10b57cec5SDimitry Andric //===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===// 20b57cec5SDimitry Andric // 30b57cec5SDimitry Andric // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 40b57cec5SDimitry Andric // See https://llvm.org/LICENSE.txt for license information. 50b57cec5SDimitry Andric // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 60b57cec5SDimitry Andric // 70b57cec5SDimitry Andric //===----------------------------------------------------------------------===// 80b57cec5SDimitry Andric // 90b57cec5SDimitry Andric // This file implements __popcountsi2 for the compiler_rt library. 100b57cec5SDimitry Andric // 110b57cec5SDimitry Andric //===----------------------------------------------------------------------===// 120b57cec5SDimitry Andric 130b57cec5SDimitry Andric #include "int_lib.h" 140b57cec5SDimitry Andric 150b57cec5SDimitry Andric // Returns: count of 1 bits 160b57cec5SDimitry Andric __popcountsi2(si_int a)17*5ffd83dbSDimitry AndricCOMPILER_RT_ABI int __popcountsi2(si_int a) { 180b57cec5SDimitry Andric su_int x = (su_int)a; 190b57cec5SDimitry Andric x = x - ((x >> 1) & 0x55555555); 200b57cec5SDimitry Andric // Every 2 bits holds the sum of every pair of bits 210b57cec5SDimitry Andric x = ((x >> 2) & 0x33333333) + (x & 0x33333333); 220b57cec5SDimitry Andric // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) 230b57cec5SDimitry Andric x = (x + (x >> 4)) & 0x0F0F0F0F; 240b57cec5SDimitry Andric // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) 250b57cec5SDimitry Andric x = (x + (x >> 16)); 260b57cec5SDimitry Andric // The lower 16 bits hold two 8 bit sums (5 significant bits). 270b57cec5SDimitry Andric // Upper 16 bits are garbage 280b57cec5SDimitry Andric return (x + (x >> 8)) & 0x0000003F; // (6 significant bits) 290b57cec5SDimitry Andric } 30