mirror of
https://github.com/deater/dos33fsprogs.git
synced 2025-01-31 18:31:48 +00:00
169 lines
2.0 KiB
ArmAsm
169 lines
2.0 KiB
ArmAsm
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; by Vince `deater` Weaver <vince@deater.net>
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; calculating (X^Y) % 9
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; zero page
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GBASH = $27
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MASK = $2E
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COLOR = $30
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XX = $F7
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OFFSET = $F8
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YY_OFFSET= $F9
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YY = $FA
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OLD = $FE
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TEMP = $FF
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; Soft switches
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FULLGR = $C052
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PAGE1 = $C054
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PAGE2 = $C055
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LORES = $C056 ; Enable LORES graphics
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; ROM routines
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HGR = $F3E2
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HGR2 = $F3D8
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PLOT = $F800 ; PLOT AT Y,A
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PLOT1 = $F80E ; PLOT at (GBASL),Y (need MASK to be $0f or $f0)
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GBASCALC= $F847 ; take Y-coord/2 in A, put address in GBASL/H ( a trashed, C clear)
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SETCOL = $F864 ; COLOR=A
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SETGR = $FB40
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;================================
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; Clear screen and setup graphics
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;================================
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other:
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jsr SETGR
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bit FULLGR
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lda #0
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sta OFFSET
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looper:
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lda OFFSET
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sta YY_OFFSET
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ldx #47
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stx YY
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yloop:
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ldy #39
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lda YY
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; txa ; YY ; plot call needs Y/2
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lsr
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php
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jsr GBASCALC ; take Y-coord/2 in A, put address in GBASL/H ( a trashed, C clear)
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lda GBASH
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draw_page_smc:
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adc #0
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sta GBASH ; adjust for PAGE1/PAGE2 ($400/$800)
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plp
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jsr $f806 ; trick to calculate MASK by jumping
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; into middle of PLOT routine
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xloop:
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tya
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clc
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adc OFFSET
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eor YY_OFFSET
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jsr mod_9
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beq its_zero
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lda #0
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jmp setcolor
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its_zero:
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lda #6
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setcolor:
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jsr SETCOL
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txa
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jsr PLOT1 ; plot at Y,A (A trashed, XY Saved)
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dey
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bpl xloop
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inc YY_OFFSET
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ldx YY
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dex
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stx YY
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bpl yloop
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end:
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ldx #0
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flip_pages:
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lda draw_page_smc+1 ; DRAW_PAGE
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beq done_page
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inx
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done_page:
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ldy $C054,X ; set display page to PAGE1 or PAGE2
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eor #$4 ; flip draw page between $400/$800
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sta draw_page_smc+1 ; DRAW_PAGE
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inc OFFSET
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jmp looper
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;===============================
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; modulo 9
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;===============================
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; value in A
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mod_9:
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; Divide by 9
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; 17 bytes, 30 cycles
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; by Omegamatrix https://forums.nesdev.com/viewtopic.php?t=11336
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sta OLD
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sta TEMP
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lsr
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lsr
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lsr
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adc TEMP
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ror
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adc TEMP
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ror
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adc TEMP
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ror
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lsr
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lsr
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lsr
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; A is ORIG/9, mod = OLD-(A*9)
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sta TEMP
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asl
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asl
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asl
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clc
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adc TEMP
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eor #$ff
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sec
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adc OLD
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rts
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; want this at $3F5, this is $80 in, so $375
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jmp other
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