalfn"></a>Built-in Function: <em>_Float<var>n</var></em> <strong>__builtin_huge_valf<var>n</var></strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_huge_val</code>, except the return type is
<code>_Float<var>n</var></code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fhuge_005fvalfnx"></a>Built-in Function: <em>_Float<var>n</var>x</em> <strong>__builtin_huge_valf<var>n</var>x</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_huge_val</code>, except the return type is
<code>_Float<var>n</var>x</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005ffpclassify-1"></a>Built-in Function: <em>int</em> <strong>__builtin_fpclassify</strong> <em>(int, int, int, int, int, ...)</em></dt>
<dd><p>This built-in implements the C99 fpclassify functionality.  The first
five int arguments should be the target library&rsquo;s notion of the
possible FP classes and are used for return values.  They must be
constant values and they must appear in this order: <code>FP_NAN</code>,
<code>FP_INFINITE</code>, <code>FP_NORMAL</code>, <code>FP_SUBNORMAL</code> and
<code>FP_ZERO</code>.  The ellipsis is for exactly one floating-point value
to classify.  GCC treats the last argument as type-generic, which
means it does not do default promotion from float to double.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005finf"></a>Built-in Function: <em>double</em> <strong>__builtin_inf</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_huge_val</code>, except a warning is generated
if the target floating-point format does not support infinities.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005finfd32"></a>Built-in Function: <em>_Decimal32</em> <strong>__builtin_infd32</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_inf</code>, except the return type is <code>_Decimal32</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005finfd64"></a>Built-in Function: <em>_Decimal64</em> <strong>__builtin_infd64</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_inf</code>, except the return type is <code>_Decimal64</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005finfd128"></a>Built-in Function: <em>_Decimal128</em> <strong>__builtin_infd128</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_inf</code>, except the return type is <code>_Decimal128</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005finff"></a>Built-in Function: <em>float</em> <strong>__builtin_inff</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_inf</code>, except the return type is <code>float</code>.
This function is suitable for implementing the ISO C99 macro <code>INFINITY</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005finfl"></a>Built-in Function: <em>long double</em> <strong>__builtin_infl</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_inf</code>, except the return
type is <code>long double</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005finffn"></a>Built-in Function: <em>_Float<var>n</var></em> <strong>__builtin_inff<var>n</var></strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_inf</code>, except the return
type is <code>_Float<var>n</var></code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005finffnx"></a>Built-in Function: <em>_Float<var>n</var></em> <strong>__builtin_inff<var>n</var>x</strong> <em>(void)</em></dt>
<dd><p>Similar to <code>__builtin_inf</code>, except the return
type is <code>_Float<var>n</var>x</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fisinf_005fsign-1"></a>Built-in Function: <em>int</em> <strong>__builtin_isinf_sign</strong> <em>(...)</em></dt>
<dd><p>Similar to <code>isinf</code>, except the return value is -1 for
an argument of <code>-Inf</code> and 1 for an argument of <code>+Inf</code>.
Note while the parameter list is an
ellipsis, this function only accepts exactly one floating-point
argument.  GCC treats this parameter as type-generic, which means it
does not do default promotion from float to double.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnan"></a>Built-in Function: <em>double</em> <strong>__builtin_nan</strong> <em>(const char *str)</em></dt>
<dd><p>This is an implementation of the ISO C99 function <code>nan</code>.
</p>
<p>Since ISO C99 defines this function in terms of <code>strtod</code>, which we
do not implement, a description of the parsing is in order.  The string
is parsed as by <code>strtol</code>; that is, the base is recognized by
leading &lsquo;<samp>0</samp>&rsquo; or &lsquo;<samp>0x</samp>&rsquo; prefixes.  The number parsed is placed
in the significand such that the least significant bit of the number
is at the least significant bit of the significand.  The number is
truncated to fit the significand field provided.  The significand is
forced to be a quiet NaN.
</p>
<p>This function, if given a string literal all of which would have been
consumed by <code>strtol</code>, is evaluated early enough that it is considered a
compile-time constant.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnand32"></a>Built-in Function: <em>_Decimal32</em> <strong>__builtin_nand32</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the return type is <code>_Decimal32</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnand64"></a>Built-in Function: <em>_Decimal64</em> <strong>__builtin_nand64</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the return type is <code>_Decimal64</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnand128"></a>Built-in Function: <em>_Decimal128</em> <strong>__builtin_nand128</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the return type is <code>_Decimal128</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnanf"></a>Built-in Function: <em>float</em> <strong>__builtin_nanf</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the return type is <code>float</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnanl"></a>Built-in Function: <em>long double</em> <strong>__builtin_nanl</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the return type is <code>long double</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnanfn"></a>Built-in Function: <em>_Float<var>n</var></em> <strong>__builtin_nanf<var>n</var></strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the return type is
<code>_Float<var>n</var></code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnanfnx"></a>Built-in Function: <em>_Float<var>n</var>x</em> <strong>__builtin_nanf<var>n</var>x</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the return type is
<code>_Float<var>n</var>x</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnans"></a>Built-in Function: <em>double</em> <strong>__builtin_nans</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nan</code>, except the significand is forced
to be a signaling NaN.  The <code>nans</code> function is proposed by
<a href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n965.htm">WG14 N965</a>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnansf"></a>Built-in Function: <em>float</em> <strong>__builtin_nansf</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nans</code>, except the return type is <code>float</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnansl"></a>Built-in Function: <em>long double</em> <strong>__builtin_nansl</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nans</code>, except the return type is <code>long double</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnansfn"></a>Built-in Function: <em>_Float<var>n</var></em> <strong>__builtin_nansf<var>n</var></strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nans</code>, except the return type is
<code>_Float<var>n</var></code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fnansfnx"></a>Built-in Function: <em>_Float<var>n</var>x</em> <strong>__builtin_nansf<var>n</var>x</strong> <em>(const char *str)</em></dt>
<dd><p>Similar to <code>__builtin_nans</code>, except the return type is
<code>_Float<var>n</var>x</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fffs"></a>Built-in Function: <em>int</em> <strong>__builtin_ffs</strong> <em>(int x)</em></dt>
<dd><p>Returns one plus the index of the least significant 1-bit of <var>x</var>, or
if <var>x</var> is zero, returns zero.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fclz"></a>Built-in Function: <em>int</em> <strong>__builtin_clz</strong> <em>(unsigned int x)</em></dt>
<dd><p>Returns the number of leading 0-bits in <var>x</var>, starting at the most
significant bit position.  If <var>x</var> is 0, the result is undefined.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fctz"></a>Built-in Function: <em>int</em> <strong>__builtin_ctz</strong> <em>(unsigned int x)</em></dt>
<dd><p>Returns the number of trailing 0-bits in <var>x</var>, starting at the least
significant bit position.  If <var>x</var> is 0, the result is undefined.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fclrsb"></a>Built-in Function: <em>int</em> <strong>__builtin_clrsb</strong> <em>(int x)</em></dt>
<dd><p>Returns the number of leading redundant sign bits in <var>x</var>, i.e. the
number of bits following the most significant bit that are identical
to it.  There are no special cases for 0 or other values. 
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fpopcount"></a>Built-in Function: <em>int</em> <strong>__builtin_popcount</strong> <em>(unsigned int x)</em></dt>
<dd><p>Returns the number of 1-bits in <var>x</var>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fparity"></a>Built-in Function: <em>int</em> <strong>__builtin_parity</strong> <em>(unsigned int x)</em></dt>
<dd><p>Returns the parity of <var>x</var>, i.e. the number of 1-bits in <var>x</var>
modulo 2.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fffsl"></a>Built-in Function: <em>int</em> <strong>__builtin_ffsl</strong> <em>(long)</em></dt>
<dd><p>Similar to <code>__builtin_ffs</code>, except the argument type is
<code>long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fclzl"></a>Built-in Function: <em>int</em> <strong>__builtin_clzl</strong> <em>(unsigned long)</em></dt>
<dd><p>Similar to <code>__builtin_clz</code>, except the argument type is
<code>unsigned long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fctzl"></a>Built-in Function: <em>int</em> <strong>__builtin_ctzl</strong> <em>(unsigned long)</em></dt>
<dd><p>Similar to <code>__builtin_ctz</code>, except the argument type is
<code>unsigned long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fclrsbl"></a>Built-in Function: <em>int</em> <strong>__builtin_clrsbl</strong> <em>(long)</em></dt>
<dd><p>Similar to <code>__builtin_clrsb</code>, except the argument type is
<code>long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fpopcountl"></a>Built-in Function: <em>int</em> <strong>__builtin_popcountl</strong> <em>(unsigned long)</em></dt>
<dd><p>Similar to <code>__builtin_popcount</code>, except the argument type is
<code>unsigned long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fparityl"></a>Built-in Function: <em>int</em> <strong>__builtin_parityl</strong> <em>(unsigned long)</em></dt>
<dd><p>Similar to <code>__builtin_parity</code>, except the argument type is
<code>unsigned long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fffsll"></a>Built-in Function: <em>int</em> <strong>__builtin_ffsll</strong> <em>(long long)</em></dt>
<dd><p>Similar to <code>__builtin_ffs</code>, except the argument type is
<code>long long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fclzll"></a>Built-in Function: <em>int</em> <strong>__builtin_clzll</strong> <em>(unsigned long long)</em></dt>
<dd><p>Similar to <code>__builtin_clz</code>, except the argument type is
<code>unsigned long long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fctzll"></a>Built-in Function: <em>int</em> <strong>__builtin_ctzll</strong> <em>(unsigned long long)</em></dt>
<dd><p>Similar to <code>__builtin_ctz</code>, except the argument type is
<code>unsigned long long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fclrsbll"></a>Built-in Function: <em>int</em> <strong>__builtin_clrsbll</strong> <em>(long long)</em></dt>
<dd><p>Similar to <code>__builtin_clrsb</code>, except the argument type is
<code>long long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fpopcountll"></a>Built-in Function: <em>int</em> <strong>__builtin_popcountll</strong> <em>(unsigned long long)</em></dt>
<dd><p>Similar to <code>__builtin_popcount</code>, except the argument type is
<code>unsigned long long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fparityll"></a>Built-in Function: <em>int</em> <strong>__builtin_parityll</strong> <em>(unsigned long long)</em></dt>
<dd><p>Similar to <code>__builtin_parity</code>, except the argument type is
<code>unsigned long long</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fpowi-1"></a>Built-in Function: <em>double</em> <strong>__builtin_powi</strong> <em>(double, int)</em></dt>
<dd><p>Returns the first argument raised to the power of the second.  Unlike the
<code>pow</code> function no guarantees about precision and rounding are made.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fpowif-1"></a>Built-in Function: <em>float</em> <strong>__builtin_powif</strong> <em>(float, int)</em></dt>
<dd><p>Similar to <code>__builtin_powi</code>, except the argument and return types
are <code>float</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fpowil-1"></a>Built-in Function: <em>long double</em> <strong>__builtin_powil</strong> <em>(long double, int)</em></dt>
<dd><p>Similar to <code>__builtin_powi</code>, except the argument and return types
are <code>long double</code>.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fbswap16"></a>Built-in Function: <em>uint16_t</em> <strong>__builtin_bswap16</strong> <em>(uint16_t x)</em></dt>
<dd><p>Returns <var>x</var> with the order of the bytes reversed; for example,
<code>0xaabb</code> becomes <code>0xbbaa</code>.  Byte here always means
exactly 8 bits.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fbswap32"></a>Built-in Function: <em>uint32_t</em> <strong>__builtin_bswap32</strong> <em>(uint32_t x)</em></dt>
<dd><p>Similar to <code>__builtin_bswap16</code>, except the argument and return types
are 32 bit.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fbswap64"></a>Built-in Function: <em>uint64_t</em> <strong>__builtin_bswap64</strong> <em>(uint64_t x)</em></dt>
<dd><p>Similar to <code>__builtin_bswap32</code>, except the argument and return types
are 64 bit.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fextend_005fpointer-1"></a>Built-in Function: <em>Pmode</em> <strong>__builtin_extend_pointer</strong> <em>(void * x)</em></dt>
<dd><p>On targets where the user visible pointer size is smaller than the size
of an actual hardware address this function returns the extended user
pointer.  Targets where this is true included ILP32 mode on x86_64 or
Aarch64.  This function is mainly useful when writing inline assembly
code.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fgoacc_005fparlevel_005fid"></a>Built-in Function: <em>int</em> <strong>__builtin_goacc_parlevel_id</strong> <em>(int x)</em></dt>
<dd><p>Returns the openacc gang, worker or vector id depending on whether <var>x</var> is
0, 1 or 2.
</p></dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fgoacc_005fparlevel_005fsize"></a>Built-in Function: <em>int</em> <strong>__builtin_goacc_parlevel_size</strong> <em>(int x)</em></dt>
<dd><p>Returns the openacc gang, worker or vector size depending on whether <var>x</var> is
0, 1 or 2.
</p></dd></dl>

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