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