1*0b57cec5SDimitry Andric //===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===// 2*0b57cec5SDimitry Andric // 3*0b57cec5SDimitry Andric // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4*0b57cec5SDimitry Andric // See https://llvm.org/LICENSE.txt for license information. 5*0b57cec5SDimitry Andric // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6*0b57cec5SDimitry Andric // 7*0b57cec5SDimitry Andric //===----------------------------------------------------------------------===// 8*0b57cec5SDimitry Andric // 9*0b57cec5SDimitry Andric // This file implements __popcountsi2 for the compiler_rt library. 10*0b57cec5SDimitry Andric // 11*0b57cec5SDimitry Andric //===----------------------------------------------------------------------===// 12*0b57cec5SDimitry Andric 13*0b57cec5SDimitry Andric #include "int_lib.h" 14*0b57cec5SDimitry Andric 15*0b57cec5SDimitry Andric // Returns: count of 1 bits 16*0b57cec5SDimitry Andric 17*0b57cec5SDimitry Andric COMPILER_RT_ABI si_int __popcountsi2(si_int a) { 18*0b57cec5SDimitry Andric su_int x = (su_int)a; 19*0b57cec5SDimitry Andric x = x - ((x >> 1) & 0x55555555); 20*0b57cec5SDimitry Andric // Every 2 bits holds the sum of every pair of bits 21*0b57cec5SDimitry Andric x = ((x >> 2) & 0x33333333) + (x & 0x33333333); 22*0b57cec5SDimitry Andric // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) 23*0b57cec5SDimitry Andric x = (x + (x >> 4)) & 0x0F0F0F0F; 24*0b57cec5SDimitry Andric // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) 25*0b57cec5SDimitry Andric x = (x + (x >> 16)); 26*0b57cec5SDimitry Andric // The lower 16 bits hold two 8 bit sums (5 significant bits). 27*0b57cec5SDimitry Andric // Upper 16 bits are garbage 28*0b57cec5SDimitry Andric return (x + (x >> 8)) & 0x0000003F; // (6 significant bits) 29*0b57cec5SDimitry Andric } 30