1//===-- muloti4.c - Implement __muloti4 -----------------------------------===//
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// This file implements __muloti4 for the compiler_rt library.
10//
11//===----------------------------------------------------------------------===//
12
13#include "int_lib.h"
14
15#ifdef CRT_HAS_128BIT
16
17// Returns: a * b
18
19// Effects: sets *overflow to 1  if a * b overflows
20
21COMPILER_RT_ABI ti_int __muloti4(ti_int a, ti_int b, int *overflow) {
22  const int N = (int)(sizeof(ti_int) * CHAR_BIT);
23  const ti_int MIN = (ti_int)1 << (N - 1);
24  const ti_int MAX = ~MIN;
25  *overflow = 0;
26  ti_int result = a * b;
27  if (a == MIN) {
28    if (b != 0 && b != 1)
29      *overflow = 1;
30    return result;
31  }
32  if (b == MIN) {
33    if (a != 0 && a != 1)
34      *overflow = 1;
35    return result;
36  }
37  ti_int sa = a >> (N - 1);
38  ti_int abs_a = (a ^ sa) - sa;
39  ti_int sb = b >> (N - 1);
40  ti_int abs_b = (b ^ sb) - sb;
41  if (abs_a < 2 || abs_b < 2)
42    return result;
43  if (sa == sb) {
44    if (abs_a > MAX / abs_b)
45      *overflow = 1;
46  } else {
47    if (abs_a > MIN / -abs_b)
48      *overflow = 1;
49  }
50  return result;
51}
52
53#endif // CRT_HAS_128BIT
54