static int Compare(Bignum a, Bignum b)
{
int bigit_length_a = a.BigitLength();
int bigit_length_b = b.BigitLength();
if (bigit_length_a < bigit_length_b)
{
return(-1);
}
if (bigit_length_a > bigit_length_b)
{
return(+1);
}
for (int i = bigit_length_a - 1; i >= System.Math.Min(a.exponent_, b.exponent_); --i)
{
uint bigit_a = a.BigitAt(i);
uint bigit_b = b.BigitAt(i);
if (bigit_a < bigit_b)
{
return(-1);
}
if (bigit_a > bigit_b)
{
return(+1);
}
// Otherwise they are equal up to this digit. Try the next digit.
}
return(0);
}
internal static int PlusCompare(Bignum a, Bignum b, Bignum c)
{
Debug.Assert(a.IsClamped());
Debug.Assert(b.IsClamped());
Debug.Assert(c.IsClamped());
if (a.BigitLength() < b.BigitLength())
{
return(PlusCompare(b, a, c));
}
if (a.BigitLength() + 1 < c.BigitLength())
{
return(-1);
}
if (a.BigitLength() > c.BigitLength())
{
return(+1);
}
// The exponent encodes 0-bigits. So if there are more 0-digits in 'a' than
// 'b' has digits, then the bigit-length of 'a'+'b' must be equal to the one
// of 'a'.
if (a.exponent_ >= b.BigitLength() && a.BigitLength() < c.BigitLength())
{
return(-1);
}
uint borrow = 0;
// Starting at min_exponent all digits are == 0. So no need to compare them.
int min_exponent = System.Math.Min(System.Math.Min(a.exponent_, b.exponent_), c.exponent_);
for (int i = c.BigitLength() - 1; i >= min_exponent; --i)
{
uint chunk_a = a.BigitAt(i);
uint chunk_b = b.BigitAt(i);
uint chunk_c = c.BigitAt(i);
uint sum = chunk_a + chunk_b;
if (sum > chunk_c + borrow)
{
return(+1);
}
else
{
borrow = chunk_c + borrow - sum;
if (borrow > 1)
{
return(-1);
}
borrow <<= kBigitSize;
}
}
if (borrow == 0)
{
return(0);
}
return(-1);
}
