chromium/third_party/spirv-tools/src/source/util/bitutils.h

// Copyright (c) 2015-2016 The Khronos Group Inc.
//
// 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
//
//     http://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.

#ifndef SOURCE_UTIL_BITUTILS_H_
#define SOURCE_UTIL_BITUTILS_H_

#include <cassert>
#include <cstdint>
#include <cstring>
#include <type_traits>

namespace spvtools {
namespace utils {

// Performs a bitwise copy of source to the destination type Dest.
template <typename Dest, typename Src>
Dest BitwiseCast(Src source) { … }

// Calculates the bit width of the integer type |T|.
template <typename T>
struct IntegerBitWidth { … };

// SetBits<T, First, Num> returns an integer of type <T> with bits set
// for position <First> through <First + Num - 1>, counting from the least
// significant bit. In particular when Num == 0, no positions are set to 1.
// A static assert will be triggered if First + Num > sizeof(T) * 8, that is,
// a bit that will not fit in the underlying type is set.
template <typename T, size_t First = 0, size_t Num = 0>
struct SetBits { … };

SetBits<T, Last, 0>;

// This is all compile-time so we can put our tests right here.
static_assert …;
static_assert …;
static_assert …;
static_assert …;

static_assert …;
static_assert …;
static_assert …;
static_assert …;
static_assert …;
static_assert …;
static_assert …;
static_assert …;

static_assert …;
static_assert …;
static_assert …;
static_assert …;
static_assert …;

// Returns number of '1' bits in a word.
template <typename T>
size_t CountSetBits(T word) { … }

// Checks if the bit at the |position| is set to '1'.
// Bits zero-indexed starting at the least significant bit.
// |position| must be within the bit width of |T|.
template <typename T>
bool IsBitAtPositionSet(T word, size_t position) { … }

// Returns a value obtained by setting a range of adjacent bits of |word| to
// |value|. Affected bits are within the range:
//   [first_position, first_position + num_bits_to_mutate),
// assuming zero-based indexing starting at the least
// significant bit. Bits to mutate must be within the bit width of |T|.
template <typename T>
T MutateBits(T word, size_t first_position, size_t num_bits_to_mutate,
             bool value) { … }

// Returns a value obtained by setting the |num_bits_to_set| highest bits to
// '1'. |num_bits_to_set| must be not be greater than the bit width of |T|.
template <typename T>
T SetHighBits(T word, size_t num_bits_to_set) { … }

// Returns a value obtained by setting the |num_bits_to_set| highest bits to
// '0'. |num_bits_to_set| must be not be greater than the bit width of |T|.
template <typename T>
T ClearHighBits(T word, size_t num_bits_to_set) { … }

// Returns the value obtained by extracting the |number_of_bits| least
// significant bits from |value|, and sign-extending it to 64-bits.
template <typename T>
T SignExtendValue(T value, uint32_t number_of_bits) { … }

// Returns the value obtained by extracting the |number_of_bits| least
// significant bits from |value|, and zero-extending it to 64-bits.
template <typename T>
T ZeroExtendValue(T value, uint32_t number_of_bits) { … }

}  // namespace utils
}  // namespace spvtools

#endif  // SOURCE_UTIL_BITUTILS_H_