A83: Re: Setting a bit...

To: <assembly-83@lists.ticalc.org>
Subject: A83: Re: Setting a bit...
From: "David Phillips" <david@acz.org>
Date: Tue, 18 Jan 2000 08:16:46 -0700
References: <000c01bf61ba$87cf8a00$787d883e@default>
Reply-To: assembly-83@lists.ticalc.org


Use a lookup table and an xor operation:

; a = value to change, c = bit to change (starting at 0)
; 8b / 39t (16b total)

 ld b,0
 ld hl,BitMasks
 add hl,bc
 ld b,(hl)
 xor b

BitMasks:
 .db $1, $2, $4, $8, $10, $20, $40, $80



> Ok, question here...what's a good way to toggle the nth bit of a byte when
n is stored in
> a register? For example:
>
>  ld a,3
>
> ;
> ; Necessary code here
> ;
>
> And the 3rd bit is set/reset. I thought of creating a bitmask on-the-fly
then XORing it,
> or perhaps making a lookup table...but I'm still not too sure. Help? :)

Follow-Ups:

Re: A83: Re: Setting a bit...

From: "The Godfather" <HOPPEAL@fs1.usa.k12.mi.us>

References:

A83: Setting a bit...

From: "James Matthews" <jjj@matthewsfamily.fsnet.co.uk>