85 lines
2.9 KiB
C++
85 lines
2.9 KiB
C++
/*
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* Copyright 2021 The Android Open Source Project
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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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*/
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#pragma once
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#include <limits>
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#include <type_traits>
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#include <ftl/details/cast.h>
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namespace android::ftl {
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enum class CastSafety { kSafe, kUnderflow, kOverflow };
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// Returns whether static_cast<R>(v) is safe, or would result in underflow or overflow.
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//
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// static_assert(ftl::cast_safety<uint8_t>(-1) == ftl::CastSafety::kUnderflow);
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// static_assert(ftl::cast_safety<int8_t>(128u) == ftl::CastSafety::kOverflow);
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//
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// static_assert(ftl::cast_safety<uint32_t>(-.1f) == ftl::CastSafety::kUnderflow);
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// static_assert(ftl::cast_safety<int32_t>(static_cast<float>(INT32_MAX)) ==
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// ftl::CastSafety::kOverflow);
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//
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// static_assert(ftl::cast_safety<float>(-DBL_MAX) == ftl::CastSafety::kUnderflow);
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//
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template <typename R, typename T>
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constexpr CastSafety cast_safety(T v) {
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static_assert(std::is_arithmetic_v<T>);
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static_assert(std::is_arithmetic_v<R>);
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constexpr bool kFromSigned = std::is_signed_v<T>;
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constexpr bool kToSigned = std::is_signed_v<R>;
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using details::max_exponent;
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// If the R range contains the T range, then casting is always safe.
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if constexpr ((kFromSigned == kToSigned && max_exponent<R> >= max_exponent<T>) ||
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(!kFromSigned && kToSigned && max_exponent<R> > max_exponent<T>)) {
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return CastSafety::kSafe;
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}
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using C = std::common_type_t<R, T>;
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if constexpr (kFromSigned) {
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using L = details::safe_limits<R, T>;
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if constexpr (kToSigned) {
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// Signed to signed.
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if (v < L::lowest()) return CastSafety::kUnderflow;
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return v <= L::max() ? CastSafety::kSafe : CastSafety::kOverflow;
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} else {
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// Signed to unsigned.
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if (v < 0) return CastSafety::kUnderflow;
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return static_cast<C>(v) <= static_cast<C>(L::max()) ? CastSafety::kSafe
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: CastSafety::kOverflow;
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}
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} else {
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using L = std::numeric_limits<R>;
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if constexpr (kToSigned) {
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// Unsigned to signed.
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return static_cast<C>(v) <= static_cast<C>(L::max()) ? CastSafety::kSafe
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: CastSafety::kOverflow;
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} else {
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// Unsigned to unsigned.
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return v <= L::max() ? CastSafety::kSafe : CastSafety::kOverflow;
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}
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}
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}
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} // namespace android::ftl
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