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 | |
23 | COMPILER_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 | |