llvm-project
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1//===-- popcountti2.c - Implement __popcountti2
2//----------------------------===//
3//
4// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5// See https://llvm.org/LICENSE.txt for license information.
6// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements __popcountti2 for the compiler_rt library.
11//
12//===----------------------------------------------------------------------===//
13
14#include "int_lib.h"15
16#ifdef CRT_HAS_128BIT17
18// Returns: count of 1 bits
19
20COMPILER_RT_ABI int __popcountti2(ti_int a) {21tu_int x3 = (tu_int)a;22x3 = x3 - ((x3 >> 1) &23(((tu_int)0x5555555555555555uLL << 64) | 0x5555555555555555uLL));24// Every 2 bits holds the sum of every pair of bits (64)25x3 = ((x3 >> 2) &26(((tu_int)0x3333333333333333uLL << 64) | 0x3333333333333333uLL)) +27(x3 & (((tu_int)0x3333333333333333uLL << 64) | 0x3333333333333333uLL));28// Every 4 bits holds the sum of every 4-set of bits (3 significant bits) (32)29x3 = (x3 + (x3 >> 4)) &30(((tu_int)0x0F0F0F0F0F0F0F0FuLL << 64) | 0x0F0F0F0F0F0F0F0FuLL);31// Every 8 bits holds the sum of every 8-set of bits (4 significant bits) (16)32du_int x2 = (du_int)(x3 + (x3 >> 64));33// Every 8 bits holds the sum of every 8-set of bits (5 significant bits) (8)34su_int x = (su_int)(x2 + (x2 >> 32));35// Every 8 bits holds the sum of every 8-set of bits (6 significant bits) (4)36x = x + (x >> 16);37// Every 8 bits holds the sum of every 8-set of bits (7 significant bits) (2)38//39// Upper 16 bits are garbage40return (x + (x >> 8)) & 0xFF; // (8 significant bits)41}
42
43#endif // CRT_HAS_128BIT44