mulodi4.c revision 2d1fdb26e458c4ddc04155c1d421bced3ba90cd0 
1/*===-- mulodi4.c - Implement __mulodi4 -----------------------------------===
2 *
3 *                     The LLVM Compiler Infrastructure
4 *
5 * This file is dual licensed under the MIT and the University of Illinois Open
6 * Source Licenses. See LICENSE.TXT for details.
7 *
8 * ===----------------------------------------------------------------------===
9 *
10 * This file implements __mulodi4 for the compiler_rt library.
11 *
12 * ===----------------------------------------------------------------------===
13 */
14
15#include "int_lib.h"
16
17/* Returns: a * b */
18
19/* Effects: sets *overflow to 1  if a * b overflows */
20
21COMPILER_RT_ABI di_int
22__mulodi4(di_int a, di_int b, int* overflow)
23{
24    const int N = (int)(sizeof(di_int) * CHAR_BIT);
25    const di_int MIN = (di_int)1 << (N-1);
26    const di_int MAX = ~MIN;
27    *overflow = 0;
28    di_int result = a * b;
29    if (a == MIN)
30    {
31        if (b != 0 && b != 1)
32	    *overflow = 1;
33	return result;
34    }
35    if (b == MIN)
36    {
37        if (a != 0 && a != 1)
38	    *overflow = 1;
39        return result;
40    }
41    di_int sa = a >> (N - 1);
42    di_int abs_a = (a ^ sa) - sa;
43    di_int sb = b >> (N - 1);
44    di_int abs_b = (b ^ sb) - sb;
45    if (abs_a < 2 || abs_b < 2)
46        return result;
47    if (sa == sb)
48    {
49        if (abs_a > MAX / abs_b)
50            *overflow = 1;
51    }
52    else
53    {
54        if (abs_a > MIN / -abs_b)
55            *overflow = 1;
56    }
57    return result;
58}
59