SBB
SUBTRACT WITH
BORROW
SBB
Operation:
if (CF) = 1 then (DEST) = (LSRC)- (RSRC)
else (DEST) - (LSRC) - (RSRC)
Description:
see destination,source
SBB (Subtract w.ith Borrow) subtracts the source from the destination, subtracts one if CF is set, and returns the result to the destina- tion operand. Both operands may be bytes or words. Both operands may be signed or
Flags Affected:
AF,CF,OF,PF,SF,ZF
unsigned binary numbers (see AAS and DAS). SBB updates AF,· CF, OF, PF, SF, and ZF. Since it incorporates a borrow from a previous operation, SBB may be used to write routines that subtract numbers longer than 16 bits.
