123 lines
2.2 KiB
ArmAsm
123 lines
2.2 KiB
ArmAsm
; Entropy
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; by Dave McKellar of Toronto
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; Two-line BASIC program
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; Found on Beagle Brother's Apple Mechanic Disk
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; Converted to 6502 Assembly by Deater (Vince Weaver) vince@deater.net
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; 24001 ROT=0:FOR I=1 TO 15: READ A,B: POKE A,B: NEXT: DATA
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; 232,252,233,29,7676,1,7678,4,7679,0,7680,18,7681,63,
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; 7682,36,7683,36,7684,45,7685,45,7686,54,7687,54,7688,63,
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; 7689,0
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; 24002 FOR I=1 TO 99: HGR2: FOR E=.08 TO .15 STEP .01:
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; FOR Y=4 to 189 STEP 6: FOR X=4 to 278 STEP 6:
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; SCALE=(RND(1)<E)*RND(1)*E*20+1: XDRAW 1 AT X,Y:
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; NEXT: NEXT: NEXT: NEXT
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; SCALE=(RND(1)<E)*RND(1)*E*20+1
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;
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; Equivalent to IF RND(1)<E THEN SCALE=RND(1)*E*20+1
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; ELSE SCALE=1
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; What this does:
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; if EPOS is 8,9 then value is either 1 or 2
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; if EPOS is 10,11,12,13,14 then value is either 1, 2, or 3
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; Optimization
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; 88 bytes -- hack up the entropy code
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; 83 bytes -- count down YPOS instead of up
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; 73 bytes -- XPOS only up to 256
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; 73 bytes -- move to zero page
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; 65 bytes -- move XPOS/YPOS into X/Y, use RESTORE
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;BLT=BCC, BGE=BCS
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; zero page locations
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HGR_SHAPE = $1A
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A5H = $45
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XREG = $46
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YREG = $47
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HGR_SCALE = $E7
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HGR_ROTATION = $F9
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FRAME = $FC
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XPOS = $FD
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YPOS = $FF
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; ROM calls
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HGR2 = $F3D8
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HPOSN = $F411
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XDRAW0 = $F65D
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RESTORE = $FF3F
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.zeropage
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entropy:
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jsr HGR2 ; Hi-res graphics, no text at bottom
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; Y=0, A=0 after this call
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eloop:
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ldy #180 ; Y=180 down to 0 STEP 6
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yloop:
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ldx #4 ; FOR X=4 to 278 STEP 6
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xloop:
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frame_smc:
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lda $D000 ; 3 ; also FRAME
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and #1 ; 2
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sta HGR_SCALE ; 2
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inc HGR_SCALE ; 2 = 9
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; ldx #1 ; 2
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; ldy FRAME ; 2
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; lda $D000,y ; 3
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; bmi no_add ; 2
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; inx ; 1
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;no_add: ;
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; stx HGR_SCALE ; 2 = 12
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stx XREG ; save X
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sty YREG ; save Y
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; setup X and Y co-ords
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tya ; YPOS into A
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ldy #0 ; Y always 0
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; XPOS already in X
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jsr HPOSN ; X= (y,x) Y=(a)
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ldx #<shape_table ; point to our shape
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lda #0 ; ROT=0
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tay ; ldy #>shape_table
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jsr XDRAW0 ; XDRAW 1 AT X,Y
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; Both A and X are 0 at exit
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jsr RESTORE ; restore FLAGS/X/Y/A
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nextx: ; NEXT X
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inc frame_smc+1
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txa
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clc ; 1
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adc #6 ; x+=6 ; 2
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tax
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bne xloop ; if so, loop ; 2
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nexty:
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; carry always set if we get here
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; sec
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tya
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sbc #6 ; y-=6
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tay
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bne yloop ; if so, loop
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beq eloop
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shape_table:
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.byte 18,63,36,36,45,45,54,54,63,0 ; data
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