1276789Sdim/* ===-- popcountsi2.c - Implement __popcountsi2 ---------------------------=== 2276789Sdim * 3276789Sdim * The LLVM Compiler Infrastructure 4276789Sdim * 5276789Sdim * This file is dual licensed under the MIT and the University of Illinois Open 6276789Sdim * Source Licenses. See LICENSE.TXT for details. 7276789Sdim * 8276789Sdim * ===----------------------------------------------------------------------=== 9276789Sdim * 10276789Sdim * This file implements __popcountsi2 for the compiler_rt library. 11276789Sdim * 12276789Sdim * ===----------------------------------------------------------------------=== 13276789Sdim */ 14276789Sdim 15276789Sdim#include "int_lib.h" 16276789Sdim 17276789Sdim/* Returns: count of 1 bits */ 18276789Sdim 19276789SdimCOMPILER_RT_ABI si_int 20276789Sdim__popcountsi2(si_int a) 21276789Sdim{ 22276789Sdim su_int x = (su_int)a; 23276789Sdim x = x - ((x >> 1) & 0x55555555); 24276789Sdim /* Every 2 bits holds the sum of every pair of bits */ 25276789Sdim x = ((x >> 2) & 0x33333333) + (x & 0x33333333); 26276789Sdim /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) */ 27276789Sdim x = (x + (x >> 4)) & 0x0F0F0F0F; 28276789Sdim /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) */ 29276789Sdim x = (x + (x >> 16)); 30276789Sdim /* The lower 16 bits hold two 8 bit sums (5 significant bits).*/ 31276789Sdim /* Upper 16 bits are garbage */ 32276789Sdim return (x + (x >> 8)) & 0x0000003F; /* (6 significant bits) */ 33276789Sdim} 34