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 | |
21 | COMPILER_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 | |