You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
194 lines
13 KiB
HTML
194 lines
13 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
|
|
|
|
Permission is granted to copy, distribute and/or modify this document
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
|
any later version published by the Free Software Foundation; with the
|
|
Invariant Sections being "Funding Free Software", the Front-Cover
|
|
Texts being (a) (see below), and with the Back-Cover Texts being (b)
|
|
(see below). A copy of the license is included in the section entitled
|
|
"GNU Free Documentation License".
|
|
|
|
(a) The FSF's Front-Cover Text is:
|
|
|
|
A GNU Manual
|
|
|
|
(b) The FSF's Back-Cover Text is:
|
|
|
|
You have freedom to copy and modify this GNU Manual, like GNU
|
|
software. Copies published by the Free Software Foundation raise
|
|
funds for GNU development. -->
|
|
<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<title>Integer Overflow Builtins (Using the GNU Compiler Collection (GCC))</title>
|
|
|
|
<meta name="description" content="Integer Overflow Builtins (Using the GNU Compiler Collection (GCC))">
|
|
<meta name="keywords" content="Integer Overflow Builtins (Using the GNU Compiler Collection (GCC))">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content="makeinfo">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<link href="index.html#Top" rel="start" title="Top">
|
|
<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="C-Extensions.html#C-Extensions" rel="up" title="C Extensions">
|
|
<link href="x86-specific-memory-model-extensions-for-transactional-memory.html#x86-specific-memory-model-extensions-for-transactional-memory" rel="next" title="x86 specific memory model extensions for transactional memory">
|
|
<link href="_005f_005fatomic-Builtins.html#g_t_005f_005fatomic-Builtins" rel="prev" title="__atomic Builtins">
|
|
<style type="text/css">
|
|
<!--
|
|
a.summary-letter {text-decoration: none}
|
|
blockquote.indentedblock {margin-right: 0em}
|
|
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
|
|
blockquote.smallquotation {font-size: smaller}
|
|
div.display {margin-left: 3.2em}
|
|
div.example {margin-left: 3.2em}
|
|
div.lisp {margin-left: 3.2em}
|
|
div.smalldisplay {margin-left: 3.2em}
|
|
div.smallexample {margin-left: 3.2em}
|
|
div.smalllisp {margin-left: 3.2em}
|
|
kbd {font-style: oblique}
|
|
pre.display {font-family: inherit}
|
|
pre.format {font-family: inherit}
|
|
pre.menu-comment {font-family: serif}
|
|
pre.menu-preformatted {font-family: serif}
|
|
pre.smalldisplay {font-family: inherit; font-size: smaller}
|
|
pre.smallexample {font-size: smaller}
|
|
pre.smallformat {font-family: inherit; font-size: smaller}
|
|
pre.smalllisp {font-size: smaller}
|
|
span.nolinebreak {white-space: nowrap}
|
|
span.roman {font-family: initial; font-weight: normal}
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
|
ul.no-bullet {list-style: none}
|
|
-->
|
|
</style>
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en">
|
|
<a name="Integer-Overflow-Builtins"></a>
|
|
<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> [<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>
|
|
</div>
|
|
<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’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> [<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>
|
|
</div>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|