bignum bignum_popzeroes(bignum& c)
{
if (c.size() > 1)
{
while (c.size() > 1 && c.back() == 0)
c.pop_back();
}
return c;
}
void bignum_print(ostream& print, bignum& c)
{
c = bignum_popzeroes(c);
cout << c.back();
if (c.size() - 2 >= 0)
{
for (unsigned int i = c.size()-2; i + 1 > 0; i--)
cout << setfill('0') << setw(3) << c[i];
}
}
bignum bignum_subtract(bignum& a, bignum& b)
{
bignum c;
if (b.size() > a.size())
c.push_back(0);
else if (a.size() == b.size() && b.back() > a.back())
c.push_back(0);
else
{
int k;
for (unsigned int i = 0; i < a.size() + b.size(); i++)
{
k = 0;
if (i < a.size())
k += a[i];
if (i < b.size())
k -= b[i];
c.push_back(k);
}
for (unsigned int i = 0; i < c.size() - 1; i++)
{
while (c[i] < 0)
{
c[i + 1] -= 1;
c[i] += BASE;
}
}
}
c = bignum_popzeroes(c);
return c;
}
bignum bignum_multiply(bignum& a, bignum& b)
{
bignum c(a.size() + b.size() + 1);
for (unsigned int i = 0; i < a.size(); i++)
{
for (unsigned int j = 0; j < b.size(); j++)
{
c[i + j] += a[i] * b[j];
}
c = bignum_carry(c);
}
c = bignum_popzeroes(c);
return c;
}
bool operator<(const bignum& a, const bignum& b)
{
if (a.sign and !b.sign)
return true;
if (!a.sign and b.sign)
return false;
// same sign
if (a.size() != b.size())
// a is shorter XOR a is negative
return (a.size() < b.size()) != a.sign;
// also same length
pair<b_crit, b_crit> m = mismatch(a.rbegin(), a.rend(), b.rbegin());
if (m.first == a.rend())
return false; // a == b
return (*m.first < *m.second) != a.sign;
}
bignum operator*(const bignum& a, const bignum& b)
{
if (a.empty() or b.empty())
return bignum();
if (a.size() + b.size() < 19) {
long long x = a;
long long y = b;
return x*y;
}
const unsigned n = max(a.size(), b.size());
const unsigned h = n/2;
bignum w, x; // a = 10^h * w + x
bignum y, z; // b = 10^h * y + z
b_cit ha, hb;
ha = (h > a.size()) ? a.end() : a.begin()+h;
hb = (h > b.size()) ? b.end() : b.begin()+h;
x.assign(a.begin(), ha);
w.assign(ha, a.end());
x.clean();
w.clean();
z.assign(b.begin(), hb);
y.assign(hb, b.end());
z.clean();
y.clean();
bignum p = w*y;
bignum q = x*z;
bignum r = (w+x) * (y+z);
// result = 10^(2*h) * p + 10^h * (r-p-q) + q
bignum result;
result.resize(a.size() + b.size());
fill(result.begin(), result.begin()+2*h, 0);
copy(p.begin(), p.end(), result.begin() + 2*h);
result.clean();
r -= p+q;
// p = 10^h * r
p.resize(r.size() + h);
fill(p.begin(), p.begin()+h, 0);
copy(r.begin(), r.end(), p.begin()+h);
p.clean();
result += q;
result += p;
result.sign = a.sign != b.sign;
return result;
}
// a += b, ignoring signal
void add_inplace(bignum& a, const bignum& b)
{
a.resize( 1 + max(a.size(), b.size()) );
b_it i;
b_cit j;
Digit carry = 0;
for (i=a.begin(), j=b.begin();
i!=a.end();
++i) {
*i += (j!=b.end() ? *j++ : 0) + carry;
if (*i >= bignum::base) {
*i -= bignum::base;
carry = 1;
} else
carry = 0;
}
assert(carry == 0);
a.clean();
}
bool bignum::operator<(bignum a)
{
if(this->sign() != a.sign())
{
if(this->sign()=='-')
return true;
else
return false;
}
if(this->size()>a.size())
return false;
if(this->size()<a.size())
return true;
for(int i=0;i<a.size();i++)
{
if(this->x.num[i]<a.x.num[i])
return true;
}
return false;
}
bignum bignum_add(bignum& a, bignum& b)
{
bignum c;
int k;
for (unsigned int i = 0; i < a.size() + b.size(); i++)
{
k = 0;
if (i < a.size())
k += a[i];
if (i < b.size())
k += b[i];
c.push_back(k);
}
c = bignum_carry(c);
c = bignum_popzeroes(c);
return c;
}
bignum bignum_carry(bignum& c)
{
for (unsigned int i = 0; i < c.size() - 1; i++)
{
if (c[i] >= BASE)
{
c[i + 1] += c[i] / BASE;
c[i] = c[i] % BASE;
}
}
return c;
}
bool operator==(const bignum& a, const bignum& b)
{
return a.sign == b.sign and
a.size() == b.size() and
equal(a.begin(), a.end(), b.begin());
}
