Daniel Boulby | 318e7a5 | 2022-10-21 20:20:52 +0100 | [diff] [blame^] | 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 | //===----------------------------------------------------------------------===// |
Lionel Debieve | 236f7bd | 2019-10-02 09:52:11 +0200 | [diff] [blame] | 12 | |
| 13 | #include "int_lib.h" |
| 14 | |
Daniel Boulby | 318e7a5 | 2022-10-21 20:20:52 +0100 | [diff] [blame^] | 15 | // Returns: count of 1 bits |
Lionel Debieve | 236f7bd | 2019-10-02 09:52:11 +0200 | [diff] [blame] | 16 | |
Daniel Boulby | 318e7a5 | 2022-10-21 20:20:52 +0100 | [diff] [blame^] | 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) |
Lionel Debieve | 236f7bd | 2019-10-02 09:52:11 +0200 | [diff] [blame] | 29 | } |