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Diffstat (limited to 'src/bits.h')
-rw-r--r-- | src/bits.h | 131 |
1 files changed, 0 insertions, 131 deletions
diff --git a/src/bits.h b/src/bits.h deleted file mode 100644 index 98ae5c4b7..000000000 --- a/src/bits.h +++ /dev/null @@ -1,131 +0,0 @@ -/* - * 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_bits_h -#define wasm_bits_h - -#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. - */ - -namespace wasm { - -// Only the specialized templates should be instantiated, getting -// a linker error with these functions means an unsupported type was used. - -template<typename T> inline int PopCount(T /* v */); -template<typename T> inline T BitReverse(T /* v */); -template<typename T> inline int CountTrailingZeroes(T /* v */); -template<typename T> inline int CountLeadingZeroes(T /* v */); - -// Convenience signed -> unsigned. It usually doesn't make much sense to use bit -// functions on signed types. -template <typename T> inline int PopCount(T v) { - return PopCount(typename std::make_unsigned<T>::type(v)); -} -template <typename T> inline int CountTrailingZeroes(T v) { - return CountTrailingZeroes(typename std::make_unsigned<T>::type(v)); -} -template <typename T> inline int CountLeadingZeroes(T v) { - return CountLeadingZeroes(typename std::make_unsigned<T>::type(v)); -} - -// Implementations for the above templates. - -template<> inline int PopCount<uint8_t>(uint8_t v) { - // Small table lookup. - static const uint8_t tbl[32] = { - 0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4, - 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5 - }; - return tbl[v & 0xf] + tbl[v >> 4]; -} -template<> inline int PopCount<uint16_t>(uint16_t v) { - return PopCount<uint8_t>(v & 0xff) + PopCount<uint8_t>(v >> 8); -} -template<> inline int PopCount<uint32_t>(uint32_t v) { - // See Stanford bithacks, counting bits set in parallel, "best method": - // http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel - v = v - ((v >> 1) & 0x55555555); - v = (v & 0x33333333) + ((v >> 2) & 0x33333333); - return (((v + (v >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24; -} -template<> inline int PopCount<uint64_t>(uint64_t v) { - return PopCount<uint32_t>((uint32_t)v) + PopCount<uint32_t>(v >> 32); -} - -template<> inline uint32_t BitReverse<uint32_t>(uint32_t v) { - // See Hacker's Delight, first edition, figure 7-1. - v = ((v & 0x55555555) << 1) | ((v >> 1) & 0x55555555); - v = ((v & 0x33333333) << 2) | ((v >> 2) & 0x33333333); - v = ((v & 0x0F0F0F0F) << 4) | ((v >> 4) & 0x0F0F0F0F); - v = (v << 24) | ((v & 0xFF00) << 8) | - ((v >> 8) & 0xFF00) | (v >> 24); - return v; -} - -template<> inline int CountTrailingZeroes<uint32_t>(uint32_t v) { - // See Stanford bithacks, count the consecutive zero bits (trailing) on the - // right with multiply and lookup: - // http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup - static const uint8_t tbl[32] = { - 0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8, - 31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9 - }; - return v ? - (int)tbl[((uint32_t)((v & -(int32_t)v) * 0x077CB531U)) >> 27] : - 32; -} - -template<> inline int CountTrailingZeroes<uint64_t>(uint64_t v) { - return (uint32_t)v ? CountTrailingZeroes<uint32_t>(v) - : 32 + CountTrailingZeroes<uint32_t>(v >> 32); -} - -template<> inline int CountLeadingZeroes<uint32_t>(uint32_t v) { - // See Stanford bithacks, find the log base 2 of an N-bit integer in - // O(lg(N)) operations with multiply and lookup: - // http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogDeBruijn - static const uint8_t tbl[32] = { - 31, 22, 30, 21, 18, 10, 29, 2, 20, 17, 15, 13, 9, 6, 28, 1, - 23, 19, 11, 3, 16, 14, 7, 24, 12, 4, 8, 25, 5, 26, 27, 0 - }; - v = v | (v >> 1); - v = v | (v >> 2); - v = v | (v >> 4); - v = v | (v >> 8); - v = v | (v >> 16); - return v ? - (int)tbl[((uint32_t)(v * 0x07C4ACDDU)) >> 27] : - 32; -} - -template<> inline int CountLeadingZeroes<uint64_t>(uint64_t v) { - return v >> 32 ? CountLeadingZeroes<uint32_t>(v >> 32) - : 32 + CountLeadingZeroes<uint32_t>(v); -} - -} // namespace wasm - -#endif // wasm_bits_h |