| Daniel Dunbar | b3a6901 | 2009-06-26 16:47:03 +0000 | [diff] [blame^] | 1 | //===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===// |
| 2 | // |
| 3 | // The LLVM Compiler Infrastructure |
| 4 | // |
| 5 | // This file is distributed under the University of Illinois Open Source |
| 6 | // License. See LICENSE.TXT for details. |
| 7 | // |
| 8 | //===----------------------------------------------------------------------===// |
| 9 | // |
| 10 | // This file implements __popcountsi2 for the compiler_rt library. |
| 11 | // |
| 12 | //===----------------------------------------------------------------------===// |
| 13 | |
| 14 | #include "int_lib.h" |
| 15 | |
| 16 | // Returns: count of 1 bits |
| 17 | |
| 18 | si_int |
| 19 | __popcountsi2(si_int a) |
| 20 | { |
| 21 | su_int x = (su_int)a; |
| 22 | x = x - ((x >> 1) & 0x55555555); |
| 23 | // Every 2 bits holds the sum of every pair of bits |
| 24 | x = ((x >> 2) & 0x33333333) + (x & 0x33333333); |
| 25 | // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) |
| 26 | x = (x + (x >> 4)) & 0x0F0F0F0F; |
| 27 | // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) |
| 28 | x = (x + (x >> 16)); |
| 29 | // The lower 16 bits hold two 8 bit sums (5 significant bits). |
| 30 | // Upper 16 bits are garbage |
| 31 | return (x + (x >> 8)) & 0x0000003F; // (6 significant bits) |
| 32 | } |