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// Copyright 2011 the V8 project authors. 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 V8_MISC_INTRINSICS_H_
#define V8_MISC_INTRINSICS_H_
#include "../include/v8.h"
#include "globals.h"
namespace v8 {
namespace internal {
// Returns the index of the leading 1 bit, counting the least significant bit at
// index 0. (1 << IntegerLog2(x)) is a mask for the most significant bit of x.
// Result is undefined if input is zero.
int IntegerLog2(uint32_t value);
#if defined(__GNUC__)
inline int IntegerLog2(uint32_t value) {
return 31 - __builtin_clz(value);
}
#elif defined(_MSC_VER)
#pragma intrinsic(_BitScanReverse)
inline int IntegerLog2(uint32_t value) {
unsigned long result; // NOLINT: MSVC intrinsic demands this type.
_BitScanReverse(&result, value);
return result;
}
#else
// Default version using regular operations. Code taken from:
// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
inline int IntegerLog2(uint32_t value) {
int result, shift;
shift = (value > 0xFFFF) << 4;
value >>= shift;
result = shift;
shift = (value > 0xFF) << 3;
value >>= shift;
result |= shift;
shift = (value > 0xF) << 2;
value >>= shift;
result |= shift;
shift = (value > 0x3) << 1;
value >>= shift;
result |= shift;
result |= (value >> 1);
return result;
}
#endif
} } // namespace v8::internal
#endif // V8_MISC_INTRINSICS_H_
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