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89 lines
2.8 KiB
89 lines
2.8 KiB
// Copyright 2011 the V8 project authors. All rights reserved.
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following
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// disclaimer in the documentation and/or other materials provided
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// with the distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived
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// from this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#ifndef V8_MISC_INTRINSICS_H_
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#define V8_MISC_INTRINSICS_H_
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#include "../include/v8.h"
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#include "globals.h"
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namespace v8 {
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namespace internal {
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// Returns the index of the leading 1 bit, counting the least significant bit at
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// index 0. (1 << IntegerLog2(x)) is a mask for the most significant bit of x.
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// Result is undefined if input is zero.
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int IntegerLog2(uint32_t value);
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#if defined(__GNUC__)
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inline int IntegerLog2(uint32_t value) {
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return 31 - __builtin_clz(value);
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}
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#elif defined(_MSC_VER)
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#pragma intrinsic(_BitScanReverse)
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inline int IntegerLog2(uint32_t value) {
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unsigned long result; // NOLINT: MSVC intrinsic demands this type.
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_BitScanReverse(&result, value);
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return result;
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}
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#else
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// Default version using regular operations. Code taken from:
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// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
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inline int IntegerLog2(uint32_t value) {
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int result, shift;
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shift = (value > 0xFFFF) << 4;
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value >>= shift;
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result = shift;
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shift = (value > 0xFF) << 3;
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value >>= shift;
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result |= shift;
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shift = (value > 0xF) << 2;
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value >>= shift;
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result |= shift;
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shift = (value > 0x3) << 1;
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value >>= shift;
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result |= shift;
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result |= (value >> 1);
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return result;
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}
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#endif
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} } // namespace v8::internal
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#endif // V8_MISC_INTRINSICS_H_
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