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 } 34
