mirror of
https://github.com/deater/dos33fsprogs.git
synced 2024-07-15 19:29:07 +00:00
76 lines
943 B
ArmAsm
76 lines
943 B
ArmAsm
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; thick sine
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; zero page
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GBASL = $26
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GBASH = $27
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YY = $69
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ROW_SUM = $70
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HGR_X = $E0
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HGR_XH = $E1
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HGR_Y = $E2
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HGR_COLOR = $E4
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HGR_PAGE = $E6
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FRAME = $FC
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SUM = $FD
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SAVEX = $FE
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SAVEY = $FF
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thick_sine:
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;==================
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; create sinetable
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ldy #0 ; Y is 0
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sinetable_loop:
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tya ; 2
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and #$3f ; wrap sine at 63 entries ; 2
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cmp #$20
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php ; save pos/negative for later
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and #$1f
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cmp #$10
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bcc sin_left ; blt
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sin_right:
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; sec carry should be set here
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eor #$FF
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adc #$20 ; 32-X
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sin_left:
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tax
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lda sinetable_base,X ; 4+
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plp
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bcc sin_done
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sin_negate:
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; carry set here
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eor #$ff
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adc #0 ; FIXME: this makes things off by 1
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sin_done:
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sta sinetable,Y
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iny
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bne sinetable_loop
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; Y is 0 at this point?
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done:
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jmp done
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sinetable_base:
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; this is actually (32*sin(x))
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.byte $00,$03,$06,$09,$0C,$0F,$11,$14
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.byte $16,$18,$1A,$1C,$1D,$1E,$1F,$1F
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.byte $20
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sinetable=$6000
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