55 lines
842 B
ArmAsm
55 lines
842 B
ArmAsm
;=================================
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; fakes sines based on parabolas
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; based on code by White Flame via Cruzer/Camelot
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; from codebase64
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;=================================
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; makes 256 entries, min 0 max 127
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; call with X=0!
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;DELTA = $2000
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;VALUE = $2002
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initSineTable:
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ldy #$3f
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; ldx #$00
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; Accumulate the delta (16-bit addition)
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init_sine_loop:
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value_l_smc:
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lda #0
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clc
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adc DELTA
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sta value_l_smc+1
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value_h_smc:
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lda #0
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adc DELTA+1
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sta value_h_smc+1
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; Reflect the value around for a sine wave
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sta sine+$c0,X
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sta sine+$80,Y
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eor #$7f
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sta sine+$40,X
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sta sine+$00,Y
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; Increase the delta, which creates the
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; "acceleration" for a parabola
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lda DELTA
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adc #$08 ; this value adds up to the proper amplitude
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sta DELTA
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bcc init_sine_noflo
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inc DELTA+1
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init_sine_noflo:
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; Loop
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inx
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dey
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bpl init_sine_loop
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; rts
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