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-exception
6 //
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 bits
16
__popcountsi2(si_int a)17 COMPILER_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 bits
21 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 garbage
28 return (x + (x >> 8)) & 0x0000003F; // (6 significant bits)
29 }
30