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https://github.com/deater/dos33fsprogs.git
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67 lines
1.2 KiB
ArmAsm
67 lines
1.2 KiB
ArmAsm
; fast plot
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; roughly $4D (77) cycles
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; note: ROM plot routine takes $5D (93) cycles
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; original, with SMC code = 77 cycles
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; using indirect-Y/GBASL = 69 cycles
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; split gr_offsets table = 61 cycles
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; color in COLOR
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; horiz=y, vert=A (A trashed, XY Saved)
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fast_plot:
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stx TEMPX ; 3
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lsr ; get low bit in carry ; 2
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tax ; 2
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lda gr_offsets_l,X ; 4+
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sta GBASL ; 3
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lda gr_offsets_h,X ; 4+
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sta GBASH ; 3
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;===
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; 21
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lda COLOR ; 3
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bcs plot_top ; 2/3t
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plot_bottom:
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and #$0f ; 3
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sta TEMP ; 3
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lda #$f0 ; 2
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and (GBASL),Y ; 5
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jmp plot_common ; 3
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plot_top:
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and #$f0 ; 3
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sta TEMP ; 3
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lda #$0f ; 2
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and (GBASL),Y ; 5
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plot_common:
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ora TEMP ; 3
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sta (GBASL),Y ; 6
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;====
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; 31
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ldx TEMPX ; 3
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rts ; 6
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;====
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; 9
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;.align $100
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gr_offsets:
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gr_offsets_l:
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.byte $00,$80,$00,$80,$00,$80,$00,$80
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.byte $28,$a8,$28,$a8,$28,$a8,$28,$a8
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.byte $50,$d0,$50,$d0,$50,$d0,$50,$d0
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gr_offsets_h:
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.byte $4,$4,$5,$5,$6,$6,$7,$7
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.byte $4,$4,$5,$5,$6,$6,$7,$7
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.byte $4,$4,$5,$5,$6,$6,$7,$7
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gr_offsets_end:
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;.assert >gr_offsets = >gr_offsets_end, error, "gr_offsets crosses page"
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