diff options
author | Eric Christopher <echristo@apple.com> | 2011-06-17 20:17:05 +0000 |
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committer | Eric Christopher <echristo@apple.com> | 2011-06-17 20:17:05 +0000 |
commit | 1ace4055f79f304750839d73c46bbcaeb994f1b5 (patch) | |
tree | 726c372193dcada5b3959cf02297889904c0e65c /lib/mulodi4.c | |
parent | 90467a679a4e45c035b126701a0450857f3c4483 (diff) |
Implement mulo<mode>4 for use in signed overflow checking.
Fixes rdar://9219742 and rdar://9218244
git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@133284 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/mulodi4.c')
-rw-r--r-- | lib/mulodi4.c | 59 |
1 files changed, 59 insertions, 0 deletions
diff --git a/lib/mulodi4.c b/lib/mulodi4.c new file mode 100644 index 000000000..dcaf6ab86 --- /dev/null +++ b/lib/mulodi4.c @@ -0,0 +1,59 @@ +/*===-- mulodi4.c - Implement __mulodi4 -----------------------------------=== + * + * 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 __mulodi4 for the compiler_rt library. + * + * ===----------------------------------------------------------------------=== + */ + +#include "int_lib.h" +#include <stdlib.h> + +/* Returns: a * b */ + +/* Effects: sets *overflow to 1 if a * b overflows */ + +di_int +__mulodi4(di_int a, di_int b, int* overflow) +{ + const int N = (int)(sizeof(di_int) * CHAR_BIT); + const di_int MIN = (di_int)1 << (N-1); + const di_int MAX = ~MIN; + *overflow = 0; + di_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; + } + di_int sa = a >> (N - 1); + di_int abs_a = (a ^ sa) - sa; + di_int sb = b >> (N - 1); + di_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; +} |