150 lines
3.9 KiB
C++
150 lines
3.9 KiB
C++
// Copyright 2017 The Abseil Authors.
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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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// https://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 ABSL_RANDOM_INTERNAL_TRAITS_H_
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#define ABSL_RANDOM_INTERNAL_TRAITS_H_
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#include <cstdint>
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#include <limits>
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#include <type_traits>
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#include "absl/base/config.h"
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#include "absl/numeric/bits.h"
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#include "absl/numeric/int128.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace random_internal {
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// random_internal::is_widening_convertible<A, B>
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//
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// Returns whether a type A is widening-convertible to a type B.
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//
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// A is widening-convertible to B means:
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// A a = <any number>;
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// B b = a;
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// A c = b;
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// EXPECT_EQ(a, c);
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template <typename A, typename B>
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class is_widening_convertible {
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// As long as there are enough bits in the exact part of a number:
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// - unsigned can fit in float, signed, unsigned
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// - signed can fit in float, signed
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// - float can fit in float
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// So we define rank to be:
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// - rank(float) -> 2
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// - rank(signed) -> 1
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// - rank(unsigned) -> 0
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template <class T>
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static constexpr int rank() {
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return !std::numeric_limits<T>::is_integer +
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std::numeric_limits<T>::is_signed;
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}
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public:
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// If an arithmetic-type B can represent at least as many digits as a type A,
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// and B belongs to a rank no lower than A, then A can be safely represented
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// by B through a widening-conversion.
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static constexpr bool value =
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std::numeric_limits<A>::digits <= std::numeric_limits<B>::digits &&
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rank<A>() <= rank<B>();
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};
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template <typename T>
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struct IsIntegral : std::is_integral<T> {};
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template <>
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struct IsIntegral<absl::int128> : std::true_type {};
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template <>
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struct IsIntegral<absl::uint128> : std::true_type {};
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template <typename T>
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struct MakeUnsigned : std::make_unsigned<T> {};
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template <>
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struct MakeUnsigned<absl::int128> {
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using type = absl::uint128;
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};
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template <>
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struct MakeUnsigned<absl::uint128> {
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using type = absl::uint128;
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};
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template <typename T>
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struct IsUnsigned : std::is_unsigned<T> {};
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template <>
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struct IsUnsigned<absl::int128> : std::false_type {};
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template <>
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struct IsUnsigned<absl::uint128> : std::true_type {};
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// unsigned_bits<N>::type returns the unsigned int type with the indicated
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// number of bits.
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template <size_t N>
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struct unsigned_bits;
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template <>
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struct unsigned_bits<8> {
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using type = uint8_t;
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};
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template <>
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struct unsigned_bits<16> {
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using type = uint16_t;
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};
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template <>
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struct unsigned_bits<32> {
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using type = uint32_t;
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};
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template <>
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struct unsigned_bits<64> {
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using type = uint64_t;
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};
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template <>
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struct unsigned_bits<128> {
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using type = absl::uint128;
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};
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// 256-bit wrapper for wide multiplications.
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struct U256 {
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uint128 hi;
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uint128 lo;
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};
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template <>
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struct unsigned_bits<256> {
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using type = U256;
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};
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template <typename IntType>
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struct make_unsigned_bits {
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using type = typename unsigned_bits<
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std::numeric_limits<typename MakeUnsigned<IntType>::type>::digits>::type;
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};
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template <typename T>
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int BitWidth(T v) {
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// Workaround for bit_width not supporting int128.
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// Don't hardcode `64` to make sure this code does not trigger compiler
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// warnings in smaller types.
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constexpr int half_bits = sizeof(T) * 8 / 2;
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if (sizeof(T) == 16 && (v >> half_bits) != 0) {
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return bit_width(static_cast<uint64_t>(v >> half_bits)) + half_bits;
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} else {
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return bit_width(static_cast<uint64_t>(v));
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}
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}
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} // namespace random_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_RANDOM_INTERNAL_TRAITS_H_
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