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<a name="Cross-Compilation-and-Floating-Point"></a>
<h3 class="section">18.22 Cross Compilation and Floating Point</h3>
<a name="index-cross-compilation-and-floating-point"></a>
<a name="index-floating-point-and-cross-compilation"></a>

<p>While all modern machines use twos-complement representation for integers,
there are a variety of representations for floating point numbers.  This
means that in a cross-compiler the representation of floating point numbers
in the compiled program may be different from that used in the machine
doing the compilation.
</p>
<p>Because different representation systems may offer different amounts of
range and precision, all floating point constants must be represented in
the target machine&rsquo;s format.  Therefore, the cross compiler cannot
safely use the host machine&rsquo;s floating point arithmetic; it must emulate
the target&rsquo;s arithmetic.  To ensure consistency, GCC always uses
emulation to work with floating point values, even when the host and
target floating point formats are identical.
</p>
<p>The following macros are provided by <samp>real.h</samp> for the compiler to
use.  All parts of the compiler which generate or optimize
floating-point calculations must use these macros.  They may evaluate
their operands more than once, so operands must not have side effects.
</p>
<dl>
<dt><a name="index-REAL_005fVALUE_005fTYPE"></a>Macro: <strong>REAL_VALUE_TYPE</strong></dt>
<dd><p>The C data type to be used to hold a floating point value in the target
machine&rsquo;s format.  Typically this is a <code>struct</code> containing an
array of <code>HOST_WIDE_INT</code>, but all code should treat it as an opaque
quantity.
</p></dd></dl>

<dl>
<dt><a name="index-REAL_005fVALUE_005fFIX"></a>Macro: <em>HOST_WIDE_INT</em> <strong>REAL_VALUE_FIX</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt>
<dd><p>Truncates <var>x</var> to a signed integer, rounding toward zero.
</p></dd></dl>

<dl>
<dt><a name="index-REAL_005fVALUE_005fUNSIGNED_005fFIX"></a>Macro: <em>unsigned HOST_WIDE_INT</em> <strong>REAL_VALUE_UNSIGNED_FIX</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt>
<dd><p>Truncates <var>x</var> to an unsigned integer, rounding toward zero.  If
<var>x</var> is negative, returns zero.
</p></dd></dl>

<dl>
<dt><a name="index-REAL_005fVALUE_005fATOF"></a>Macro: <em>REAL_VALUE_TYPE</em> <strong>REAL_VALUE_ATOF</strong> <em>(const char *<var>string</var>, machine_mode <var>mode</var>)</em></dt>
<dd><p>Converts <var>string</var> into a floating point number in the target machine&rsquo;s
representation for mode <var>mode</var>.  This routine can handle both
decimal and hexadecimal floating point constants, using the syntax
defined by the C language for both.
</p></dd></dl>

<dl>
<dt><a name="index-REAL_005fVALUE_005fNEGATIVE"></a>Macro: <em>int</em> <strong>REAL_VALUE_NEGATIVE</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt>
<dd><p>Returns 1 if <var>x</var> is negative (including negative zero), 0 otherwise.
</p></dd></dl>

<dl>
<dt><a name="index-REAL_005fVALUE_005fISINF"></a>Macro: <em>int</em> <strong>REAL_VALUE_ISINF</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt>
<dd><p>Determines whether <var>x</var> represents infinity (positive or negative).
</p></dd></dl>

<dl>
<dt><a name="index-REAL_005fVALUE_005fISNAN"></a>Macro: <em>int</em> <strong>REAL_VALUE_ISNAN</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt>
<dd><p>Determines whether <var>x</var> represents a &ldquo;NaN&rdquo; (not-a-number).
</p></dd></dl>

<dl>
<dt><a name="index-REAL_005fVALUE_005fNEGATE"></a>Macro: <em>REAL_VALUE_TYPE</em> <strong>REAL_VALUE_NEGATE</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt>
<dd><p>Returns the negative of the floating point value <var>x</var>.
</p></dd></dl>

<dl>
<dt><a name="index-REAL_005fVALUE_005fABS"></a>Macro: <em>REAL_VALUE_TYPE</em> <strong>REAL_VALUE_ABS</strong> <em>(REAL_VALUE_TYPE <var>x</var>)</em></dt>
<dd><p>Returns the absolute value of <var>x</var>.
</p></dd></dl>

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