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c03a2795a8
The helpers are used in the following commits to increase the safety of conversions during cache size calculations. Co-authored-by: Ryan Ofsky <ryan@ofsky.org> Co-authored-by: stickies-v <stickies-v@protonmail.com>
87 lines
2.9 KiB
C++
87 lines
2.9 KiB
C++
// Copyright (c) 2021-2022 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#ifndef BITCOIN_UTIL_OVERFLOW_H
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#define BITCOIN_UTIL_OVERFLOW_H
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#include <climits>
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#include <concepts>
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#include <limits>
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#include <optional>
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#include <type_traits>
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template <class T>
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[[nodiscard]] bool AdditionOverflow(const T i, const T j) noexcept
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{
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static_assert(std::is_integral<T>::value, "Integral required.");
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if constexpr (std::numeric_limits<T>::is_signed) {
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return (i > 0 && j > std::numeric_limits<T>::max() - i) ||
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(i < 0 && j < std::numeric_limits<T>::min() - i);
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}
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return std::numeric_limits<T>::max() - i < j;
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}
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template <class T>
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[[nodiscard]] std::optional<T> CheckedAdd(const T i, const T j) noexcept
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{
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if (AdditionOverflow(i, j)) {
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return std::nullopt;
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}
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return i + j;
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}
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template <class T>
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[[nodiscard]] T SaturatingAdd(const T i, const T j) noexcept
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{
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if constexpr (std::numeric_limits<T>::is_signed) {
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if (i > 0 && j > std::numeric_limits<T>::max() - i) {
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return std::numeric_limits<T>::max();
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}
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if (i < 0 && j < std::numeric_limits<T>::min() - i) {
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return std::numeric_limits<T>::min();
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}
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} else {
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if (std::numeric_limits<T>::max() - i < j) {
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return std::numeric_limits<T>::max();
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}
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}
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return i + j;
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}
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/**
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* @brief Left bit shift with overflow checking.
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* @param input The input value to be left shifted.
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* @param shift The number of bits to left shift.
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* @return (input * 2^shift) or nullopt if it would not fit in the return type.
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*/
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template <std::integral T>
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constexpr std::optional<T> CheckedLeftShift(T input, unsigned shift) noexcept
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{
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if (shift == 0 || input == 0) return input;
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// Avoid undefined c++ behaviour if shift is >= number of bits in T.
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if (shift >= sizeof(T) * CHAR_BIT) return std::nullopt;
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// If input << shift is too big to fit in T, return nullopt.
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if (input > (std::numeric_limits<T>::max() >> shift)) return std::nullopt;
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if (input < (std::numeric_limits<T>::min() >> shift)) return std::nullopt;
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return input << shift;
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}
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/**
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* @brief Left bit shift with safe minimum and maximum values.
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* @param input The input value to be left shifted.
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* @param shift The number of bits to left shift.
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* @return (input * 2^shift) clamped to fit between the lowest and highest
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* representable values of the type T.
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*/
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template <std::integral T>
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constexpr T SaturatingLeftShift(T input, unsigned shift) noexcept
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{
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if (auto result{CheckedLeftShift(input, shift)}) return *result;
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// If input << shift is too big to fit in T, return biggest positive or negative
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// number that fits.
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return input < 0 ? std::numeric_limits<T>::min() : std::numeric_limits<T>::max();
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}
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#endif // BITCOIN_UTIL_OVERFLOW_H
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