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188 lines
7.1 KiB
188 lines
7.1 KiB
// Copyright (c) 2015-2016 The Khronos Group Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef SOURCE_UTIL_BITUTILS_H_
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#define SOURCE_UTIL_BITUTILS_H_
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#include <cassert>
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#include <cstdint>
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#include <cstring>
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#include <type_traits>
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namespace spvtools {
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namespace utils {
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// Performs a bitwise copy of source to the destination type Dest.
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template <typename Dest, typename Src>
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Dest BitwiseCast(Src source) {
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Dest dest;
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static_assert(sizeof(source) == sizeof(dest),
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"BitwiseCast: Source and destination must have the same size");
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std::memcpy(&dest, &source, sizeof(dest));
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return dest;
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}
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// Calculates the bit width of the integer type |T|.
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template <typename T>
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struct IntegerBitWidth {
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static_assert(std::is_integral<T>::value, "Integer type required");
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static const size_t kBitsPerByte = 8;
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static const size_t get = sizeof(T) * kBitsPerByte;
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};
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// SetBits<T, First, Num> returns an integer of type <T> with bits set
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// for position <First> through <First + Num - 1>, counting from the least
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// significant bit. In particular when Num == 0, no positions are set to 1.
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// A static assert will be triggered if First + Num > sizeof(T) * 8, that is,
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// a bit that will not fit in the underlying type is set.
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template <typename T, size_t First = 0, size_t Num = 0>
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struct SetBits {
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static_assert(First < IntegerBitWidth<T>::get,
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"Tried to set a bit that is shifted too far.");
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const static T get = (T(1) << First) | SetBits<T, First + 1, Num - 1>::get;
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};
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template <typename T, size_t Last>
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struct SetBits<T, Last, 0> {
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const static T get = T(0);
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};
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// This is all compile-time so we can put our tests right here.
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static_assert(IntegerBitWidth<uint32_t>::get == 32, "IntegerBitWidth mismatch");
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static_assert(IntegerBitWidth<int32_t>::get == 32, "IntegerBitWidth mismatch");
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static_assert(IntegerBitWidth<uint64_t>::get == 64, "IntegerBitWidth mismatch");
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static_assert(IntegerBitWidth<uint8_t>::get == 8, "IntegerBitWidth mismatch");
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static_assert(SetBits<uint32_t, 0, 0>::get == uint32_t(0x00000000),
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"SetBits failed");
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static_assert(SetBits<uint32_t, 0, 1>::get == uint32_t(0x00000001),
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"SetBits failed");
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static_assert(SetBits<uint32_t, 31, 1>::get == uint32_t(0x80000000),
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"SetBits failed");
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static_assert(SetBits<uint32_t, 1, 2>::get == uint32_t(0x00000006),
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"SetBits failed");
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static_assert(SetBits<uint32_t, 30, 2>::get == uint32_t(0xc0000000),
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"SetBits failed");
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static_assert(SetBits<uint32_t, 0, 31>::get == uint32_t(0x7FFFFFFF),
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"SetBits failed");
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static_assert(SetBits<uint32_t, 0, 32>::get == uint32_t(0xFFFFFFFF),
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"SetBits failed");
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static_assert(SetBits<uint32_t, 16, 16>::get == uint32_t(0xFFFF0000),
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"SetBits failed");
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static_assert(SetBits<uint64_t, 0, 1>::get == uint64_t(0x0000000000000001LL),
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"SetBits failed");
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static_assert(SetBits<uint64_t, 63, 1>::get == uint64_t(0x8000000000000000LL),
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"SetBits failed");
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static_assert(SetBits<uint64_t, 62, 2>::get == uint64_t(0xc000000000000000LL),
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"SetBits failed");
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static_assert(SetBits<uint64_t, 31, 1>::get == uint64_t(0x0000000080000000LL),
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"SetBits failed");
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static_assert(SetBits<uint64_t, 16, 16>::get == uint64_t(0x00000000FFFF0000LL),
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"SetBits failed");
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// Returns number of '1' bits in a word.
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template <typename T>
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size_t CountSetBits(T word) {
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static_assert(std::is_integral<T>::value,
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"CountSetBits requires integer type");
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size_t count = 0;
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while (word) {
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word &= word - 1;
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++count;
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}
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return count;
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}
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// Checks if the bit at the |position| is set to '1'.
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// Bits zero-indexed starting at the least significant bit.
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// |position| must be within the bit width of |T|.
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template <typename T>
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bool IsBitAtPositionSet(T word, size_t position) {
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static_assert(std::is_integral<T>::value, "Integer type required");
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static_assert(std::is_unsigned<T>::value, "Unsigned type required");
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assert(position < IntegerBitWidth<T>::get &&
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"position must be less than the bit width");
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return word & T(T(1) << position);
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}
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// Returns a value obtained by setting a range of adjacent bits of |word| to
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// |value|. Affected bits are within the range:
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// [first_position, first_position + num_bits_to_mutate),
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// assuming zero-based indexing starting at the least
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// significant bit. Bits to mutate must be within the bit width of |T|.
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template <typename T>
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T MutateBits(T word, size_t first_position, size_t num_bits_to_mutate,
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bool value) {
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static_assert(std::is_integral<T>::value, "Integer type required");
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static_assert(std::is_unsigned<T>::value, "Unsigned type required");
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static const size_t word_bit_width = IntegerBitWidth<T>::get;
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assert(first_position < word_bit_width &&
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"Mutated bits must be within bit width");
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assert(first_position + num_bits_to_mutate <= word_bit_width &&
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"Mutated bits must be within bit width");
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if (num_bits_to_mutate == 0) {
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return word;
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}
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const T all_ones = ~T(0);
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const size_t num_unaffected_low_bits = first_position;
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const T unaffected_low_mask =
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T(T(all_ones >> num_unaffected_low_bits) << num_unaffected_low_bits);
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const size_t num_unaffected_high_bits =
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word_bit_width - (first_position + num_bits_to_mutate);
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const T unaffected_high_mask =
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T(T(all_ones << num_unaffected_high_bits) >> num_unaffected_high_bits);
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const T mutation_mask = unaffected_low_mask & unaffected_high_mask;
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if (value) {
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return word | mutation_mask;
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}
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return word & T(~mutation_mask);
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}
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// Returns a value obtained by setting the |num_bits_to_set| highest bits to
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// '1'. |num_bits_to_set| must be not be greater than the bit width of |T|.
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template <typename T>
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T SetHighBits(T word, size_t num_bits_to_set) {
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if (num_bits_to_set == 0) {
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return word;
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}
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const size_t word_bit_width = IntegerBitWidth<T>::get;
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assert(num_bits_to_set <= word_bit_width &&
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"Can't set more bits than bit width");
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return MutateBits(word, word_bit_width - num_bits_to_set, num_bits_to_set,
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true);
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}
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// Returns a value obtained by setting the |num_bits_to_set| highest bits to
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// '0'. |num_bits_to_set| must be not be greater than the bit width of |T|.
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template <typename T>
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T ClearHighBits(T word, size_t num_bits_to_set) {
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if (num_bits_to_set == 0) {
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return word;
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}
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const size_t word_bit_width = IntegerBitWidth<T>::get;
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assert(num_bits_to_set <= word_bit_width &&
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"Can't clear more bits than bit width");
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return MutateBits(word, word_bit_width - num_bits_to_set, num_bits_to_set,
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false);
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}
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} // namespace utils
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} // namespace spvtools
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#endif // SOURCE_UTIL_BITUTILS_H_
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