fork of https://github.com/oxigraph/rocksdb and https://github.com/facebook/rocksdb for nextgraph and oxigraph
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128 lines
4.6 KiB
128 lines
4.6 KiB
// Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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#pragma once
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#include <assert.h>
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#ifdef _MSC_VER
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#include <intrin.h>
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#endif
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#include <cstdint>
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#include <type_traits>
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namespace ROCKSDB_NAMESPACE {
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// Fast implementation of floor(log2(v)). Undefined for 0 or negative
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// numbers (in case of signed type).
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template <typename T>
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inline int FloorLog2(T v) {
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static_assert(std::is_integral<T>::value, "non-integral type");
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assert(v > 0);
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#ifdef _MSC_VER
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static_assert(sizeof(T) <= sizeof(uint64_t), "type too big");
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unsigned long lz = 0;
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if (sizeof(T) <= sizeof(uint32_t)) {
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_BitScanReverse(&lz, static_cast<uint32_t>(v));
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} else {
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_BitScanReverse64(&lz, static_cast<uint64_t>(v));
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}
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return 63 - static_cast<int>(lz);
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#else
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static_assert(sizeof(T) <= sizeof(unsigned long long), "type too big");
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if (sizeof(T) <= sizeof(unsigned int)) {
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int lz = __builtin_clz(static_cast<unsigned int>(v));
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return int{sizeof(unsigned int)} * 8 - 1 - lz;
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} else if (sizeof(T) <= sizeof(unsigned long)) {
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int lz = __builtin_clzl(static_cast<unsigned long>(v));
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return int{sizeof(unsigned long)} * 8 - 1 - lz;
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} else {
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int lz = __builtin_clzll(static_cast<unsigned long long>(v));
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return int{sizeof(unsigned long long)} * 8 - 1 - lz;
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}
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#endif
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}
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// Number of low-order zero bits before the first 1 bit. Undefined for 0.
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template <typename T>
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inline int CountTrailingZeroBits(T v) {
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static_assert(std::is_integral<T>::value, "non-integral type");
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assert(v != 0);
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#ifdef _MSC_VER
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static_assert(sizeof(T) <= sizeof(uint64_t), "type too big");
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unsigned long tz = 0;
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if (sizeof(T) <= sizeof(uint32_t)) {
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_BitScanForward(&tz, static_cast<uint32_t>(v));
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} else {
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_BitScanForward64(&tz, static_cast<uint64_t>(v));
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}
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return static_cast<int>(tz);
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#else
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static_assert(sizeof(T) <= sizeof(unsigned long long), "type too big");
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if (sizeof(T) <= sizeof(unsigned int)) {
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return __builtin_ctz(static_cast<unsigned int>(v));
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} else if (sizeof(T) <= sizeof(unsigned long)) {
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return __builtin_ctzl(static_cast<unsigned long>(v));
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} else {
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return __builtin_ctzll(static_cast<unsigned long long>(v));
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}
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#endif
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}
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// Number of bits set to 1. Also known as "population count".
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template <typename T>
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inline int BitsSetToOne(T v) {
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static_assert(std::is_integral<T>::value, "non-integral type");
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#ifdef _MSC_VER
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static_assert(sizeof(T) <= sizeof(uint64_t), "type too big");
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if (sizeof(T) < sizeof(uint32_t)) {
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// This bit mask is to avoid a compiler warning on unused path
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constexpr auto mm = 8 * sizeof(uint32_t) - 1;
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// The bit mask is to neutralize sign extension on small signed types
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constexpr uint32_t m = (uint32_t{1} << ((8 * sizeof(T)) & mm)) - 1;
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return static_cast<int>(__popcnt(static_cast<uint32_t>(v) & m));
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} else if (sizeof(T) == sizeof(uint32_t)) {
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return static_cast<int>(__popcnt(static_cast<uint32_t>(v)));
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} else {
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return static_cast<int>(__popcnt64(static_cast<uint64_t>(v)));
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}
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#else
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static_assert(sizeof(T) <= sizeof(unsigned long long), "type too big");
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if (sizeof(T) < sizeof(unsigned int)) {
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// This bit mask is to avoid a compiler warning on unused path
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constexpr auto mm = 8 * sizeof(unsigned int) - 1;
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// This bit mask is to neutralize sign extension on small signed types
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constexpr unsigned int m = (1U << ((8 * sizeof(T)) & mm)) - 1;
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return __builtin_popcount(static_cast<unsigned int>(v) & m);
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} else if (sizeof(T) == sizeof(unsigned int)) {
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return __builtin_popcount(static_cast<unsigned int>(v));
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} else if (sizeof(T) <= sizeof(unsigned long)) {
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return __builtin_popcountl(static_cast<unsigned long>(v));
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} else {
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return __builtin_popcountll(static_cast<unsigned long long>(v));
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}
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#endif
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}
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template <typename T>
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inline int BitParity(T v) {
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static_assert(std::is_integral<T>::value, "non-integral type");
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#ifdef _MSC_VER
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// bit parity == oddness of popcount
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return BitsSetToOne(v) & 1;
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#else
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static_assert(sizeof(T) <= sizeof(unsigned long long), "type too big");
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if (sizeof(T) <= sizeof(unsigned int)) {
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// On any sane systen, potential sign extension here won't change parity
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return __builtin_parity(static_cast<unsigned int>(v));
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} else if (sizeof(T) <= sizeof(unsigned long)) {
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return __builtin_parityl(static_cast<unsigned long>(v));
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} else {
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return __builtin_parityll(static_cast<unsigned long long>(v));
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}
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#endif
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}
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} // namespace ROCKSDB_NAMESPACE
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