Re: A83: Re: Negative or positive?

To: <assembly-83@lists.ticalc.org>
Subject: Re: A83: Re: Negative or positive?
From: "Harper Maddox" <gte172i@prism.gatech.edu>
Date: Wed, 1 Mar 2000 15:20:59 -0500
References: <Pine.LNX.4.21.0003012012340.608-100000@localhost>
Reply-To: assembly-83@lists.ticalc.org


;**********
;*original*
;**********
; always works

 ld a,r                ; or insert your favorite random number routine
 rra
 jr nc,increaseSpeed   ; move right if A=1

 ld a,(speed)
 dec a
 cp 6
 jr z,skipChangeSpeed  ; dont change speed
 ld (speed),a

 jr skipChangeSpeed    ; dont want to increase it either

increaseSpeed:
 ld a,(speed)
 inc a
 cp 90
 jr z,skipChangeSpeed  ; dont change speed
 ld (speed),a

skipChangeSpeed:


;*****************************
;*Done using negative numbers*
;*****************************
; half the time it is skipped. (on r = 1 and r = 3)

 ld a,r
 and %11        ; 0 to 3
 jr z,skipIT    ; throw out 3

 dec a          ; -1 to 1
 ld b,a
 ld a,(speed)
 add a,b
 cp 6
 jr c,skipIT
 cp 90
 jr nc,skipIT

 ld (speed),a

skipIT:

References:

Re: A83: Re: Negative or positive?

From: Linus Akesson <lairfight@softhome.net>

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