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1 | /* ===-- popcountdi2.c - Implement __popcountdi2 ----------------------------=== |
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 __popcountdi2 for the compiler_rt library. | |
11 | * | |
12 | * ===----------------------------------------------------------------------=== | |
13 | */ | |
14 | ||
15 | #include "int_lib.h" | |
16 | ||
17 | /* Returns: count of 1 bits */ | |
18 | ||
19 | COMPILER_RT_ABI si_int | |
20 | __popcountdi2(di_int a) | |
21 | { | |
22 | du_int x2 = (du_int)a; | |
23 | x2 = x2 - ((x2 >> 1) & 0x5555555555555555uLL); | |
24 | /* Every 2 bits holds the sum of every pair of bits (32) */ | |
25 | x2 = ((x2 >> 2) & 0x3333333333333333uLL) + (x2 & 0x3333333333333333uLL); | |
26 | /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (16) */ | |
27 | x2 = (x2 + (x2 >> 4)) & 0x0F0F0F0F0F0F0F0FuLL; | |
28 | /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (8) */ | |
29 | su_int x = (su_int)(x2 + (x2 >> 32)); | |
30 | /* The lower 32 bits hold four 16 bit sums (5 significant bits). */ | |
31 | /* Upper 32 bits are garbage */ | |
32 | x = x + (x >> 16); | |
33 | /* The lower 16 bits hold two 32 bit sums (6 significant bits). */ | |
34 | /* Upper 16 bits are garbage */ | |
35 | return (x + (x >> 8)) & 0x0000007F; /* (7 significant bits) */ | |
36 | } |