1//===-- mulvti3.c - Implement __mulvti3 -----------------------------------===//
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 __mulvti3 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: aborts if a * b overflows
20
21COMPILER_RT_ABI ti_int __mulvti3(ti_int a, ti_int b) {
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  if (a == MIN) {
26    if (b == 0 || b == 1)
27      return a * b;
28    compilerrt_abort();
29  }
30  if (b == MIN) {
31    if (a == 0 || a == 1)
32      return a * b;
33    compilerrt_abort();
34  }
35  ti_int sa = a >> (N - 1);
36  ti_int abs_a = (a ^ sa) - sa;
37  ti_int sb = b >> (N - 1);
38  ti_int abs_b = (b ^ sb) - sb;
39  if (abs_a < 2 || abs_b < 2)
40    return a * b;
41  if (sa == sb) {
42    if (abs_a > MAX / abs_b)
43      compilerrt_abort();
44  } else {
45    if (abs_a > MIN / -abs_b)
46      compilerrt_abort();
47  }
48  return a * b;
49}
50
51#endif // CRT_HAS_128BIT
52