1*162fc183SLionel Debieve /* ===-- popcountsi2.c - Implement __popcountsi2 ---------------------------=== 2*162fc183SLionel Debieve * 3*162fc183SLionel Debieve * The LLVM Compiler Infrastructure 4*162fc183SLionel Debieve * 5*162fc183SLionel Debieve * This file is dual licensed under the MIT and the University of Illinois Open 6*162fc183SLionel Debieve * Source Licenses. See LICENSE.TXT for details. 7*162fc183SLionel Debieve * 8*162fc183SLionel Debieve * ===----------------------------------------------------------------------=== 9*162fc183SLionel Debieve * 10*162fc183SLionel Debieve * This file implements __popcountsi2 for the compiler_rt library. 11*162fc183SLionel Debieve * 12*162fc183SLionel Debieve * ===----------------------------------------------------------------------=== 13*162fc183SLionel Debieve */ 14*162fc183SLionel Debieve 15*162fc183SLionel Debieve #include "int_lib.h" 16*162fc183SLionel Debieve 17*162fc183SLionel Debieve /* Returns: count of 1 bits */ 18*162fc183SLionel Debieve 19*162fc183SLionel Debieve COMPILER_RT_ABI si_int 20*162fc183SLionel Debieve __popcountsi2(si_int a) 21*162fc183SLionel Debieve { 22*162fc183SLionel Debieve su_int x = (su_int)a; 23*162fc183SLionel Debieve x = x - ((x >> 1) & 0x55555555); 24*162fc183SLionel Debieve /* Every 2 bits holds the sum of every pair of bits */ 25*162fc183SLionel Debieve x = ((x >> 2) & 0x33333333) + (x & 0x33333333); 26*162fc183SLionel Debieve /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) */ 27*162fc183SLionel Debieve x = (x + (x >> 4)) & 0x0F0F0F0F; 28*162fc183SLionel Debieve /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) */ 29*162fc183SLionel Debieve x = (x + (x >> 16)); 30*162fc183SLionel Debieve /* The lower 16 bits hold two 8 bit sums (5 significant bits).*/ 31*162fc183SLionel Debieve /* Upper 16 bits are garbage */ 32*162fc183SLionel Debieve return (x + (x >> 8)) & 0x0000003F; /* (6 significant bits) */ 33*162fc183SLionel Debieve } 34