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<a name="Integer-Overflow-Builtins"></a>
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<p>
Next: <a href="x86-specific-memory-model-extensions-for-transactional-memory.html#x86-specific-memory-model-extensions-for-transactional-memory" accesskey="n" rel="next">x86 specific memory model extensions for transactional memory</a>, Previous: <a href="_005f_005fatomic-Builtins.html#g_t_005f_005fatomic-Builtins" accesskey="p" rel="prev">__atomic Builtins</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Built_002din-Functions-to-Perform-Arithmetic-with-Overflow-Checking"></a>
<h3 class="section">6.54 Built-in Functions to Perform Arithmetic with Overflow Checking</h3>

<p>The following built-in functions allow performing simple arithmetic operations
together with checking whether the operations overflowed.
</p>
<dl>
<dt><a name="index-_005f_005fbuiltin_005fadd_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_add_overflow</strong> <em>(<var>type1</var> a, <var>type2</var> b, <var>type3</var> *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fsadd_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_sadd_overflow</strong> <em>(int a, int b, int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fsaddl_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_saddl_overflow</strong> <em>(long int a, long int b, long int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fsaddll_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_saddll_overflow</strong> <em>(long long int a, long long int b, long long int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fuadd_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_uadd_overflow</strong> <em>(unsigned int a, unsigned int b, unsigned int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fuaddl_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_uaddl_overflow</strong> <em>(unsigned long int a, unsigned long int b, unsigned long int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fuaddll_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_uaddll_overflow</strong> <em>(unsigned long long int a, unsigned long long int b, unsigned long long int *res)</em></dt>
<dd>
<p>These built-in functions promote the first two operands into infinite precision signed
type and perform addition on those promoted operands.  The result is then
cast to the type the third pointer argument points to and stored there.
If the stored result is equal to the infinite precision result, the built-in
functions return false, otherwise they return true.  As the addition is
performed in infinite signed precision, these built-in functions have fully defined
behavior for all argument values.
</p>
<p>The first built-in function allows arbitrary integral types for operands and
the result type must be pointer to some integral type other than enumerated or
boolean type, the rest of the built-in functions have explicit integer types.
</p>
<p>The compiler will attempt to use hardware instructions to implement
these built-in functions where possible, like conditional jump on overflow
after addition, conditional jump on carry etc.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fsub_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_sub_overflow</strong> <em>(<var>type1</var> a, <var>type2</var> b, <var>type3</var> *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fssub_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_ssub_overflow</strong> <em>(int a, int b, int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fssubl_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_ssubl_overflow</strong> <em>(long int a, long int b, long int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fssubll_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_ssubll_overflow</strong> <em>(long long int a, long long int b, long long int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fusub_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_usub_overflow</strong> <em>(unsigned int a, unsigned int b, unsigned int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fusubl_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_usubl_overflow</strong> <em>(unsigned long int a, unsigned long int b, unsigned long int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fusubll_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_usubll_overflow</strong> <em>(unsigned long long int a, unsigned long long int b, unsigned long long int *res)</em></dt>
<dd>
<p>These built-in functions are similar to the add overflow checking built-in
functions above, except they perform subtraction, subtract the second argument
from the first one, instead of addition.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005fmul_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_mul_overflow</strong> <em>(<var>type1</var> a, <var>type2</var> b, <var>type3</var> *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fsmul_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_smul_overflow</strong> <em>(int a, int b, int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fsmull_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_smull_overflow</strong> <em>(long int a, long int b, long int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fsmulll_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_smulll_overflow</strong> <em>(long long int a, long long int b, long long int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fumul_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_umul_overflow</strong> <em>(unsigned int a, unsigned int b, unsigned int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fumull_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_umull_overflow</strong> <em>(unsigned long int a, unsigned long int b, unsigned long int *res)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fumulll_005foverflow"></a>Built-in Function: <em>bool</em> <strong>__builtin_umulll_overflow</strong> <em>(unsigned long long int a, unsigned long long int b, unsigned long long int *res)</em></dt>
<dd>
<p>These built-in functions are similar to the add overflow checking built-in
functions above, except they perform multiplication, instead of addition.
</p>
</dd></dl>

<p>The following built-in functions allow checking if simple arithmetic operation
would overflow.
</p>
<dl>
<dt><a name="index-_005f_005fbuiltin_005fadd_005foverflow_005fp"></a>Built-in Function: <em>bool</em> <strong>__builtin_add_overflow_p</strong> <em>(<var>type1</var> a, <var>type2</var> b, <var>type3</var> c)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fsub_005foverflow_005fp"></a>Built-in Function: <em>bool</em> <strong>__builtin_sub_overflow_p</strong> <em>(<var>type1</var> a, <var>type2</var> b, <var>type3</var> c)</em></dt>
<dt><a name="index-_005f_005fbuiltin_005fmul_005foverflow_005fp"></a>Built-in Function: <em>bool</em> <strong>__builtin_mul_overflow_p</strong> <em>(<var>type1</var> a, <var>type2</var> b, <var>type3</var> c)</em></dt>
<dd>
<p>These built-in functions are similar to <code>__builtin_add_overflow</code>,
<code>__builtin_sub_overflow</code>, or <code>__builtin_mul_overflow</code>, except that
they don&rsquo;t store the result of the arithmetic operation anywhere and the
last argument is not a pointer, but some expression with integral type other
than enumerated or boolean type.
</p>
<p>The built-in functions promote the first two operands into infinite precision signed type
and perform addition on those promoted operands. The result is then
cast to the type of the third argument.  If the cast result is equal to the infinite
precision result, the built-in functions return false, otherwise they return true.
The value of the third argument is ignored, just the side-effects in the third argument
are evaluated, and no integral argument promotions are performed on the last argument.
If the third argument is a bit-field, the type used for the result cast has the
precision and signedness of the given bit-field, rather than precision and signedness
of the underlying type.
</p>
<p>For example, the following macro can be used to portably check, at
compile-time, whether or not adding two constant integers will overflow,
and perform the addition only when it is known to be safe and not to trigger
a <samp>-Woverflow</samp> warning.
</p>
<div class="smallexample">
<pre class="smallexample">#define INT_ADD_OVERFLOW_P(a, b) \
   __builtin_add_overflow_p (a, b, (__typeof__ ((a) + (b))) 0)

enum {
    A = INT_MAX, B = 3,
    C = INT_ADD_OVERFLOW_P (A, B) ? 0 : A + B,
    D = __builtin_add_overflow_p (1, SCHAR_MAX, (signed char) 0)
};
</pre></div>

<p>The compiler will attempt to use hardware instructions to implement
these built-in functions where possible, like conditional jump on overflow
after addition, conditional jump on carry etc.
</p> 
</dd></dl>

<hr>
<div class="header">
<p>
Next: <a href="x86-specific-memory-model-extensions-for-transactional-memory.html#x86-specific-memory-model-extensions-for-transactional-memory" accesskey="n" rel="next">x86 specific memory model extensions for transactional memory</a>, Previous: <a href="_005f_005fatomic-Builtins.html#g_t_005f_005fatomic-Builtins" accesskey="p" rel="prev">__atomic Builtins</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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