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1//===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8//9// This file implements __popcountsi2 for the compiler_rt library.10//11//===----------------------------------------------------------------------===//12 13#include "int_lib.h"14 15// Returns: count of 1 bits16 17COMPILER_RT_ABI int __popcountsi2(si_int a) {18 su_int x = (su_int)a;19 x = x - ((x >> 1) & 0x55555555);20 // Every 2 bits holds the sum of every pair of bits21 x = ((x >> 2) & 0x33333333) + (x & 0x33333333);22 // Every 4 bits holds the sum of every 4-set of bits (3 significant bits)23 x = (x + (x >> 4)) & 0x0F0F0F0F;24 // Every 8 bits holds the sum of every 8-set of bits (4 significant bits)25 x = (x + (x >> 16));26 // The lower 16 bits hold two 8 bit sums (5 significant bits).27 // Upper 16 bits are garbage28 return (x + (x >> 8)) & 0x0000003F; // (6 significant bits)29}30