xref: /freebsd/contrib/llvm-project/compiler-rt/lib/builtins/int_mulo_impl.inc (revision 9768746ba83efa02837c5b9c66348db6e900208f)
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
19static __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)1 << (N - 1);
22  const fixint_t MAX = ~MIN;
23  *overflow = 0;
24  fixint_t result = 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