13cab2bb3Spatrick //===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===// 23cab2bb3Spatrick // 33cab2bb3Spatrick // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 43cab2bb3Spatrick // See https://llvm.org/LICENSE.txt for license information. 53cab2bb3Spatrick // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 63cab2bb3Spatrick // 73cab2bb3Spatrick //===----------------------------------------------------------------------===// 83cab2bb3Spatrick // 93cab2bb3Spatrick // This file implements __popcountsi2 for the compiler_rt library. 103cab2bb3Spatrick // 113cab2bb3Spatrick //===----------------------------------------------------------------------===// 123cab2bb3Spatrick 133cab2bb3Spatrick #include "int_lib.h" 143cab2bb3Spatrick 153cab2bb3Spatrick // Returns: count of 1 bits 163cab2bb3Spatrick __popcountsi2(si_int a)17*1f9cb04fSpatrickCOMPILER_RT_ABI int __popcountsi2(si_int a) { 183cab2bb3Spatrick su_int x = (su_int)a; 193cab2bb3Spatrick x = x - ((x >> 1) & 0x55555555); 203cab2bb3Spatrick // Every 2 bits holds the sum of every pair of bits 213cab2bb3Spatrick x = ((x >> 2) & 0x33333333) + (x & 0x33333333); 223cab2bb3Spatrick // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) 233cab2bb3Spatrick x = (x + (x >> 4)) & 0x0F0F0F0F; 243cab2bb3Spatrick // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) 253cab2bb3Spatrick x = (x + (x >> 16)); 263cab2bb3Spatrick // The lower 16 bits hold two 8 bit sums (5 significant bits). 273cab2bb3Spatrick // Upper 16 bits are garbage 283cab2bb3Spatrick return (x + (x >> 8)) & 0x0000003F; // (6 significant bits) 293cab2bb3Spatrick } 30