| // Copyright 2019 Google LLC |
| // |
| // 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 |
| // |
| // https://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. |
| |
| // This file contains various utility routines for manipulating values at a low |
| // level, such as byte swaps and safe casts. |
| #ifndef EMBOSS_PUBLIC_EMBOSS_BIT_UTIL_H_ |
| #define EMBOSS_PUBLIC_EMBOSS_BIT_UTIL_H_ |
| |
| #include <cstdint> |
| #include <type_traits> |
| |
| #include "runtime/cpp/emboss_defines.h" |
| |
| namespace emboss { |
| namespace support { |
| |
| // Where possible, it is best to use byte swap builtins, but if they are not |
| // available ByteSwap can fall back to portable code. |
| inline constexpr ::std::uint8_t ByteSwap(::std::uint8_t x) { return x; } |
| inline constexpr ::std::uint16_t ByteSwap(::std::uint16_t x) { |
| #ifdef EMBOSS_BYTESWAP16 |
| return EMBOSS_BYTESWAP16(x); |
| #else |
| return (x << 8) | (x >> 8); |
| #endif |
| } |
| inline constexpr ::std::uint32_t ByteSwap(::std::uint32_t x) { |
| #ifdef EMBOSS_BYTESWAP32 |
| return EMBOSS_BYTESWAP32(x); |
| #else |
| return (static_cast</**/ ::std::uint32_t>( |
| ByteSwap(static_cast</**/ ::std::uint16_t>(x))) |
| << 16) | |
| ByteSwap(static_cast</**/ ::std::uint16_t>(x >> 16)); |
| #endif |
| } |
| inline constexpr ::std::uint64_t ByteSwap(::std::uint64_t x) { |
| #ifdef EMBOSS_BYTESWAP64 |
| return EMBOSS_BYTESWAP64(x); |
| #else |
| return (static_cast</**/ ::std::uint64_t>( |
| ByteSwap(static_cast</**/ ::std::uint32_t>(x))) |
| << 32) | |
| ByteSwap(static_cast</**/ ::std::uint32_t>(x >> 32)); |
| #endif |
| } |
| |
| // Masks the given value to the given number of bits. |
| template <typename T> |
| inline constexpr T MaskToNBits(T value, unsigned bits) { |
| static_assert(!::std::is_signed<T>::value, |
| "MaskToNBits only works on unsigned values."); |
| return bits < sizeof value * 8 ? value & ((static_cast<T>(1) << bits) - 1) |
| : value; |
| } |
| |
| template <typename T> |
| inline constexpr bool IsPowerOfTwo(T value) { |
| // This check relies on an old bit-counting trick; x & (x - 1) always has one |
| // fewer bit set to 1 than x (if x is nonzero), and powers of 2 always have |
| // exactly one 1 bit, thus x & (x - 1) == 0 if x is a power of 2. |
| return value > 0 && (value & (value - 1)) == 0; |
| } |
| |
| } // namespace support |
| } // namespace emboss |
| |
| #endif // EMBOSS_PUBLIC_EMBOSS_BIT_UTIL_H_ |