[A86] Re: TI-86 menu routine
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[A86] Re: TI-86 menu routine
Thanks a lot!! This really helps! When I finish the routine I will
probably publish it to this mailing list, so that you can find the bugs
I didnt find. :)
Thanks agian
Michael
Ricky Cobb wrote:
>>ld b,0xh
>> ; here i need to check if a < b
>>
>
> cp b ; update flags
> jr c,CutNow ;if a<b goto CutNow, (or jP if the lable is farther away)
> sub b
>
>> ; if a < b, then jp CutNow
>> ; if a is not less than b, then sub b
>>jp Loop
>>
>
>
>A carry occurs when one number subtracted from the other number has been
>'flipped' around (in other words 2-3 = -1 but one byte can only represent 0-255
>so the carry flag tells when the number subtracted from the other is greater
>than or less than the other.
>
>NC (no carry) is the same as >= (greater than or equal to). It happens when
>either the number your comparing is of equal value (resulting subtraction = 0)
>or it is greater than the number.
>
>If you want to compare just > (greater than but not equal to) then increase the
>number youre comparing a to by 1.
>
>ex.
>;a=6
> cp 5
> jr nc,aisgreaterthan5
>
>;a=5
> cp 5
> jr nc,aisgreaterthanorequalto5
>
>;a=4
> cp 5
> jr c,aislessthan5
>
>;a=4
> cp 4
> jr c,aislessthanorequalto4
> jr z,aislessthanorequalto4
>
>
>
>The cp command does not change the register values but it does perform the same
>operation as the sub command. Basically, it subtracts the number from the other
>(a-number_comparing_to or hl-number_comparing_to) then it updates the flags.
>The register contents at this point are not changed. The sub command will do
>the same thing but the contents of the registers are changed. So if you plan on
>doing a 'sub b' after up there and if you are planning on doing a sub b at
>CutNow then you could optimize the above by using sub b instead of cp b because
>the flags are still updated and you wouldnt need the extra sub b's.
>
>I also wrote a piece about comparing signed numbers (negative 8bit numbers)
>on this mailing list. So if you want to search for that to understand the p and
>m flags for negative comparisons go right ahead :)
>
>
>Hope this helps,
>
>Ricky Cobb
>http://tip.ti-programmers.com/
>arcadesdude@intercom.net
>[IM]
>icq 41440378
>msn arcadesdude
>y! arcadesdude
>aim arcadesdude
>
>8/24/02 8:31:51 AM, Michael Williams <spacex@williams-net.org> wrote:
>
>>Hey all!
>>
>> I havent said anything so far, but I have learned alot from you
>>guys. Thanks!
>>Anyways, I have a problem, Im trying to make a TI-86 assembly menu routine
>>that does the same thing as the Menu( basic command. I've run into a
>>little hiccup though.
>>I need to find out if register a is less than register b. How do I do this?
>>Thanks a lot for your help.
>>
>>Michael Williams
>>
>>PS. This is what it looks like now
>>
>>CutString:
>>ld de,hl-01h ;hl -> string to be cut
>>ld a,17h ; 17h is the number of pixels we have
>>Loop:
>>inc de
>>ld b,(de)
>>cp b, ; All the characters that would cause the string
>>to terminate
>>jp z, CutNow
>>cp b, ; All the characters that are six pixels wide
>>jp z, Minus6
>>
>>....
>>....
>>
>>CutNow:
>>ld (de), 00h
>>ret
>>
>>Minusx: ; this is the same func for all the different
>>pixelwidths, just cut and pasted
>> ; x is between 1 and 6
>>ld b,0xh
>> ; here i need to check if a < b
>> ; if a < b, then jp CutNow
>> ; if a is not less than b, then sub b
>>jp Loop
>>
>>
>>
>>
>>
>>
>
>
>
References: