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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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#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 |
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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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} |