ladybird/Libraries/LibCrypto/BigInt/SignedBigInteger.cpp

/*
 * Copyright (c) 2020, the SerenityOS developers.
 * All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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#include "SignedBigInteger.h"
#include <AK/StringBuilder.h>

namespace Crypto {

SignedBigInteger SignedBigInteger::import_data(const u8* ptr, size_t length)
{
    bool sign = *ptr;
    auto unsigned_data = UnsignedBigInteger::import_data(ptr + 1, length - 1);
    return { move(unsigned_data), sign };
}

size_t SignedBigInteger::export_data(AK::ByteBuffer& data) const
{
    data[0] = m_sign;
    auto bytes_view = data.slice_view(1, data.size() - 1);
    return m_unsigned_data.export_data(bytes_view) + 1;
}

SignedBigInteger SignedBigInteger::from_base10(StringView str)
{
    bool sign = false;
    if (str.length() > 1) {
        auto maybe_sign = str[0];
        if (maybe_sign == '-') {
            str = str.substring_view(1, str.length() - 1);
            sign = true;
        }
        if (maybe_sign == '+')
            str = str.substring_view(1, str.length() - 1);
    }
    auto unsigned_data = UnsignedBigInteger::from_base10(str);
    return { move(unsigned_data), sign };
}

String SignedBigInteger::to_base10() const
{
    StringBuilder builder;

    if (m_sign)
        builder.append('-');

    builder.append(m_unsigned_data.to_base10());

    return builder.to_string();
}

FLATTEN SignedBigInteger SignedBigInteger::plus(const SignedBigInteger& other) const
{
    // If both are of the same sign, just add the unsigned data and return.
    if (m_sign == other.m_sign)
        return { other.m_unsigned_data.plus(m_unsigned_data), m_sign };

    // One value is signed while the other is not.
    return m_sign ? other.minus(this->m_unsigned_data) : minus(other.m_unsigned_data);
}

FLATTEN SignedBigInteger SignedBigInteger::minus(const SignedBigInteger& other) const
{
    // If the signs are different, convert the op to an addition.
    if (m_sign != other.m_sign) {
        // -x - y = - (x + y)
        // x - -y = (x + y)
        SignedBigInteger result { other.m_unsigned_data.plus(this->m_unsigned_data) };
        if (m_sign)
            result.negate();
        return result;
    }

    if (!m_sign) {
        // Both operands are positive.
        // x - y = - (y - x)
        if (m_unsigned_data < other.m_unsigned_data) {
            // The result will be negative.
            return { other.m_unsigned_data.minus(m_unsigned_data), true };
        }

        // The result will be either zero, or positive.
        return SignedBigInteger { m_unsigned_data.minus(other.m_unsigned_data) };
    }

    // Both operands are negative.
    // -x - -y = y - x
    if (m_unsigned_data < other.m_unsigned_data) {
        // The result will be positive.
        return SignedBigInteger { m_unsigned_data.minus(other.m_unsigned_data) };
    }
    // The result will be either zero, or negative.
    // y - x = - (x - y)
    return { other.m_unsigned_data.minus(m_unsigned_data), true };
}

FLATTEN SignedBigInteger SignedBigInteger::plus(const UnsignedBigInteger& other) const
{
    if (m_sign) {
        if (other < m_unsigned_data)
            return { m_unsigned_data.minus(other), true };

        return { other.minus(m_unsigned_data), false };
    }

    return { m_unsigned_data.plus(other), false };
}

FLATTEN SignedBigInteger SignedBigInteger::minus(const UnsignedBigInteger& other) const
{
    if (m_sign)
        return { m_unsigned_data.plus(m_unsigned_data), true };

    if (other < m_unsigned_data)
        return { m_unsigned_data.minus(other), false };

    return { other.minus(m_unsigned_data), true };
}

bool SignedBigInteger::operator==(const UnsignedBigInteger& other) const
{
    if (m_sign)
        return false;
    return m_unsigned_data == other;
}

bool SignedBigInteger::operator!=(const UnsignedBigInteger& other) const
{
    if (m_sign)
        return true;
    return m_unsigned_data != other;
}

bool SignedBigInteger::operator<(const UnsignedBigInteger& other) const
{
    if (m_sign)
        return true;
    return m_unsigned_data < other;
}

FLATTEN SignedBigInteger SignedBigInteger::shift_left(size_t num_bits) const
{
    return SignedBigInteger { m_unsigned_data.shift_left(num_bits), m_sign };
}

FLATTEN SignedBigInteger SignedBigInteger::multiplied_by(const SignedBigInteger& other) const
{
    bool result_sign = m_sign ^ other.m_sign;
    return { m_unsigned_data.multiplied_by(other.m_unsigned_data), result_sign };
}

FLATTEN SignedDivisionResult SignedBigInteger::divided_by(const SignedBigInteger& divisor) const
{
    // Aa / Bb -> (A^B)q, Ar
    bool result_sign = m_sign ^ divisor.m_sign;
    auto unsigned_division_result = m_unsigned_data.divided_by(divisor.m_unsigned_data);
    return {
        { move(unsigned_division_result.quotient), result_sign },
        { move(unsigned_division_result.remainder), m_sign }
    };
}

void SignedBigInteger::set_bit_inplace(size_t bit_index)
{
    m_unsigned_data.set_bit_inplace(bit_index);
}

bool SignedBigInteger::operator==(const SignedBigInteger& other) const
{
    if (is_invalid() != other.is_invalid())
        return false;

    if (m_unsigned_data == 0 && other.m_unsigned_data == 0)
        return true;

    return m_sign == other.m_sign && m_unsigned_data == other.m_unsigned_data;
}

bool SignedBigInteger::operator!=(const SignedBigInteger& other) const
{
    return !(*this == other);
}

bool SignedBigInteger::operator<(const SignedBigInteger& other) const
{
    if (m_sign ^ other.m_sign)
        return m_sign;

    if (m_sign)
        return other.m_unsigned_data < m_unsigned_data;

    return m_unsigned_data < other.m_unsigned_data;
}

}