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| <title>Using the GNU Compiler Collection (GCC): Integer Overflow Builtins</title> |
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| <a name="Integer-Overflow-Builtins"></a> |
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| <a name="Built_002din-Functions-to-Perform-Arithmetic-with-Overflow-Checking"></a> |
| <h3 class="section">6.52 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 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 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 integer 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 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 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 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 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> |
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