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LibCrypto: Add BigFraction

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This new abstraction allows the user to store rational numbers with
infinite precision.
This commit is contained in:
Lucas CHOLLET 2022-01-16 12:28:51 +01:00 • committed by Sam Atkins
parent 62b8ccaffc
commit 6a937312b3
3 changed files with 326 additions and 0 deletions
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74
Userland/Libraries/LibCrypto/BigFraction/BigFraction.h Normal file
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/*
* Copyright (c) 2022, Lucas Chollet <lucas.chollet@free.fr>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/String.h>
#include <LibCrypto/BigInt/SignedBigInteger.h>
namespace Crypto {
class BigFraction {
// FIXME Make the whole API more error-friendly. This includes:
// - Propagating errors from BigIntegers
// - Returns errors from both BigFraction(StringView) and BigFraction(numerator, denominator);
// - Duplicate fallible operators with a error-friendly version
public:
BigFraction() = default;
explicit BigFraction(Crypto::SignedBigInteger);
BigFraction(Crypto::SignedBigInteger numerator, Crypto::UnsignedBigInteger denominator);
BigFraction(Crypto::BigFraction const&) = default;
BigFraction(Crypto::BigFraction&&) = default;
BigFraction& operator=(Crypto::BigFraction const&) = default;
BigFraction& operator=(Crypto::BigFraction&&) = default;
explicit BigFraction(StringView);
explicit BigFraction(double);
BigFraction operator+(BigFraction const&) const;
BigFraction operator-(BigFraction const&) const;
BigFraction operator*(BigFraction const&) const;
BigFraction operator/(BigFraction const&) const;
BigFraction operator-() const;
bool operator<(BigFraction const&) const;
bool operator==(BigFraction const&) const;
BigFraction invert() const;
BigFraction sqrt() const;
void set_to_0();
// Return a BigFraction in "scientific notation", as an example with:
// - m_numerator = 2
// - m_denominator = 3
// - rounding_threshold = 4
// The returned BigFraction will have:
// - m_numerator = 6667
// - m_denominator = 10000
BigFraction rounded(unsigned rounding_threshold) const;
String to_string(unsigned rounding_threshold) const;
double to_double() const;
private:
void reduce();
// This class uses a pair of integers to store a value. The purpose is to
// support any rational number without any numerical errors.
// For example, if we were to represent the value -123.55 in this format,
// the values could be -12355 for and 100 for m_denominator. However, this
// pair of value is not unique and the value will be reduced to -2471/20.
// This way, most operations don't have to be performed on doubles, but can
// be performed without loss of precision on this class.
Crypto::SignedBigInteger m_numerator { 0 };
Crypto::UnsignedBigInteger m_denominator { 1 };
};
}