on 7/14/02 3:36 PM, Andrew Davie at adavie@xxxxxxxxxxx wrote:
>
>
>> Not necessary, everything looks fine! :-)
>
> The statement that "has to compare a whole byte for each possibility, while
> the second routine compares 1 bit. That's 8 times more efficient (I think).
> " is in error. Comparing a byte against comparing a bit is not 8 times
> less efficient. In fact, it really depends how you do things, and what you
> want to do. Sometimes comparing a bit is less efficient. Depends which
> bit, and if you can modify A, for example. Or if the byte is in memory or a
> register.
>
> For example, if I wanted to check to see if bit 4 was set in A, without
> destroying A...... how do I do that?
> I can't... directly. There's no BIT # instruction. So I have to save the
> value somewhere, bit it, and restore it
>
> sta temp ; save A
> lda #16 ; the bit we want to check
> bit temp ; check the bit
> lda temp ; restore
To test is very simple
Var16 .Byte 16 ;Single byte in ROM, a 16 is here
LDA value ;Get value, optional since it may already be loaded in A
BIT Var16 ;AND with #16, store result of AND in the zero flag
BNE BitIsSet ;BNE if true, BEQ if AND is false
Done.
Burger
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