src/N.Substraction.cpp

#include <symbolism/N.h>
#include <string>
#include <sstream>

using namespace std;

namespace symbolism {
namespace ring {

void N::sub_large_large(const N& a, const N& b)
{
    limb_t borrow;
    reserve(max(a.size, b.size));
    if(a.size > b.size)
    {
        borrow = mpn_sub(data, a.data, a.size + 1, b.data, b.size + 1);
    }
    else if(a.size == b.size)
    {
        borrow = mpn_sub_n(data, a.data, b.data, a.size + 1);
    }
    else
    {
        borrow = mpn_sub(data, b.data, b.size + 1, a.data, a.size + 1);
    }
    if(borrow)
    {
        throw result_negative_exception(__FILE__, __LINE__);
    }
    normalize();
}

void N::sub_large_large(const N& a)
{
    N::limb_t borrow;
    if(size > a.size)
    {
        borrow = mpn_sub(data, data, size + 1, a.data, a.size + 1);
    }
    else if(size == a.size)
    {
        borrow = mpn_sub_n(data, data, a.data, size + 1);
    }
    else
    {
        throw result_negative_exception(__FILE__, __LINE__);
    }
    if(borrow)
    {
        throw result_negative_exception(__FILE__, __LINE__);
    }
    normalize();
}

void N::sub_large_small(const N& a, const N::limb_t b)
{
    N::limb_t borrow;
    reserve(a.size);
    borrow = mpn_sub_1(data, a.data, a.size + 1, b);
    if(borrow)
    {
        throw result_negative_exception(__FILE__, __LINE__);
    }
    normalize();
}

void N::sub_large_small(const N::limb_t a)
{
    N::limb_t borrow;
    borrow = mpn_sub_1(data, data, size + 1, a);
    if(borrow)
    {
        throw result_negative_exception(__FILE__, __LINE__);
    }
    normalize(); // Chance of unormalization is small
}

void N::sub_one_large()
{
    limb_t borrow = 1;
    for(size_t i=0; i <= size && borrow; i++)
    {
        limb_t old = data[i];
        data[i] -= borrow;
        borrow = (limb > old) ? 1 : 0;
    }
    if(borrow)
    {
        throw result_negative_exception(__FILE__, __LINE__);
    }
}

}}

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