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Bitmap: Extract common bit operations like GetBit and SetBitTo (apach…
…e#2105) This is a refactor, see: apache#2076 Previously, adhoc bit operations are used. This patch extract `GetBit` and `SetBitTo` operation to simplify the impl. Also, because the LSB/MSB format we're using it different in BitmapString and Bitmap( see apache/kvrocks-website#198 ), `lsb` and `msb` is extracted to prevent from mistakes.
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| /* | ||
| * Licensed to the Apache Software Foundation (ASF) under one | ||
| * or more contributor license agreements. See the NOTICE file | ||
| * distributed with this work for additional information | ||
| * regarding copyright ownership. The ASF licenses this file | ||
| * to you 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. | ||
| * | ||
| */ | ||
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| #pragma once | ||
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| namespace util { | ||
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| /* Count number of bits set in the binary array pointed by 's' and long | ||
| * 'count' bytes. The implementation of this function is required to | ||
| * work with a input string length up to 512 MB. | ||
| * */ | ||
| inline size_t RawPopcount(const uint8_t *p, int64_t count) { | ||
| size_t bits = 0; | ||
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| for (; count >= 8; p += 8, count -= 8) { | ||
| bits += __builtin_popcountll(*reinterpret_cast<const uint64_t *>(p)); | ||
| } | ||
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| if (count > 0) { | ||
| uint64_t v = 0; | ||
| __builtin_memcpy(&v, p, count); | ||
| bits += __builtin_popcountll(v); | ||
| } | ||
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| return bits; | ||
| } | ||
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| template <typename T = void> | ||
| inline int ClzllWithEndian(uint64_t x) { | ||
| if constexpr (IsLittleEndian()) { | ||
| return __builtin_clzll(__builtin_bswap64(x)); | ||
| } else if constexpr (IsBigEndian()) { | ||
| return __builtin_clzll(x); | ||
| } else { | ||
| static_assert(AlwaysFalse<T>); | ||
| } | ||
| } | ||
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| // Return the number of bytes needed to fit the given number of bits | ||
| constexpr int64_t BytesForBits(int64_t bits) { | ||
| // This formula avoids integer overflow on very large `bits` | ||
| return (bits >> 3) + ((bits & 7) != 0); | ||
| } | ||
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| namespace lsb { | ||
| static constexpr bool GetBit(const uint8_t *bits, uint64_t i) { return (bits[i >> 3] >> (i & 0x07)) & 1; } | ||
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| // Bitmask selecting the k-th bit in a byte | ||
| static constexpr uint8_t kBitmask[] = {1, 2, 4, 8, 16, 32, 64, 128}; | ||
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| // Gets the i-th bit from a byte. Should only be used with i <= 7. | ||
| static constexpr bool GetBitFromByte(uint8_t byte, uint8_t i) { return byte & kBitmask[i]; } | ||
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| static inline void SetBitTo(uint8_t *bits, int64_t i, bool bit_is_set) { | ||
| // https://graphics.stanford.edu/~seander/bithacks.html | ||
| // "Conditionally set or clear bits without branching" | ||
| // NOTE: this seems to confuse Valgrind as it reads from potentially | ||
| // uninitialized memory | ||
| bits[i / 8] ^= static_cast<uint8_t>(-static_cast<uint8_t>(bit_is_set) ^ bits[i / 8]) & kBitmask[i % 8]; | ||
| } | ||
| } // namespace lsb | ||
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| namespace msb { | ||
| static constexpr bool GetBit(const uint8_t *bits, uint64_t i) { return (bits[i >> 3] >> (7 - (i & 0x07))) & 1; } | ||
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| // Bitmask selecting the k-th bit in a byte | ||
| static constexpr uint8_t kBitmask[] = {128, 64, 32, 16, 8, 4, 2, 1}; | ||
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| // Gets the i-th bit from a byte. Should only be used with i <= 7. | ||
| static constexpr bool GetBitFromByte(uint8_t byte, uint8_t i) { return byte & kBitmask[i]; } | ||
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| static inline void SetBitTo(uint8_t *bits, int64_t i, bool bit_is_set) { | ||
| // https://graphics.stanford.edu/~seander/bithacks.html | ||
| // "Conditionally set or clear bits without branching" | ||
| // NOTE: this seems to confuse Valgrind as it reads from potentially | ||
| // uninitialized memory | ||
| bits[i / 8] ^= static_cast<uint8_t>(-static_cast<uint8_t>(bit_is_set) ^ bits[i / 8]) & kBitmask[i % 8]; | ||
| } | ||
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| /* Return the position of the first bit set to one (if 'bit' is 1) or | ||
| * zero (if 'bit' is 0) in the bitmap starting at 's' and long 'count' bytes. | ||
| * | ||
| * The function is guaranteed to return a value >= 0 if 'bit' is 0 since if | ||
| * no zero bit is found, it returns count*8 assuming the string is zero | ||
| * padded on the right. However if 'bit' is 1 it is possible that there is | ||
| * not a single set bit in the bitmap. In this special case -1 is returned. | ||
| * */ | ||
| inline int64_t RawBitpos(const uint8_t *c, int64_t count, bool bit) { | ||
| int64_t res = 0; | ||
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| if (bit) { | ||
| int64_t ct = count; | ||
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| for (; count >= 8; c += 8, count -= 8) { | ||
| uint64_t x = *reinterpret_cast<const uint64_t *>(c); | ||
| if (x != 0) { | ||
| return res + ClzllWithEndian(x); | ||
| } | ||
| res += 64; | ||
| } | ||
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| if (count > 0) { | ||
| uint64_t v = 0; | ||
| __builtin_memcpy(&v, c, count); | ||
| res += v == 0 ? count * 8 : ClzllWithEndian(v); | ||
| } | ||
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| if (res == ct * 8) { | ||
| return -1; | ||
| } | ||
| } else { | ||
| for (; count >= 8; c += 8, count -= 8) { | ||
| uint64_t x = *reinterpret_cast<const uint64_t *>(c); | ||
| if (x != (uint64_t)-1) { | ||
| return res + ClzllWithEndian(~x); | ||
| } | ||
| res += 64; | ||
| } | ||
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| if (count > 0) { | ||
| uint64_t v = -1; | ||
| __builtin_memcpy(&v, c, count); | ||
| res += v == (uint64_t)-1 ? count * 8 : ClzllWithEndian(~v); | ||
| } | ||
| } | ||
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| return res; | ||
| } | ||
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| } // namespace msb | ||
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| } // namespace util |
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