//===-- popcountsi2.c - Implement __popcountsi2 ---------------------------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// // // This file implements __popcountsi2 for the compiler_rt library. // //===----------------------------------------------------------------------===// #include "int_lib.h" // Returns: count of 1 bits COMPILER_RT_ABI int __popcountsi2(si_int a) { su_int x = (su_int)a; x = x - ((x >> 1) & 0x55555555); // Every 2 bits holds the sum of every pair of bits x = ((x >> 2) & 0x33333333) + (x & 0x33333333); // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) x = (x + (x >> 4)) & 0x0F0F0F0F; // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) x = (x + (x >> 16)); // The lower 16 bits hold two 8 bit sums (5 significant bits). // Upper 16 bits are garbage return (x + (x >> 8)) & 0x0000003F; // (6 significant bits) } |