| 1 | //===-- int_mulo_impl.inc - Implement __mulo[sdt]i4 ---------------*- C -*-===// |
|---|---|
| 2 | // |
| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| 4 | // See https://llvm.org/LICENSE.txt for license information. |
| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| 6 | // |
| 7 | //===----------------------------------------------------------------------===// |
| 8 | // |
| 9 | // Helper used by __mulosi4, __mulodi4 and __muloti4. |
| 10 | // |
| 11 | //===----------------------------------------------------------------------===// |
| 12 | |
| 13 | #include "int_lib.h" |
| 14 | |
| 15 | // Returns: a * b |
| 16 | |
| 17 | // Effects: sets *overflow to 1 if a * b overflows |
| 18 | |
| 19 | static __inline fixint_t __muloXi4(fixint_t a, fixint_t b, int *overflow) { |
| 20 | const int N = (int)(sizeof(fixint_t) * CHAR_BIT); |
| 21 | const fixint_t MIN = (fixint_t)((fixuint_t)1 << (N - 1)); |
| 22 | const fixint_t MAX = ~MIN; |
| 23 | *overflow = 0; |
| 24 | fixint_t result = (fixuint_t)a * b; |
| 25 | if (a == MIN) { |
| 26 | if (b != 0 && b != 1) |
| 27 | *overflow = 1; |
| 28 | return result; |
| 29 | } |
| 30 | if (b == MIN) { |
| 31 | if (a != 0 && a != 1) |
| 32 | *overflow = 1; |
| 33 | return result; |
| 34 | } |
| 35 | fixint_t sa = a >> (N - 1); |
| 36 | fixint_t abs_a = (a ^ sa) - sa; |
| 37 | fixint_t sb = b >> (N - 1); |
| 38 | fixint_t abs_b = (b ^ sb) - sb; |
| 39 | if (abs_a < 2 || abs_b < 2) |
| 40 | return result; |
| 41 | if (sa == sb) { |
| 42 | if (abs_a > MAX / abs_b) |
| 43 | *overflow = 1; |
| 44 | } else { |
| 45 | if (abs_a > MIN / -abs_b) |
| 46 | *overflow = 1; |
| 47 | } |
| 48 | return result; |
| 49 | } |
| 50 |