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diff --git a/share/doc/gcc/Integer-Overflow-Builtins.html b/share/doc/gcc/Integer-Overflow-Builtins.html new file mode 100644 index 0000000..5a7410f --- /dev/null +++ b/share/doc/gcc/Integer-Overflow-Builtins.html @@ -0,0 +1,196 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +Copyright (C) 1988-2023 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). 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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 <code>false</code>, otherwise they return <code>true</code>. 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 <code>false</code>, otherwise they return <code>true</code>. +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="previous">__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="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |