File content as of revision 0:9d554894785b:

#include "BigInt.h"
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <climits>


static uint32_t max(const uint32_t a, const uint32_t b)
{
    return a < b ? b : a;
}

static uint32_t num(const uint32_t a)
{
    return a/4 + (a%4 ? 1:0); 
}
    
BigInt::BigInt():
size(0),
bits(0)
{
}

BigInt::BigInt(const BigInt &a):
size(a.size)
{
    uint32_t l = num(size);
    bits = new uint32_t[l];
    for(int i = 0; i < l; ++i)
        bits[i] = a.bits[i];
}


BigInt::~BigInt()
{
    if(bits)
        delete[] bits;
    bits = 0;
}

BigInt& BigInt::operator=(const BigInt& a)
{
    size = a.size;
    uint32_t l = num(size);
    if(bits)
        delete[] bits;
    bits = new uint32_t[l];
    for(int i = 0; i < l; ++i)
        bits[i] = a.bits[i];    
    return *this;
}

void BigInt::import(uint8_t *data, uint32_t length)
{
    size = length;
    size_t l = size/4;
    if(size % 4 != 0)
        l++;
    if(bits)
        delete[] bits;
    bits = new uint32_t[l];
    memset(bits, 0, sizeof(uint32_t)*l);
    for(int i = 0; i < length; ++i)
        bits[i/4] |= data[i] << ((i%4)*8);
}

BigInt operator+(const BigInt &a, const BigInt& b)
{
    BigInt result;
    
    result.size = a.size > b.size ? a.size : b.size;
    size_t l = result.size/4;
    if(result.size % 4 != 0)
        l++;
    result.bits = new uint32_t[l];
    memset(result.bits, 0, sizeof(uint32_t)*l);
    uint32_t al = num(a.size);
    uint32_t bl = num(b.size);
    uint32_t carry = 0;
    for(int i = 0; i < l; ++i)
    {
        uint32_t tmpA = 0, tmpB = 0;
        if(i < al)
            tmpA = a.bits[i];
        if(i < bl)
            tmpB = b.bits[i];
        result.bits[i] = tmpA + tmpB + carry;
        carry = result.bits[i] < max(tmpA, tmpB);
    }
    if(carry)
    {
        result.size++;
        if(result.size > l*4)
        { 
            l++;
            result.bits = (uint32_t*)realloc(result.bits, l * sizeof(uint32_t));
            result.bits[l-1] = 0x00000001;
        }
        else
        {
            result.bits[l-1] += 1 << (8 *((result.size-1)%4));
        }
    }
    
    return result;
}

BigInt& BigInt::operator+=(const BigInt &b)
{
    return (*this = (*this) + b);
}

BigInt& BigInt::operator++()
{
    uint8_t tmp = 1;
    BigInt a;
    a.import(&tmp, 1);
    
    return (*this += a);
}

BigInt BigInt::operator++(int)
{
    BigInt t = *this;
    uint8_t tmp = 1;
    BigInt a;
    a.import(&tmp, 1);
    this->operator+=(a);
    return t;
}

// a - b, if b >= a, returns 0
// No negative number allowed
BigInt operator-(const BigInt &a, const BigInt& b)
{
    BigInt result;

    if(b >= a)
    {
        uint8_t tmp = 0;
        result.import(&tmp, 1);
        return result;
    }
    else
    {
        result.size = a.size;
        uint32_t l = num(a.size);
        result.bits = new uint32_t[l];
        memset(result.bits, 0, sizeof(uint32_t)*l);
        uint32_t bl = num(b.size);
        uint8_t borrow = 0;
        for(uint32_t i = 0; i < l; ++i)
        {
            uint32_t tmpA = a.bits[i], tmpB = 0;
            if(i < bl)
                tmpB = b.bits[i];
            if(borrow)
            {
                if(tmpA == 0)
                    tmpA = ULONG_MAX;
                else
                    --tmpA;
                    
                if(tmpA < tmpB)            
                    result.bits[i] = tmpA + 1 + (ULONG_MAX - tmpB);
                else
                    result.bits[i] = tmpA - tmpB;

                if(a.bits[i] != 0 && tmpA > tmpB)
                    borrow = 0;
            }
            else
            {
                if(tmpA < tmpB)            
                    result.bits[i] = tmpA + 1 + (ULONG_MAX - tmpB);
                else
                    result.bits[i] = tmpA - tmpB;
                borrow = tmpA < tmpB;
            }
        }
        
        // trim result
        uint8_t *tmp = (uint8_t*)result.bits;
        uint32_t newSize = result.size;
        while(tmp[newSize-1] == 0 && newSize > 0)
            newSize--;
        result.size = newSize;
        uint32_t tmpL = num(result.size);
        if(tmpL < l)
            result.bits = (uint32_t*)realloc(result.bits, sizeof(uint32_t)*tmpL); 
        
        return result;
    }
}

BigInt& BigInt::operator-=(const BigInt &b)
{
    return (*this = (*this) - b);
}

BigInt& BigInt::operator--()
{
    uint8_t tmp = 1;
    BigInt a;
    a.import(&tmp, 1);
    
    return (*this -= a);
}

BigInt BigInt::operator--(int)
{
    BigInt t = *this;
    uint8_t tmp = 1;
    BigInt a;
    a.import(&tmp, 1);
    this->operator-=(a);
    return t;
}

bool operator==(const BigInt &a, const BigInt &b)
{
    if(a.size != b.size)
        return false;
        
    uint32_t l = num(a.size);
    for(int i = 0; i < l; ++i)
        if(a.bits[i] != b.bits[i])
            return false;
    return true;
}

bool operator!=(const BigInt &a, const BigInt &b)
{
    return ! (a==b);
}

bool operator<(const BigInt &a, const BigInt &b)
{
    if(a.size < b.size)
        return true;
    if(a.size > b.size)
        return false;
    uint32_t l = num(a.size);
    for(int i = l-1; i >= 0; --i)
        if(a.bits[i] < b.bits[i])
            return true;
    return false;
}

bool operator<=(const BigInt &a, const BigInt &b)
{
    return (a < b) || (a == b);
}

bool operator>(const BigInt &a, const BigInt &b)
{
    if(a.size > b.size)
        return true;
    if(a.size < b.size)
        return false;
    uint32_t l = num(a.size);
    for(int i = l-1; i >= 0; --i)
        if(a.bits[i] > b.bits[i])
            return true;
    return false;
}

bool operator>=(const BigInt &a, const BigInt &b)
{
    return (a > b) || (a == b);
}

bool BigInt::operator!()
{
    if(size != 1)
        return false;
    return bits[0] == 0;
}
 
void BigInt::print()
{
    printf("size: %d bytes\n", size);
    uint32_t n = num(size);
    for(int i = n-1; i >= 0; --i)
    {
        printf("%08x", bits[i]);
    }
    printf("\n");
}