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<h2 class="chapter">4 The GCC low-level runtime library</h2>
<p>GCC provides a low-level runtime library, <samp><span class="file">libgcc.a</span></samp> or
<samp><span class="file">libgcc_s.so.1</span></samp> on some platforms. GCC generates calls to
routines in this library automatically, whenever it needs to perform
some operation that is too complicated to emit inline code for.
<p>Most of the routines in <code>libgcc</code> handle arithmetic operations
that the target processor cannot perform directly. This includes
integer multiply and divide on some machines, and all floating-point
and fixed-point operations on other machines. <code>libgcc</code> also includes
routines for exception handling, and a handful of miscellaneous operations.
<p>Some of these routines can be defined in mostly machine-independent C.
Others must be hand-written in assembly language for each processor
that needs them.
<p>GCC will also generate calls to C library routines, such as
<code>memcpy</code> and <code>memset</code>, in some cases. The set of routines
that GCC may possibly use is documented in <a href="../gcc/Other-Builtins.html#Other-Builtins">Other Builtins</a>.
<p>These routines take arguments and return values of a specific machine
mode, not a specific C type. See <a href="Machine-Modes.html#Machine-Modes">Machine Modes</a>, for an explanation
of this concept. For illustrative purposes, in this chapter the
floating point type <code>float</code> is assumed to correspond to <code>SFmode</code>;
<code>double</code> to <code>DFmode</code>; and <code>long double<!-- /@w --></code> to both
<code>TFmode</code> and <code>XFmode</code>. Similarly, the integer types <code>int</code>
and <code>unsigned int<!-- /@w --></code> correspond to <code>SImode</code>; <code>long</code> and
<code>unsigned long<!-- /@w --></code> to <code>DImode</code>; and <code>long long<!-- /@w --></code> and
<code>unsigned long long<!-- /@w --></code> to <code>TImode</code>.
<ul class="menu">
<li><a accesskey="1" href="Integer-library-routines.html#Integer-library-routines">Integer library routines</a>
<li><a accesskey="2" href="Soft-float-library-routines.html#Soft-float-library-routines">Soft float library routines</a>
<li><a accesskey="3" href="Decimal-float-library-routines.html#Decimal-float-library-routines">Decimal float library routines</a>
<li><a accesskey="4" href="Fixed_002dpoint-fractional-library-routines.html#Fixed_002dpoint-fractional-library-routines">Fixed-point fractional library routines</a>
<li><a accesskey="5" href="Exception-handling-routines.html#Exception-handling-routines">Exception handling routines</a>
<li><a accesskey="6" href="Miscellaneous-routines.html#Miscellaneous-routines">Miscellaneous routines</a>
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