_magAddSub

private fn

void _magAddSub(int  PrecisionDigits,  bool  sub)(
       ref  ubyte[16]  ma,  ref  bool  nega,  ubyte[16]  mb,
       const  bool  negb)

@safe pure

Adds or subtracts aligned signed magnitudes (sign applied to b is flipped for subtraction). On return ma/nega hold the result.

FixedDecimalException when the magnitude sum exceeds the decimal

precision.