1//===-- mulvsi3.c - Implement __mulvsi3 -----------------------------------===//
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 __mulvsi3 for the compiler_rt library.
10//
11//===----------------------------------------------------------------------===//
12
13#include "int_lib.h"
14
15// Returns: a * b
16
17// Effects: aborts if a * b overflows
18
19COMPILER_RT_ABI si_int __mulvsi3(si_int a, si_int b) {
20  const int N = (int)(sizeof(si_int) * CHAR_BIT);
21  const si_int MIN = (si_int)1 << (N - 1);
22  const si_int MAX = ~MIN;
23  if (a == MIN) {
24    if (b == 0 || b == 1)
25      return a * b;
26    compilerrt_abort();
27  }
28  if (b == MIN) {
29    if (a == 0 || a == 1)
30      return a * b;
31    compilerrt_abort();
32  }
33  si_int sa = a >> (N - 1);
34  si_int abs_a = (a ^ sa) - sa;
35  si_int sb = b >> (N - 1);
36  si_int abs_b = (b ^ sb) - sb;
37  if (abs_a < 2 || abs_b < 2)
38    return a * b;
39  if (sa == sb) {
40    if (abs_a > MAX / abs_b)
41      compilerrt_abort();
42  } else {
43    if (abs_a > MIN / -abs_b)
44      compilerrt_abort();
45  }
46  return a * b;
47}
48