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// Copyright 2011 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#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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