mirror of
https://github.com/flutter/flutter.git
synced 2026-02-20 02:29:02 +08:00
79 lines
2.9 KiB
C++
79 lines
2.9 KiB
C++
/*
|
|
* Copyright (C) 2013 Google Inc. All rights reserved.
|
|
*
|
|
* Redistribution and use in source and binary forms, with or without
|
|
* modification, are permitted provided that the following conditions are
|
|
* met:
|
|
*
|
|
* * Redistributions of source code must retain the above copyright
|
|
* notice, this list of conditions and the following disclaimer.
|
|
* * Redistributions in binary form must reproduce the above
|
|
* copyright notice, this list of conditions and the following disclaimer
|
|
* in the documentation and/or other materials provided with the
|
|
* distribution.
|
|
* * Neither the name of Google Inc. nor the names of its
|
|
* contributors may be used to endorse or promote products derived from
|
|
* this software without specific prior written permission.
|
|
*
|
|
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
|
|
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
|
|
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
|
|
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
|
|
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
|
|
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
|
|
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
|
|
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
|
|
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
|
|
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
|
|
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
|
|
*/
|
|
|
|
#ifndef SKY_ENGINE_WTF_BITWISEOPERATIONS_H_
|
|
#define SKY_ENGINE_WTF_BITWISEOPERATIONS_H_
|
|
|
|
// DESCRIPTION
|
|
// countLeadingZeros() is a bitwise operation that counts the number of leading
|
|
// zeros in a binary value, starting with the most significant bit. C does not
|
|
// have an operator to do this, but fortunately the various compilers have
|
|
// built-ins that map to fast underlying processor instructions.
|
|
|
|
#include "flutter/sky/engine/wtf/CPU.h"
|
|
#include "flutter/sky/engine/wtf/Compiler.h"
|
|
|
|
#include <stdint.h>
|
|
|
|
namespace WTF {
|
|
|
|
#if COMPILER(GCC)
|
|
|
|
// This is very annoying. __builtin_clz has undefined behaviour for an input of
|
|
// 0, even though these's clearly a return value that makes sense, and even
|
|
// though nascent processor clz instructions have defined behaviour for 0.
|
|
// We could drop to raw __asm__ to do better, but we'll avoid doing that unless
|
|
// we see proof that we need to.
|
|
ALWAYS_INLINE uint32_t countLeadingZeros32(uint32_t x)
|
|
{
|
|
return LIKELY(x) ? __builtin_clz(x) : 32;
|
|
}
|
|
|
|
ALWAYS_INLINE uint64_t countLeadingZeros64(uint64_t x)
|
|
{
|
|
return LIKELY(x) ? __builtin_clzll(x) : 64;
|
|
}
|
|
|
|
#endif
|
|
|
|
#if CPU(64BIT)
|
|
|
|
ALWAYS_INLINE size_t countLeadingZerosSizet(size_t x) { return countLeadingZeros64(x); }
|
|
|
|
#else
|
|
|
|
ALWAYS_INLINE size_t countLeadingZerosSizet(size_t x) { return countLeadingZeros32(x); }
|
|
|
|
#endif
|
|
|
|
} // namespace WTF
|
|
|
|
#endif // SKY_ENGINE_WTF_BITWISEOPERATIONS_H_
|