multi3.c revision 2d1fdb26e458c4ddc04155c1d421bced3ba90cd0 
1/* ===-- multi3.c - Implement __multi3 -------------------------------------===
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 __multi3 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
21static
22ti_int
23__mulddi3(du_int a, du_int b)
24{
25    twords r;
26    const int bits_in_dword_2 = (int)(sizeof(di_int) * CHAR_BIT) / 2;
27    const du_int lower_mask = (du_int)~0 >> bits_in_dword_2;
28    r.s.low = (a & lower_mask) * (b & lower_mask);
29    du_int t = r.s.low >> bits_in_dword_2;
30    r.s.low &= lower_mask;
31    t += (a >> bits_in_dword_2) * (b & lower_mask);
32    r.s.low += (t & lower_mask) << bits_in_dword_2;
33    r.s.high = t >> bits_in_dword_2;
34    t = r.s.low >> bits_in_dword_2;
35    r.s.low &= lower_mask;
36    t += (b >> bits_in_dword_2) * (a & lower_mask);
37    r.s.low += (t & lower_mask) << bits_in_dword_2;
38    r.s.high += t >> bits_in_dword_2;
39    r.s.high += (a >> bits_in_dword_2) * (b >> bits_in_dword_2);
40    return r.all;
41}
42
43/* Returns: a * b */
44
45COMPILER_RT_ABI ti_int
46__multi3(ti_int a, ti_int b)
47{
48    twords x;
49    x.all = a;
50    twords y;
51    y.all = b;
52    twords r;
53    r.all = __mulddi3(x.s.low, y.s.low);
54    r.s.high += x.s.high * y.s.low + x.s.low * y.s.high;
55    return r.all;
56}
57
58#endif /* CRT_HAS_128BIT */
59