Hi Ted,
Your technique is almost exactly what I use in two small little Cobol
routines that I placed in an XL and forever have access to anytime I want to
create a "special" byte or discern the bit pattern in a byte.
The source listing is below.
Eric Sand
[log in to unmask]
1 $CONTROL NOWARN,DYNAMIC,POST85
1.1 IDENTIFICATION DIVISION.
1.2 PROGRAM-ID. DRAXL026.
1.3 *AUTHOR. ERIC SAND.
1.4 *INSTALLATION. DRA MONTEREY, CALIF.
1.5 *DATE-WRITTEN. 03-01-81.
1.6 DATE-COMPILED.
1.7 ***************************************************
1.8 * PACK AND UNPACK BITS AND BYTE *
1.9 ***************************************************
2 ENVIRONMENT DIVISION.
2.1 CONFIGURATION SECTION.
2.2 SOURCE-COMPUTER. HP-3000.
2.3 OBJECT-COMPUTER. HP-3000.
2.4 SPECIAL-NAMES.
2.5 CONDITION-CODE IS C-C.
2.6 DATA DIVISION.
2.7 WORKING-STORAGE SECTION.
2.8 01 I PIC S9(4) COMP VALUE +0.
2.9 01 J PIC S9(4) COMP VALUE +0.
3 01 FORM-WORD.
3.1 05 FORM-WORD-1 PIC X
3.2 VALUE %0.
3.3 05 FORM-BYTE9 PIC 9.
3.4 05 FORM-BYTE REDEFINES FORM-BYTE9
3.5 PIC X.
3.6 01 FORM-WORD9 REDEFINES FORM-WORD
3.7 PIC 9(4) COMP.
3.8 LINKAGE SECTION.
3.9 01 LS-BYTE PIC X.
4 01 LS-BYTE9 REDEFINES LS-BYTE
4.1 PIC 9.
4.2 01 LS-8BYTES.
4.3 05 LS-8BYTE OCCURS 8 TIMES
4.4 PIC X.
4.5 PROCEDURE DIVISION USING LS-BYTE
4.6 LS-8BYTES.
4.7 *
4.8 BYTE-PACK.
4.9 BP-1.
5 ENTRY "BYTEPACK'026" USING LS-BYTE
5.1 LS-8BYTES.
5.2 MOVE LOW-VALUES TO FORM-WORD.
5.3 MOVE 128 TO J.
5.4 MOVE 1 TO I.
5.5 PERFORM BP-2 8 TIMES.
5.6 MOVE FORM-BYTE TO LS-BYTE.
5.7 GOBACK.
5.8 BP-2.
5.9 IF LS-8BYTE(I) = "1"
6 ADD J TO FORM-WORD9.
6.1 DIVIDE 2 INTO J.
6.2 ADD 1 TO I.
6.3 *
6.4 BYTE-UNPACK.
6.5 BU-1.
6.6 ENTRY "BYTEUNPACK'026" USING LS-BYTE
6.7 LS-8BYTES.
6.8 MOVE SPACES TO LS-8BYTES.
6.9 MOVE LS-BYTE TO FORM-BYTE.
7 PERFORM BU-2
7.1 VARYING I FROM 8 BY -1 UNTIL I < 1.
7.2 GOBACK.
7.3 BU-2.
7.4 DIVIDE 2 INTO FORM-WORD9
7.5 GIVING FORM-WORD9 REMAINDER J.
7.6 IF J > ZERO
7.7 MOVE "1" TO LS-8BYTE(I)
7.8 ELSE
7.9 MOVE "0" TO LS-8BYTE(I).
> -----Original Message-----
> From: Ted Ashton [SMTP:[log in to unmask]]
> Sent: Friday, December 01, 2000 11:28 AM
> To: [log in to unmask]
> Subject: Re: [HP3000-L] Math Help
>
> Thus it was written in the epistle of Porter, Allen H,
> > OK, I'm trying to figure this out but I cannot remember how to do the
> math
> > behind it.
> >
> > If I have a series such as
> > 1
> > 2
> > 4
> > 8
> > 16
> > 32
> > 64
> > 128
> >
> > and I add any combination of these numbers together (4 + 16 = 20) the
> only
> > way I can come up with the number 20 is by adding 4 and 16. Now how do
> I do
> > this in reverse? If I know the sum is 81, how do I determine that the
> > numbers that make up this sum are 1 + 16 + 64?
> >
> > Thanks to anyone with the solution.
>
> As you've already heard the typical solution, here's another one for the
> amusement of it:
>
> Take your number, divide by 2 repeatedly until you reach 0, writing down
> the
> remainders. Simultaneously, write down the successive powers of two:
>
> 81 / 2 = 40 r 1 1
> 40 / 2 = 20 2
> 20 / 2 = 10 4
> 10 / 2 = 5 8
> 5 / 2 = 2 r 1 16
> 2 / 2 = 1 32
> 1 / 2 = 0 r 1 64
>
> In the cases where there are remainders, multiply the remainders by the
> associated power of two and you have the desired 1 + 16 + 64. This will
> also work for other powers:
>
> 81 / 5 = 16 r 1 1
> 16 / 5 = 3 r 1 5
> 3 / 5 = 0 r 3 25
>
> giving 81 = 1 + 5 + 75
>
> Oddly enough, there are times when going at it "backwards" like this is
> preferable.
>
> Ted
> --
> Ted Ashton ([log in to unmask]), Info Sys, Southern Adventist University
> ==========================================================
> Men pass away, but their deeds abide.
> -- Cauchy, Augustin-Louis (1789 -
> 1857)
> ==========================================================
> Deep thoughts to be found at http://www.southern.edu/~ashted
|
