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df82adca43
This one verifies bitmasks where low bits are set to 1 (hence the name). Any stray 0 among the lower ones or any stray 1 among the higher zeros renders the mask invalid. The edge cases of all zeros and all ones are considered valid masks. It uses an efficient implementation. It's the counterpart of https://graphics.stanford.edu/~seander/bithacks.html#DetermineIfPowerOf2
124 lines
3.7 KiB
C++
124 lines
3.7 KiB
C++
// Copyright 2017 Dolphin Emulator Project
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// Licensed under GPLv2+
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// Refer to the license.txt file included.
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#pragma once
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#include <climits>
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#include <cstddef>
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#include <type_traits>
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namespace Common
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{
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///
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/// Retrieves the size of a type in bits.
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///
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/// @tparam T Type to get the size of.
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///
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/// @return the size of the type in bits.
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///
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template <typename T>
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constexpr size_t BitSize() noexcept
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{
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return sizeof(T) * CHAR_BIT;
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}
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///
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/// Extracts a bit from a value.
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///
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/// @param src The value to extract a bit from.
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/// @param bit The bit to extract.
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///
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/// @tparam T The type of the value.
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///
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/// @return The extracted bit.
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///
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template <typename T>
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constexpr T ExtractBit(const T src, const size_t bit) noexcept
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{
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return (src >> bit) & static_cast<T>(1);
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}
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///
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/// Extracts a bit from a value.
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///
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/// @param src The value to extract a bit from.
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///
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/// @tparam bit The bit to extract.
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/// @tparam T The type of the value.
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///
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/// @return The extracted bit.
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///
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template <size_t bit, typename T>
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constexpr T ExtractBit(const T src) noexcept
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{
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static_assert(bit < BitSize<T>(), "Specified bit must be within T's bit width.");
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return ExtractBit(src, bit);
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}
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///
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/// Extracts a range of bits from a value.
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///
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/// @param src The value to extract the bits from.
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/// @param begin The beginning of the bit range. This is inclusive.
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/// @param end The ending of the bit range. This is inclusive.
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///
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/// @tparam T The type of the value.
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/// @tparam Result The returned result type. This is the unsigned analog
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/// of a signed type if a signed type is passed as T.
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///
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/// @return The extracted bits.
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///
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template <typename T, typename Result = std::make_unsigned_t<T>>
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constexpr Result ExtractBits(const T src, const size_t begin, const size_t end) noexcept
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{
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return static_cast<Result>(((static_cast<Result>(src) << ((BitSize<T>() - 1) - end)) >>
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(BitSize<T>() - end + begin - 1)));
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}
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///
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/// Extracts a range of bits from a value.
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///
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/// @param src The value to extract the bits from.
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///
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/// @tparam begin The beginning of the bit range. This is inclusive.
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/// @tparam end The ending of the bit range. This is inclusive.
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/// @tparam T The type of the value.
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/// @tparam Result The returned result type. This is the unsigned analog
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/// of a signed type if a signed type is passed as T.
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///
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/// @return The extracted bits.
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///
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template <size_t begin, size_t end, typename T, typename Result = std::make_unsigned_t<T>>
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constexpr Result ExtractBits(const T src) noexcept
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{
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static_assert(begin < end, "Beginning bit must be less than the ending bit.");
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static_assert(begin < BitSize<T>(), "Beginning bit is larger than T's bit width.");
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static_assert(end < BitSize<T>(), "Ending bit is larger than T's bit width.");
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return ExtractBits<T, Result>(src, begin, end);
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}
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///
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/// Verifies whether the supplied value is a valid bit mask of the form 0b00...0011...11.
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/// Both edge cases of all zeros and all ones are considered valid masks, too.
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///
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/// @param mask The mask value to test for validity.
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///
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/// @tparam T The type of the value.
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///
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/// @return A bool indicating whether the mask is valid.
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///
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template <typename T>
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constexpr bool IsValidLowMask(const T mask) noexcept
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{
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static_assert(std::is_integral<T>::value, "Mask must be an integral type.");
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static_assert(std::is_unsigned<T>::value, "Signed masks can introduce hard to find bugs.");
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// Can be efficiently determined without looping or bit counting. It's the counterpart
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// to https://graphics.stanford.edu/~seander/bithacks.html#DetermineIfPowerOf2
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// and doesn't require special casing either edge case.
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return (mask & (mask + 1)) == 0;
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}
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} // namespace Common
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