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/*
* Copyright 2015 WebAssembly Community Group participants
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef wasm_support_bits_h
#define wasm_support_bits_h
#include <climits>
#include <cstdint>
#include <type_traits>
/*
* Portable bit functions.
*
* Not all platforms offer fast intrinsics for these functions, and some
* compilers require checking CPUID at runtime before using the intrinsic.
*
* We instead use portable and reasonably-fast implementations, while
* avoiding implementations with large lookup tables.
*
* TODO: The convention here should be changed PopCount => popCount,
* initial lowercase, to match the rest of the codebase.
*/
namespace wasm {
template<typename T> int PopCount(T);
template<typename T> uint32_t BitReverse(T);
template<typename T> int CountTrailingZeroes(T);
template<typename T> int CountLeadingZeroes(T);
#ifndef wasm_support_bits_definitions
// The template specializations are provided elsewhere.
extern template int PopCount(uint8_t);
extern template int PopCount(uint16_t);
extern template int PopCount(uint32_t);
extern template int PopCount(uint64_t);
extern template uint32_t BitReverse(uint32_t);
extern template int CountTrailingZeroes(uint32_t);
extern template int CountTrailingZeroes(uint64_t);
extern template int CountLeadingZeroes(uint32_t);
extern template int CountLeadingZeroes(uint64_t);
#endif
// Convenience signed -> unsigned. It usually doesn't make much sense to use bit
// functions on signed types.
template<typename T> int PopCount(T v) {
return PopCount(typename std::make_unsigned<T>::type(v));
}
template<typename T> int CountTrailingZeroes(T v) {
return CountTrailingZeroes(typename std::make_unsigned<T>::type(v));
}
template<typename T> int CountLeadingZeroes(T v) {
return CountLeadingZeroes(typename std::make_unsigned<T>::type(v));
}
template<typename T> bool IsPowerOf2(T v) { return v != 0 && PopCount(v) == 1; }
template<typename T, typename U> inline static T RotateLeft(T val, U count) {
T mask = sizeof(T) * CHAR_BIT - 1;
count &= mask;
return (val << count) | (val >> (-count & mask));
}
template<typename T, typename U> inline static T RotateRight(T val, U count) {
T mask = sizeof(T) * CHAR_BIT - 1;
count &= mask;
return (val >> count) | (val << (-count & mask));
}
extern uint32_t Log2(uint32_t v);
extern uint32_t Pow2(uint32_t v);
} // namespace wasm
#endif // wasm_support_bits_h
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