08552b19d3
Summary: A generic algorithm in progress depends on a templatized version of fastrange, so this change generalizes it and renames it to fit our style guidelines, FastRange32, FastRange64, and now FastRangeGeneric. Pull Request resolved: https://github.com/facebook/rocksdb/pull/7436 Test Plan: added a few more test cases Reviewed By: jay-zhuang Differential Revision: D23958153 Pulled By: pdillinger fbshipit-source-id: 8c3b76101653417804997e5f076623a25586f3e8
129 lines
4.6 KiB
C++
129 lines
4.6 KiB
C++
// Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
|
|
// This source code is licensed under both the GPLv2 (found in the
|
|
// COPYING file in the root directory) and Apache 2.0 License
|
|
// (found in the LICENSE.Apache file in the root directory).
|
|
|
|
#pragma once
|
|
|
|
#include <assert.h>
|
|
#ifdef _MSC_VER
|
|
#include <intrin.h>
|
|
#endif
|
|
|
|
#include <cstdint>
|
|
#include <type_traits>
|
|
|
|
namespace ROCKSDB_NAMESPACE {
|
|
|
|
// Fast implementation of floor(log2(v)). Undefined for 0 or negative
|
|
// numbers (in case of signed type).
|
|
template <typename T>
|
|
inline int FloorLog2(T v) {
|
|
static_assert(std::is_integral<T>::value, "non-integral type");
|
|
assert(v > 0);
|
|
#ifdef _MSC_VER
|
|
static_assert(sizeof(T) <= sizeof(uint64_t), "type too big");
|
|
unsigned long lz = 0;
|
|
if (sizeof(T) <= sizeof(uint32_t)) {
|
|
_BitScanReverse(&lz, static_cast<uint32_t>(v));
|
|
} else {
|
|
_BitScanReverse64(&lz, static_cast<uint64_t>(v));
|
|
}
|
|
return 63 - static_cast<int>(lz);
|
|
#else
|
|
static_assert(sizeof(T) <= sizeof(unsigned long long), "type too big");
|
|
if (sizeof(T) <= sizeof(unsigned int)) {
|
|
int lz = __builtin_clz(static_cast<unsigned int>(v));
|
|
return int{sizeof(unsigned int)} * 8 - 1 - lz;
|
|
} else if (sizeof(T) <= sizeof(unsigned long)) {
|
|
int lz = __builtin_clzl(static_cast<unsigned long>(v));
|
|
return int{sizeof(unsigned long)} * 8 - 1 - lz;
|
|
} else {
|
|
int lz = __builtin_clzll(static_cast<unsigned long long>(v));
|
|
return int{sizeof(unsigned long long)} * 8 - 1 - lz;
|
|
}
|
|
#endif
|
|
}
|
|
|
|
// Number of low-order zero bits before the first 1 bit. Undefined for 0.
|
|
template <typename T>
|
|
inline int CountTrailingZeroBits(T v) {
|
|
static_assert(std::is_integral<T>::value, "non-integral type");
|
|
assert(v != 0);
|
|
#ifdef _MSC_VER
|
|
static_assert(sizeof(T) <= sizeof(uint64_t), "type too big");
|
|
unsigned long tz = 0;
|
|
if (sizeof(T) <= sizeof(uint32_t)) {
|
|
_BitScanForward(&tz, static_cast<uint32_t>(v));
|
|
} else {
|
|
_BitScanForward64(&tz, static_cast<uint64_t>(v));
|
|
}
|
|
return static_cast<int>(tz);
|
|
#else
|
|
static_assert(sizeof(T) <= sizeof(unsigned long long), "type too big");
|
|
if (sizeof(T) <= sizeof(unsigned int)) {
|
|
return __builtin_ctz(static_cast<unsigned int>(v));
|
|
} else if (sizeof(T) <= sizeof(unsigned long)) {
|
|
return __builtin_ctzl(static_cast<unsigned long>(v));
|
|
} else {
|
|
return __builtin_ctzll(static_cast<unsigned long long>(v));
|
|
}
|
|
#endif
|
|
}
|
|
|
|
// Number of bits set to 1. Also known as "population count".
|
|
template <typename T>
|
|
inline int BitsSetToOne(T v) {
|
|
static_assert(std::is_integral<T>::value, "non-integral type");
|
|
#ifdef _MSC_VER
|
|
static_assert(sizeof(T) <= sizeof(uint64_t), "type too big");
|
|
if (sizeof(T) < sizeof(uint32_t)) {
|
|
// This bit mask is to avoid a compiler warning on unused path
|
|
constexpr auto mm = 8 * sizeof(uint32_t) - 1;
|
|
// The bit mask is to neutralize sign extension on small signed types
|
|
constexpr uint32_t m = (uint32_t{1} << ((8 * sizeof(T)) & mm)) - 1;
|
|
return static_cast<int>(__popcnt(static_cast<uint32_t>(v) & m));
|
|
} else if (sizeof(T) == sizeof(uint32_t)) {
|
|
return static_cast<int>(__popcnt(static_cast<uint32_t>(v)));
|
|
} else {
|
|
return static_cast<int>(__popcnt64(static_cast<uint64_t>(v)));
|
|
}
|
|
#else
|
|
static_assert(sizeof(T) <= sizeof(unsigned long long), "type too big");
|
|
if (sizeof(T) < sizeof(unsigned int)) {
|
|
// This bit mask is to avoid a compiler warning on unused path
|
|
constexpr auto mm = 8 * sizeof(unsigned int) - 1;
|
|
// This bit mask is to neutralize sign extension on small signed types
|
|
constexpr unsigned int m = (1U << ((8 * sizeof(T)) & mm)) - 1;
|
|
return __builtin_popcount(static_cast<unsigned int>(v) & m);
|
|
} else if (sizeof(T) == sizeof(unsigned int)) {
|
|
return __builtin_popcount(static_cast<unsigned int>(v));
|
|
} else if (sizeof(T) <= sizeof(unsigned long)) {
|
|
return __builtin_popcountl(static_cast<unsigned long>(v));
|
|
} else {
|
|
return __builtin_popcountll(static_cast<unsigned long long>(v));
|
|
}
|
|
#endif
|
|
}
|
|
|
|
template <typename T>
|
|
inline int BitParity(T v) {
|
|
static_assert(std::is_integral<T>::value, "non-integral type");
|
|
#ifdef _MSC_VER
|
|
// bit parity == oddness of popcount
|
|
return BitsSetToOne(v) & 1;
|
|
#else
|
|
static_assert(sizeof(T) <= sizeof(unsigned long long), "type too big");
|
|
if (sizeof(T) <= sizeof(unsigned int)) {
|
|
// On any sane systen, potential sign extension here won't change parity
|
|
return __builtin_parity(static_cast<unsigned int>(v));
|
|
} else if (sizeof(T) <= sizeof(unsigned long)) {
|
|
return __builtin_parityl(static_cast<unsigned long>(v));
|
|
} else {
|
|
return __builtin_parityll(static_cast<unsigned long long>(v));
|
|
}
|
|
#endif
|
|
}
|
|
|
|
} // namespace ROCKSDB_NAMESPACE
|