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/*===-- mulosi4.c - Implement __mulosi4 -----------------------------------===
*
* The LLVM Compiler Infrastructure
*
* This file is dual licensed under the MIT and the University of Illinois Open
* Source Licenses. See LICENSE.TXT for details.
*
* ===----------------------------------------------------------------------===
*
* This file implements __mulosi4 for the compiler_rt library.
*
* ===----------------------------------------------------------------------===
*/
#include "int_lib.h"
/* Returns: a * b */
/* Effects: sets *overflow to 1 if a * b overflows */
COMPILER_RT_ABI si_int
__mulosi4(si_int a, si_int b, int* overflow)
{
const int N = (int)(sizeof(si_int) * CHAR_BIT);
const si_int MIN = (si_int)1 << (N-1);
const si_int MAX = ~MIN;
*overflow = 0;
si_int result = a * b;
if (a == MIN)
{
if (b != 0 && b != 1)
*overflow = 1;
return result;
}
if (b == MIN)
{
if (a != 0 && a != 1)
*overflow = 1;
return result;
}
si_int sa = a >> (N - 1);
si_int abs_a = (a ^ sa) - sa;
si_int sb = b >> (N - 1);
si_int abs_b = (b ^ sb) - sb;
if (abs_a < 2 || abs_b < 2)
return result;
if (sa == sb)
{
if (abs_a > MAX / abs_b)
*overflow = 1;
}
else
{
if (abs_a > MIN / -abs_b)
*overflow = 1;
}
return result;
}
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