[A83] Re: Question(bit checking)
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[A83] Re: Question(bit checking)
If it isn't required have the value be dynamic in A (doesn't seem like it
would be for most applications), then of course you could just check it with
bit x,[hl].
-----Original Message-----
From: assembly-83-bounce@lists.ticalc.org
[mailto:assembly-83-bounce@lists.ticalc.org]On Behalf Of
ComAsYuAre@aol.com
Sent: Saturday, July 07, 2001 8:19 AM
To: assembly-83@lists.ticalc.org
Subject: [A83] Re: Question(bit checking)
The only thing about that is it uses non-standard numbering for the bits,
going from 1 (the right-most bit) to 8 (the left-most) rather than 0 to 7.
However, as long as you document this, that should work well enough. It
should be noted, however, that speed fluctuates rather significantly
(proportional to the total execution time) based on which bit you're using.
Consider the following constant-speed alternative:
;hl -> byte
;a = bit # to check, 0-7
;z flag indicates whether bit is 0 or 1
BitCheck:
rlca ;4
rlca ;4
rlca ;4
or %01000110 ;7
ld ($+3),a ;13
bit 0,(hl) ;12
ret ;10
Total: 54 t-states.
In a message dated 7/7/2001 8:32:53 AM Eastern Daylight Time,
tijlc@hotmail.com writes:
> Another option might be this:
>
> ; input: hl->number to check; b=bit to check
> ; output: nz if flag is set
>
> BitFinder:
> ld a,%10000000
> BitFinderLoop:
> rlca
> djnz BitFinderLoop
> and (hl)
> ret
>
----
Jonah Cohen
<ComAsYuAre@aol.com>
http://jonah.ticalc.org
References: