mirror of https://github.com/pret/pokecrystal.git
51 lines
642 B
NASM
Executable File
51 lines
642 B
NASM
Executable File
_Sine:: ; 84d9
|
|
; A simple sine function.
|
|
; Return d * sin(e) in hl.
|
|
|
|
; e is a signed 6-bit value.
|
|
ld a, e
|
|
and %111111
|
|
cp %100000
|
|
jr nc, .negative
|
|
|
|
call .ApplySineWave
|
|
ld a, h
|
|
ret
|
|
|
|
.negative
|
|
and %011111
|
|
call .ApplySineWave
|
|
ld a, h
|
|
xor -1
|
|
inc a
|
|
ret
|
|
|
|
.ApplySineWave: ; 84ef
|
|
ld e, a
|
|
ld a, d
|
|
ld d, 0
|
|
ld hl, .sinewave
|
|
add hl, de
|
|
add hl, de
|
|
ld e, [hl]
|
|
inc hl
|
|
ld d, [hl]
|
|
ld hl, 0
|
|
|
|
; Factor amplitude
|
|
.multiply
|
|
srl a
|
|
jr nc, .even
|
|
add hl, de
|
|
.even
|
|
sla e
|
|
rl d
|
|
and a
|
|
jr nz, .multiply
|
|
ret
|
|
|
|
.sinewave ; 850b
|
|
; A $20-word table representing a sine wave.
|
|
; 90 degrees is index $10 at a base amplitude of $100.
|
|
sine_wave $100
|