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SBB
SUBTRACT WITH
BORROW
SBB
Operation:
if
(CF) = 1
then
(DEST) =
(LSRC)-
(RSRC) -1
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
2-147
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.