| Lionel Debieve | 236f7bd | 2019-10-02 09:52:11 +0200 | [diff] [blame] | 1 | /* ===-- popcountsi2.c - Implement __popcountsi2 ---------------------------=== |
| 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 __popcountsi2 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 | __popcountsi2(si_int a) |
| 21 | { |
| 22 | su_int x = (su_int)a; |
| 23 | x = x - ((x >> 1) & 0x55555555); |
| 24 | /* Every 2 bits holds the sum of every pair of bits */ |
| 25 | x = ((x >> 2) & 0x33333333) + (x & 0x33333333); |
| 26 | /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) */ |
| 27 | x = (x + (x >> 4)) & 0x0F0F0F0F; |
| 28 | /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) */ |
| 29 | x = (x + (x >> 16)); |
| 30 | /* The lower 16 bits hold two 8 bit sums (5 significant bits).*/ |
| 31 | /* Upper 16 bits are garbage */ |
| 32 | return (x + (x >> 8)) & 0x0000003F; /* (6 significant bits) */ |
| 33 | } |