Macro factors out sine code, just like sine data, since it's used 5 times

macros/code.asm

@@ -52,3 +52,50 @@ endc
 endr
 	and x
 ENDM
+
+calc_sine_wave: MACRO
+; input: a = a signed 6-bit value
+; output: a = d * sin(a * pi/32)
+	and %111111
+	cp  %100000
+	jr nc, .negative\@
+	call .apply\@
+	ld a, h
+	ret
+.negative\@
+	and %011111
+	call .apply\@
+	ld a, h
+	xor $ff
+	inc a
+	ret
+.apply\@
+	ld e, a
+	ld a, d
+	ld d, 0
+if _NARG == 1
+	ld hl, \1
+else
+	ld hl, .sinetable\@
+endc
+	add hl, de
+	add hl, de
+	ld e, [hl]
+	inc hl
+	ld d, [hl]
+	ld hl, 0
+.multiply\@ ; factor amplitude
+	srl a
+	jr nc, .even\@
+	add hl, de
+.even\@
+	sla e
+	rl d
+	and a
+	jr nz, .multiply\@
+	ret
+if _NARG == 0
+.sinetable\@
+	sine_table 32
+endc
+ENDM