sub method
void
sub()
Implementation
void sub() {
//Debugger.verbose('${pcHex(-1)} [sub]');
final operands = mem.loadb(programCounter- 1) < 193
? visitOperandsLongForm()
: visitOperandsVar(2, false);
final resultTo = readb();
final result = MathHelper.toSigned(operands[0].value!) - MathHelper.toSigned(operands[1].value!);
//Debugger.verbose(' >>> (sub ${pc.toRadixString(16)}) ${operands[0].value}(${toSigned(operands[0].value)}) - ${operands[1].value}(${toSigned(operands[1].value)}) = $result');
writeVariable(resultTo, result);
}