Eric Christopher | 1ace405 | 2011-06-17 20:17:05 +0000 | [diff] [blame] | 1 | /*===-- muloti4.c - Implement __muloti4 -----------------------------------=== |
| 2 | * |
| 3 | * The LLVM Compiler Infrastructure |
| 4 | * |
| 5 | * This file is dual licensed under the MIT and the University of Illinois Open |
| 6 | * Source Licenses. See LICENSE.TXT for details. |
| 7 | * |
| 8 | * ===----------------------------------------------------------------------=== |
| 9 | * |
| 10 | * This file implements __muloti4 for the compiler_rt library. |
| 11 | * |
| 12 | * ===----------------------------------------------------------------------=== |
| 13 | */ |
| 14 | |
Eric Christopher | 1ace405 | 2011-06-17 20:17:05 +0000 | [diff] [blame] | 15 | #include "int_lib.h" |
Eric Christopher | 1ace405 | 2011-06-17 20:17:05 +0000 | [diff] [blame] | 16 | |
Chandler Carruth | 7f2d7c7 | 2012-06-22 21:09:22 +0000 | [diff] [blame] | 17 | #if __x86_64 |
| 18 | |
Eric Christopher | 1ace405 | 2011-06-17 20:17:05 +0000 | [diff] [blame] | 19 | /* Returns: a * b */ |
| 20 | |
| 21 | /* Effects: sets *overflow to 1 if a * b overflows */ |
| 22 | |
| 23 | ti_int |
| 24 | __muloti4(ti_int a, ti_int b, int* overflow) |
| 25 | { |
| 26 | const int N = (int)(sizeof(ti_int) * CHAR_BIT); |
| 27 | const ti_int MIN = (ti_int)1 << (N-1); |
| 28 | const ti_int MAX = ~MIN; |
| 29 | *overflow = 0; |
| 30 | ti_int result = a * b; |
| 31 | if (a == MIN) |
| 32 | { |
| 33 | if (b != 0 && b != 1) |
| 34 | *overflow = 1; |
| 35 | return result; |
| 36 | } |
| 37 | if (b == MIN) |
| 38 | { |
| 39 | if (a != 0 && a != 1) |
| 40 | *overflow = 1; |
| 41 | return result; |
| 42 | } |
| 43 | ti_int sa = a >> (N - 1); |
| 44 | ti_int abs_a = (a ^ sa) - sa; |
| 45 | ti_int sb = b >> (N - 1); |
| 46 | ti_int abs_b = (b ^ sb) - sb; |
| 47 | if (abs_a < 2 || abs_b < 2) |
| 48 | return result; |
| 49 | if (sa == sb) |
| 50 | { |
| 51 | if (abs_a > MAX / abs_b) |
| 52 | *overflow = 1; |
| 53 | } |
| 54 | else |
| 55 | { |
| 56 | if (abs_a > MIN / -abs_b) |
| 57 | *overflow = 1; |
| 58 | } |
| 59 | return result; |
| 60 | } |
| 61 | |
| 62 | #endif |