MOV #0, AC0 ;
MOV #0, AR0 ;

while:
BCC done, AC0 != #0 ;
SFTL AC1, #-1 ;
BCC zeroMaskBit, CARRY ;
ADD #1, AR0 ;
SFTL AC2, #-1 ;
XCC while, CARRY ;
BNOT AC0, AR0;
zeroMaskBit:
SFTL AC2, #-1 ;
B while ;

done: ...