A83: Sv: What CPIR does! was (No Subject)- corrected

To: <assembly-83@lists.ticalc.org>
Subject: A83: Sv: What CPIR does! was (No Subject)- corrected
From: "Thomas Turn Jensen" <Mukke@get2net.dk>
Date: Wed, 18 Nov 1998 16:59:10 +0100
Delivered-To: assembly-83-outgoing@towerguard.unix.edu.sollentuna.se
Reply-To: assembly-83@lists.ticalc.org


Thanks.. I was really wondering :)

Looking forward to have more time to fool around with this...

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Thomas Turn Jensen
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Får computeren dig til at sukke?
Så kald da blot på Mukke
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-----Oprindelig meddelelse-----
Fra: Ben Wise <bwise@labyrinth.net.au>
Til: assembly-83@lists.ticalc.org <assembly-83@lists.ticalc.org>
Dato: 18. november 1998 02:27
Emne: A83: What CPIR does! was (No Subject)- corrected


>
>Well guys I just thought it should be my turn to explain some source code, I
>hope this helps and that it is correct!!
>
>CPIR
>Ok well as you will remember Pat Milherton's code went like this:
>ld a,(something)
>ld hl,numbers
>ld bc,3
>cpir
>jp z,aroutine
>
>numbers:  db 1,3,65
>
>Which simply performs an
>If a==1 or a==3 or a==65
>Then
>etc..
>End
>Ok so the (something) is what we are comparing to see if it is 1, 3 or 65..
>read Olle's message about parenthesis for info on "(something)"... CPIR
>stands for (IMHO) ComPare, Increment and Repeat....
>Bascially this instruction compares whatever hl points to (again see Olle's
>post on "(something) - parenthesis" with what is in register a...
>This continues until either:
>    bc==0
>    a==(hl)
>where in this case (hl) can be either 1, 3 or 65
>Every time the instrution "repeats":
>    bc is deincremented (e.g. bc=bc-1)
>    hl is _incremented_ (e.g. hl=hl+1) - Hence compare Increment and repeat.
>So to step through that code for the first couple of increments ...
>
>ld a,(something)
>;a will now contain the number 3
>ld hl,numbers
>;hl contains the _address_ of the label numbers
>ld bc,3
>;bc contains the number three, because there are three numbers we want to
>compare a to...
>cpir
>;now the cpir instuction has been fed the correct stuff:
>    ;a=3
>    ;hl = start of numbers
>    ;bc = number of things to compare (3)
>;the CPIR instruction will continue as I said before until a==(hl) or bc=0,
>if a match is found, then CPIR will stop, and set the Zero flag, so:
>jp z,aroutine
>;A match is found in this case since a=3, therefore the code will now branch
>to the code at aroutine
>;code for no match continues here.....
>
>. . .
>. . .
>aroutine:
>the routine etc....
>
>
>numbers:  db 1,3,65
>something: db 3
>
>Ok that's one big post, hope that helps and if you 've got any questions
>email me!
>
>