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<a name="Library-Calls"></a>
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<hr>
<a name="Implicit-Calls-to-Library-Routines"></a>
<h3 class="section">18.12 Implicit Calls to Library Routines</h3>
<a name="index-library-subroutine-names"></a>
<a name="index-libgcc_002ea"></a>

<p>Here is an explanation of implicit calls to library routines.
</p>
<dl>
<dt><a name="index-DECLARE_005fLIBRARY_005fRENAMES"></a>Macro: <strong>DECLARE_LIBRARY_RENAMES</strong></dt>
<dd><p>This macro, if defined, should expand to a piece of C code that will get
expanded when compiling functions for libgcc.a.  It can be used to
provide alternate names for GCC&rsquo;s internal library functions if there
are ABI-mandated names that the compiler should provide.
</p></dd></dl>

<a name="index-set_005foptab_005flibfunc"></a>
<a name="index-init_005fone_005flibfunc"></a>
<dl>
<dt><a name="index-TARGET_005fINIT_005fLIBFUNCS"></a>Target Hook: <em>void</em> <strong>TARGET_INIT_LIBFUNCS</strong> <em>(void)</em></dt>
<dd><p>This hook should declare additional library routines or rename
existing ones, using the functions <code>set_optab_libfunc</code> and
<code>init_one_libfunc</code> defined in <samp>optabs.c</samp>.
<code>init_optabs</code> calls this macro after initializing all the normal
library routines.
</p>
<p>The default is to do nothing.  Most ports don&rsquo;t need to define this hook.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fLIBFUNC_005fGNU_005fPREFIX"></a>Target Hook: <em>bool</em> <strong>TARGET_LIBFUNC_GNU_PREFIX</strong></dt>
<dd><p>If false (the default), internal library routines start with two
underscores.  If set to true, these routines start with <code>__gnu_</code>
instead.  E.g., <code>__muldi3</code> changes to <code>__gnu_muldi3</code>.  This
currently only affects functions defined in <samp>libgcc2.c</samp>.  If this
is set to true, the <samp>tm.h</samp> file must also
<code>#define LIBGCC2_GNU_PREFIX</code>.
</p></dd></dl>

<dl>
<dt><a name="index-FLOAT_005fLIB_005fCOMPARE_005fRETURNS_005fBOOL"></a>Macro: <strong>FLOAT_LIB_COMPARE_RETURNS_BOOL</strong> <em>(<var>mode</var>, <var>comparison</var>)</em></dt>
<dd><p>This macro should return <code>true</code> if the library routine that
implements the floating point comparison operator <var>comparison</var> in
mode <var>mode</var> will return a boolean, and <var>false</var> if it will
return a tristate.
</p>
<p>GCC&rsquo;s own floating point libraries return tristates from the
comparison operators, so the default returns false always.  Most ports
don&rsquo;t need to define this macro.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fLIB_005fINT_005fCMP_005fBIASED"></a>Macro: <strong>TARGET_LIB_INT_CMP_BIASED</strong></dt>
<dd><p>This macro should evaluate to <code>true</code> if the integer comparison
functions (like <code>__cmpdi2</code>) return 0 to indicate that the first
operand is smaller than the second, 1 to indicate that they are equal,
and 2 to indicate that the first operand is greater than the second.
If this macro evaluates to <code>false</code> the comparison functions return
-1, 0, and 1 instead of 0, 1, and 2.  If the target uses the routines
in <samp>libgcc.a</samp>, you do not need to define this macro.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fHAS_005fNO_005fHW_005fDIVIDE"></a>Macro: <strong>TARGET_HAS_NO_HW_DIVIDE</strong></dt>
<dd><p>This macro should be defined if the target has no hardware divide
instructions.  If this macro is defined, GCC will use an algorithm which
make use of simple logical and arithmetic operations for 64-bit
division.  If the macro is not defined, GCC will use an algorithm which
make use of a 64-bit by 32-bit divide primitive.
</p></dd></dl>

<a name="index-EDOM_002c-implicit-usage"></a>
<a name="index-matherr"></a>
<dl>
<dt><a name="index-TARGET_005fEDOM"></a>Macro: <strong>TARGET_EDOM</strong></dt>
<dd><p>The value of <code>EDOM</code> on the target machine, as a C integer constant
expression.  If you don&rsquo;t define this macro, GCC does not attempt to
deposit the value of <code>EDOM</code> into <code>errno</code> directly.  Look in
<samp>/usr/include/errno.h</samp> to find the value of <code>EDOM</code> on your
system.
</p>
<p>If you do not define <code>TARGET_EDOM</code>, then compiled code reports
domain errors by calling the library function and letting it report the
error.  If mathematical functions on your system use <code>matherr</code> when
there is an error, then you should leave <code>TARGET_EDOM</code> undefined so
that <code>matherr</code> is used normally.
</p></dd></dl>

<a name="index-errno_002c-implicit-usage"></a>
<dl>
<dt><a name="index-GEN_005fERRNO_005fRTX"></a>Macro: <strong>GEN_ERRNO_RTX</strong></dt>
<dd><p>Define this macro as a C expression to create an rtl expression that
refers to the global &ldquo;variable&rdquo; <code>errno</code>.  (On certain systems,
<code>errno</code> may not actually be a variable.)  If you don&rsquo;t define this
macro, a reasonable default is used.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fLIBC_005fHAS_005fFUNCTION"></a>Target Hook: <em>bool</em> <strong>TARGET_LIBC_HAS_FUNCTION</strong> <em>(enum function_class <var>fn_class</var>)</em></dt>
<dd><p>This hook determines whether a function from a class of functions
<var>fn_class</var> is present in the target C library.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fLIBC_005fHAS_005fFAST_005fFUNCTION"></a>Target Hook: <em>bool</em> <strong>TARGET_LIBC_HAS_FAST_FUNCTION</strong> <em>(int <var>fcode</var>)</em></dt>
<dd><p>This hook determines whether a function from a class of functions
<code>(enum function_class)</code><var>fcode</var> has a fast implementation.
</p></dd></dl>

<dl>
<dt><a name="index-NEXT_005fOBJC_005fRUNTIME"></a>Macro: <strong>NEXT_OBJC_RUNTIME</strong></dt>
<dd><p>Set this macro to 1 to use the &quot;NeXT&quot; Objective-C message sending conventions
by default.  This calling convention involves passing the object, the selector
and the method arguments all at once to the method-lookup library function.
This is the usual setting when targeting Darwin/Mac OS X systems, which have
the NeXT runtime installed.
</p>
<p>If the macro is set to 0, the &quot;GNU&quot; Objective-C message sending convention
will be used by default.  This convention passes just the object and the
selector to the method-lookup function, which returns a pointer to the method.
</p>
<p>In either case, it remains possible to select code-generation for the alternate
scheme, by means of compiler command line switches.
</p></dd></dl>

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