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