diff options
Diffstat (limited to 'lib/builtins/popcountsi2.c')
-rw-r--r-- | lib/builtins/popcountsi2.c | 52 |
1 files changed, 24 insertions, 28 deletions
diff --git a/lib/builtins/popcountsi2.c b/lib/builtins/popcountsi2.c index 44544ff49..75e592a77 100644 --- a/lib/builtins/popcountsi2.c +++ b/lib/builtins/popcountsi2.c @@ -1,33 +1,29 @@ -/* ===-- popcountsi2.c - Implement __popcountsi2 ---------------------------=== - * - * The LLVM Compiler Infrastructure - * - * This file is dual licensed under the MIT and the University of Illinois Open - * Source Licenses. See LICENSE.TXT for details. - * - * ===----------------------------------------------------------------------=== - * - * This file implements __popcountsi2 for the compiler_rt library. - * - * ===----------------------------------------------------------------------=== - */ +//===-- 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 */ +// Returns: count of 1 bits -COMPILER_RT_ABI si_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) */ +COMPILER_RT_ABI si_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) } |