forked from OSchip/llvm-project
50 lines
1.3 KiB
C
50 lines
1.3 KiB
C
//===-- mulosi4.c - Implement __mulosi4 -----------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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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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#include "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 __mulosi4(si_int a, si_int b, int *overflow) {
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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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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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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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if (abs_a > MAX / abs_b)
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*overflow = 1;
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} else {
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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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