The routine above divides
A$
into AH and AL
(4
digits) and
B$
into
BH
and
BL
(4
digits):
A$19191919191919191
1 \
AHI91919191
ALI91919191
Step 3: Multiply
AH.
Al.
BH.
and
Bl
into four product strings: P1$,
P2$,
P3$.
and
P4$.
The rules of algebraic multiplication multiply each variable
as
if
it
were a single number.
A$
and
B$
are multiplied
as
follows:
381~
x@jJ
lêII
Think of
A$
and
B$
as
two
sets of
4-digit
numbers
(H
and Ujoined in the middle.
and not
as
eight individual digits:
A$
is
not eight
9s.
but
two
sets of four
9s
each.
Thus AL and
BL
are multiplied
as:
AL
199991
xBL
~
Multiplying
A$
and
B$
is
a four-step process. To begin. multiply
BL
x AL:
~
ffihY
and then
BL
x AH:
Next. move over to
BH
and multiply
BH
by AL:
~
BH
and finally
BH
x AH:
~
'-00
When the
PET
multiplies
BL
x AL. etc.,
it
internally multiplies the values of
BL
and
AL.
Consequently. the
4-digit
values of
BL
and AL
are
multiplied together.
producing the
8-digit
product
P1.
Below
is
the four-step process:
l68J
:?~[g)
~
ŒbJçrm
Œ1J
x@D
BL
x
1§8]
'1ii
x~ŒJ
ffi8J
00
Pl$
Pl$
Pl$
Pl$
P2$
P2$ P2$
P3$
P3$
P4$
2
3
4
217
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