muloti4.c revision 2d1fdb26e458c4ddc04155c1d421bced3ba90cd0 
1/*===-- muloti4.c - Implement __muloti4 -----------------------------------===
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 __muloti4 for the compiler_rt library.
11 *
12 * ===----------------------------------------------------------------------===
13 */
14
15#include "int_lib.h"
16
17#ifdef CRT_HAS_128BIT
18
19/* Returns: a * b */
20
21/* Effects: sets *overflow to 1  if a * b overflows */
22
23COMPILER_RT_ABI ti_int
24__muloti4(ti_int a, ti_int b, int* overflow)
25{
26    const int N = (int)(sizeof(ti_int) * CHAR_BIT);
27    const ti_int MIN = (ti_int)1 << (N-1);
28    const ti_int MAX = ~MIN;
29    *overflow = 0;
30    ti_int result = a * b;
31    if (a == MIN)
32    {
33        if (b != 0 && b != 1)
34	    *overflow = 1;
35	return result;
36    }
37    if (b == MIN)
38    {
39        if (a != 0 && a != 1)
40	    *overflow = 1;
41        return result;
42    }
43    ti_int sa = a >> (N - 1);
44    ti_int abs_a = (a ^ sa) - sa;
45    ti_int sb = b >> (N - 1);
46    ti_int abs_b = (b ^ sb) - sb;
47    if (abs_a < 2 || abs_b < 2)
48        return result;
49    if (sa == sb)
50    {
51        if (abs_a > MAX / abs_b)
52            *overflow = 1;
53    }
54    else
55    {
56        if (abs_a > MIN / -abs_b)
57            *overflow = 1;
58    }
59    return result;
60}
61
62#endif /* CRT_HAS_128BIT */
63