1 //===-- popcountdi2.c - Implement __popcountdi2 ---------------------------===// 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-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file implements __popcountdi2 for the compiler_rt library. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "int_lib.h" 14 15 // Returns: count of 1 bits 16 17 COMPILER_RT_ABI int __popcountdi2(di_int a) { 18 du_int x2 = (du_int)a; 19 x2 = x2 - ((x2 >> 1) & 0x5555555555555555uLL); 20 // Every 2 bits holds the sum of every pair of bits (32) 21 x2 = ((x2 >> 2) & 0x3333333333333333uLL) + (x2 & 0x3333333333333333uLL); 22 // Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (16) 23 x2 = (x2 + (x2 >> 4)) & 0x0F0F0F0F0F0F0F0FuLL; 24 // Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (8) 25 su_int x = (su_int)(x2 + (x2 >> 32)); 26 // The lower 32 bits hold four 16 bit sums (5 significant bits). 27 // Upper 32 bits are garbage 28 x = x + (x >> 16); 29 // The lower 16 bits hold two 32 bit sums (6 significant bits). 30 // Upper 16 bits are garbage 31 return (x + (x >> 8)) & 0x0000007F; // (7 significant bits) 32 } 33