1*8a6a9560SDaniel Boulby //===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===// 2*8a6a9560SDaniel Boulby // 3*8a6a9560SDaniel Boulby // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4*8a6a9560SDaniel Boulby // See https://llvm.org/LICENSE.txt for license information. 5*8a6a9560SDaniel Boulby // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6*8a6a9560SDaniel Boulby // 7*8a6a9560SDaniel Boulby //===----------------------------------------------------------------------===// 8*8a6a9560SDaniel Boulby // 9*8a6a9560SDaniel Boulby // This file implements __popcountsi2 for the compiler_rt library. 10*8a6a9560SDaniel Boulby // 11*8a6a9560SDaniel Boulby //===----------------------------------------------------------------------===// 12162fc183SLionel Debieve 13162fc183SLionel Debieve #include "int_lib.h" 14162fc183SLionel Debieve 15*8a6a9560SDaniel Boulby // Returns: count of 1 bits 16162fc183SLionel Debieve 17*8a6a9560SDaniel Boulby COMPILER_RT_ABI int __popcountsi2(si_int a) { 18162fc183SLionel Debieve su_int x = (su_int)a; 19162fc183SLionel Debieve x = x - ((x >> 1) & 0x55555555); 20*8a6a9560SDaniel Boulby // Every 2 bits holds the sum of every pair of bits 21162fc183SLionel Debieve x = ((x >> 2) & 0x33333333) + (x & 0x33333333); 22*8a6a9560SDaniel Boulby // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) 23162fc183SLionel Debieve x = (x + (x >> 4)) & 0x0F0F0F0F; 24*8a6a9560SDaniel Boulby // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) 25162fc183SLionel Debieve x = (x + (x >> 16)); 26*8a6a9560SDaniel Boulby // The lower 16 bits hold two 8 bit sums (5 significant bits). 27*8a6a9560SDaniel Boulby // Upper 16 bits are garbage 28*8a6a9560SDaniel Boulby return (x + (x >> 8)) & 0x0000003F; // (6 significant bits) 29162fc183SLionel Debieve } 30