BigInt.fromTwosComplement

private BigInt fromTwosComplement(ulong[] ext, bool negative) static pure @safe

Converts a w-limb two's-complement pattern back into a BigInt.

`ext`	The pattern limbs; consumed (modified in place).
`negative`	The result sign, which must be derived from the operand signs (OR: either, AND: both, XOR: differing).

The signed value the pattern represents.