1*0a6a1f1dSLionel Sambuc /* ===-- popcountsi2.c - Implement __popcountsi2 ---------------------------=== 2*0a6a1f1dSLionel Sambuc * 3*0a6a1f1dSLionel Sambuc * The LLVM Compiler Infrastructure 4*0a6a1f1dSLionel Sambuc * 5*0a6a1f1dSLionel Sambuc * This file is dual licensed under the MIT and the University of Illinois Open 6*0a6a1f1dSLionel Sambuc * Source Licenses. See LICENSE.TXT for details. 7*0a6a1f1dSLionel Sambuc * 8*0a6a1f1dSLionel Sambuc * ===----------------------------------------------------------------------=== 9*0a6a1f1dSLionel Sambuc * 10*0a6a1f1dSLionel Sambuc * This file implements __popcountsi2 for the compiler_rt library. 11*0a6a1f1dSLionel Sambuc * 12*0a6a1f1dSLionel Sambuc * ===----------------------------------------------------------------------=== 13*0a6a1f1dSLionel Sambuc */ 14*0a6a1f1dSLionel Sambuc 15*0a6a1f1dSLionel Sambuc #include "int_lib.h" 16*0a6a1f1dSLionel Sambuc 17*0a6a1f1dSLionel Sambuc /* Returns: count of 1 bits */ 18*0a6a1f1dSLionel Sambuc 19*0a6a1f1dSLionel Sambuc COMPILER_RT_ABI si_int __popcountsi2(si_int a)20*0a6a1f1dSLionel Sambuc__popcountsi2(si_int a) 21*0a6a1f1dSLionel Sambuc { 22*0a6a1f1dSLionel Sambuc su_int x = (su_int)a; 23*0a6a1f1dSLionel Sambuc x = x - ((x >> 1) & 0x55555555); 24*0a6a1f1dSLionel Sambuc /* Every 2 bits holds the sum of every pair of bits */ 25*0a6a1f1dSLionel Sambuc x = ((x >> 2) & 0x33333333) + (x & 0x33333333); 26*0a6a1f1dSLionel Sambuc /* Every 4 bits holds the sum of every 4-set of bits (3 significant bits) */ 27*0a6a1f1dSLionel Sambuc x = (x + (x >> 4)) & 0x0F0F0F0F; 28*0a6a1f1dSLionel Sambuc /* Every 8 bits holds the sum of every 8-set of bits (4 significant bits) */ 29*0a6a1f1dSLionel Sambuc x = (x + (x >> 16)); 30*0a6a1f1dSLionel Sambuc /* The lower 16 bits hold two 8 bit sums (5 significant bits).*/ 31*0a6a1f1dSLionel Sambuc /* Upper 16 bits are garbage */ 32*0a6a1f1dSLionel Sambuc return (x + (x >> 8)) & 0x0000003F; /* (6 significant bits) */ 33*0a6a1f1dSLionel Sambuc } 34