Random-Cpp/NegBin/NegBin.cpp

//
// Created by trotfunky on 04/11/2020.
//

#include <iostream>
#include "NegBin.h"


NegBin::NegBin(longBitField binaryRepresentation) :
    value(binaryRepresentation.to_ulong())
{}

NegBin::NegBin(long decimalValue) : value(0)
{
    unsigned int currentPower = 0;
    decimalValue *= -1;
    // This works by checking the remainder by -2, giving the lowest bit of the converted number.
    // Then, shift to the right to drop the bit we just checked and start again until every set bit has been checked.
    // The sign flips each time as we are in base -2 and not 2.
    // Miiight be UDB...
    while (decimalValue != 0)
    {
        value |= std::abs(decimalValue%-2) << currentPower;
        decimalValue = -decimalValue >> 1;
        currentPower++;
    }
}

NegBin& NegBin::operator+=(const NegBin& rhs)
{
    unsigned long carry = 0;

    for(unsigned int i = 0;i<sizeof(long)*8;i++)
    {
        unsigned long temp_carry = carry >> i;
        unsigned long temp_rhs = rhs.value >> i;
        unsigned long temp_lhs = this->value >> i;

        // Nothing remaining to add
        if (!(temp_rhs | temp_carry)) break;

        // Both carry and right hand side are 1 so we need to add a carry
        if (temp_carry & temp_rhs & 1)
        {
            // If the carry is already set for this bit, it needs to be cleared for this bit and the next
            if (temp_carry >> 1 & 1)
            {
                carry &= ~(0b11 << i);
            }
            else
            {
                // Else add a two bit carry
                carry |= 0b11 << (i+1);
            }
        }
        // If either of them are set, add to lhs, otherwise don't bother
        else if ((temp_carry ^ temp_rhs) & 1)
        {
            // If a carry was already set for the next bit too, discard both carries and the current bit
            if (temp_lhs & temp_carry & 1 && temp_carry >> 1 & 1)
            {
                carry &= ~(0b11 << i);
                this->value &= ~(0b1 << i);
            }
            else if (temp_lhs & 1)
            {
                // If the current bit was set, clear and add a two bit carry
                carry |= 0b11 << (i+1);
                this->value &= ~(0b1 << i);
            }
            else
            {
                this->value |= 0b1 << i;
            }
        }
    }
    return *this;
}

NegBin operator+(NegBin lhs, const NegBin& rhs)
{
    lhs += rhs;
    return lhs;
}

NegBin& NegBin::operator-=(const NegBin& rhs)
{
    // lhs - rhs <=> lhs + (-rhs)
    *this += ~rhs;
    return *this;
}

NegBin operator-(NegBin lhs, const NegBin& rhs)
{
    lhs -= rhs;
    return lhs;
}

NegBin& NegBin::operator*=(const int& rhs)
{
    auto unit = *this;
    for (int i=0;i<rhs;i++)
    {
        *this += unit;
    }
    return *this;
}

NegBin operator*(NegBin lhs, const int& rhs)
{
    lhs *= rhs;
    return lhs;
}

NegBin operator*(const int& lhs, NegBin rhs)
{
    return rhs*lhs;
}

NegBin NegBin::operator~() const
{
    // Shifting to the right is equivalent to dividing by the base. As we are using base -2,
    // multiplying by 2 and shifting to the right gives us the opposite of the number.
    return (*this+*this) >> 1;
}

NegBin NegBin::operator>>(const int& rhs)
{
    this->value >>= rhs;
    return *this;
}

NegBin NegBin::operator<<(const int& rhs)
{
    this->value <<= rhs;
    return *this;
}

NegBin::operator long() const
{
    long result = 0;
    for(unsigned int i = 0;i<sizeof(long)*8;i++)
    {
        result += ((value >> i) & 1)*std::pow(-2,i);
    }
    return result;
}

NegBin operator ""_nb(unsigned long long number)
{
    return NegBin(longBitField(number));
}

std::ostream& operator<<(std::ostream& ostream, const NegBin& number)
{
    ostream << static_cast<long>(number);
    return ostream;
}