BigInt.opCmp
Implements 3-way comparisons of BigInt with BigInt or BigInt with built-in numeric types.
int opCmp(T)(const T y) if (isIntegral!T) pure nothrow @nogc @safe constditto
int opCmp(T)(const T y) if (isFloatingPoint!T) nothrow @nogc @safe constditto
ditto