Commodore PET User Manual page 212

To obtain the high (H) and low (U numeric values for both A$ and B$. use
the following statements:
1000 X=LEN(A$):Y=LEN(B$)
1002 IF X>Y THEN F=X/2:GOTO 1006
1004 F='r',··2
1006 IF F>INT(F) THEN F=INT(F)+l
1008 F$=LEFT$(ZERO$,F)
1010 IF X(=F THEN AH=0:AL=VAL(A$):GOTO 1040
1020 AH=VAL(LEFT$(A$,X-F»
1030 AL=VAL(RIGHT$<A$,F»
1040 IF Y(=F THEN BL=VAL<B$):GOTO 1070
1050 BH=VAL<LEFT$<B$,Y-F»
1060 BL=VAL(RIGHT$<B$,F»
Statements 1010 and 1040 compare the string lengths with the divider point F
(81. If the string is shorter than eight. AH (or BH) is assigned a zero value. leaving
only AL (or BU equal to A$ or B$. If the string is longer than eight it must be
divided into high and low segments: AH or BH - the high segments - are
assigned the value of the leftmost LEN(X or y) minus eight digits at 1020 and
1050.
1020 AH=VAU: LEFT$ (A$, >::-F) )
AH=VAL(LEFT$(A$.16-S))
AH=VAL(LEFT$( 11121314151617IsI9101112131415161.S))
AH=vAL(!1121314151617/sll
AH-(1il1234567SI
To obtain AL. the rightmost eight digits are extracted from A$:
1030 AL=VAL<RIGHT$(A$,F»
AL=VAL(RIGHT$(111213j415i617js19IoI112131415161.s))
AL= VAL 09101112131415161l
AL=111l901234561
The same procedure is used to extract BH and BL. Notice that
the VAL
function converts the strings into numbers.
Step 3: Once the large strings are divided into segments small enough for
the PET to handle.
addition
can begin. Multiple integer addition adds correspond-
ing groups of numbers by adding AH and BH together and AL and BL together.
Whole groups of digits are added. instead of individual numbers. When a number
is handled as a group of digits and not as a numeric string. the addition of each
number does not have to be done digit by digit as with the numeric string
method.
The PET can add numbers, whereas it is unable to adct numeric
strings.
AH 11il1234567S1
+BH Ililooooooool
CH 11il1234567S1
AL 11il901234561
+BL 11il579435721
CL 11il14S06702S1
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