1214152Sed/* ===-- popcountsi2.c - Implement __popcountsi2 ---------------------------=== 2214152Sed * 3214152Sed * The LLVM Compiler Infrastructure 4214152Sed * 5222656Sed * This file is dual licensed under the MIT and the University of Illinois Open 6222656Sed * Source Licenses. See LICENSE.TXT for details. 7214152Sed * 8214152Sed * ===----------------------------------------------------------------------=== 9214152Sed * 10214152Sed * This file implements __popcountsi2 for the compiler_rt library. 11214152Sed * 12214152Sed * ===----------------------------------------------------------------------=== 13214152Sed */ 14214152Sed 15214152Sed#include "int_lib.h" 16214152Sed 17214152Sed/* Returns: count of 1 bits */ 18214152Sed 19222656SedCOMPILER_RT_ABI si_int 20214152Sed__popcountsi2(si_int a) 21214152Sed{ 22214152Sed su_int x = (su_int)a; 23214152Sed x = x - ((x >> 1) & 0x55555555); 24214152Sed /* Every 2 bits holds the sum of every pair of bits */ 25214152Sed x = ((x >> 2) & 0x33333333) + (x & 0x33333333); 26214152Sed /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) */ 27214152Sed x = (x + (x >> 4)) & 0x0F0F0F0F; 28214152Sed /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) */ 29214152Sed x = (x + (x >> 16)); 30214152Sed /* The lower 16 bits hold two 8 bit sums (5 significant bits).*/ 31214152Sed /* Upper 16 bits are garbage */ 32214152Sed return (x + (x >> 8)) & 0x0000003F; /* (6 significant bits) */ 33214152Sed} 34