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54 lines
1.7 KiB
54 lines
1.7 KiB
9 years ago
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/* Copyright (c) 2016 Baidu, Inc. All Rights Reserve.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License. */
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#pragma once
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#include <type_traits>
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namespace paddle {
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/**
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* From Facebook folly:
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* https://github.com/facebook/folly/blob/master/folly/Bits.h
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*
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* findLastSet: return the 1-based index of the highest bit set
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*
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* for x > 0:
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* \f[
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* findLastSet(x) = 1 + \floor*{\log_{2}x}
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* \f]
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*/
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template <class T>
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inline constexpr typename std::enable_if<(std::is_integral<T>::value &&
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std::is_unsigned<T>::value &&
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sizeof(T) <= sizeof(unsigned int)),
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unsigned int>::type
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findLastSet(T x) {
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return x ? 8 * sizeof(unsigned int) - __builtin_clz(x) : 0;
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}
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template <class T>
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inline constexpr
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typename std::enable_if<(std::is_integral<T>::value &&
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std::is_unsigned<T>::value &&
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sizeof(T) > sizeof(unsigned int) &&
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sizeof(T) <= sizeof(unsigned long)), // NOLINT
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unsigned int>::type
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findLastSet(T x) {
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return x ? 8 * sizeof(unsigned long) - __builtin_clzl(x) : 0; // NOLINT
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}
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} // namespace paddle
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