Chase H.Q.: Routine at CD3A

CD3A: Routine at CD3A

Used by the routines at main_loop, cpu_driver and escape_scene. Point IY at the road buffer height data.
main_loop_10	CD3A	LD IYh,$EE	Set IY high byte to road buffer memory region ($EExx)
	CD3D	LD A,($A240)	Load road_buffer_offset into A
	CD40	ADD A,$20	Add 32 so it's the height data offset
	CD42	LD IYl,A	IY is now the road buffer height data pointer
	CD44	LD C,(IY+$00)	Read a height byte into C
	CD47	LD A,($A23F)	A = fast_counter & $E0 -- top three bits
	CD4A	AND $E0	A = fast_counter & $E0 -- top three bits
	CD4C	LD L,A	L = A
	CD4D	LD B,A	B = A
Reduces A by 31.25% ... unsure why that figure.
	CD4E	RRC L	Divide A by 4 and subtract
	CD50	RRC L
	CD52	SUB L
	CD53	RRC L	Divide A by 16 and subtract
	CD55	RRC L
	CD57	SUB L
	CD58	LD L,A	HL = $E600 \| (A + 1)
	CD59	INC L
	CD5A	LD H,$E6
	CD5C	LD A,B	A = B multiplicand
	CD5D	CALL multiply	Call multiply (A = multiplier, C = multiplicand)
	CD60	NEG	A = -A
	CD62	LD C,A	C = A
	CD63	EXX	Bank
This builds the table at $E301.
	CD64	LD B,$15	B = $15
	CD66	LD DE,$E301	DE = $E301
ml10_loop	CD69	EXX	Unbank
	CD6A	LD E,(HL)	E = *HL << 1
	CD6B	SLA E	E = *HL << 1
	CD6D	PUSH HL	Preserve HL
	CD6E	LD D,$00	D = 0
	CD70	LD L,D	L = 0
	CD71	LD H,L	H = 0
	CD72	LD A,C	A = C C is multiply result from above
	CD73	ADD A,(IY+$00)	A += *IY height byte
	CD76	LD C,A	C = A
	CD77	JR Z,ml10_continue
	CD79	JP P,main_loop_10_0
	CD7C	LD A,E	A = E
	CD7D	DEC D	E--
	CD7E	NEG	A = -A
	CD80	LD E,A	E = A
	CD81	LD A,C	A = C
	CD82	NEG	A = -A
main_loop_10_0	CD84	ADD A,A	A <<= 2
	CD85	ADD A,A	A <<= 2
	CD86	JR NC,main_loop_10_1
	CD88	LD L,E	HL = DE
	CD89	LD H,D	HL = DE
	CD8A	ADD HL,HL	HL *= 2
main_loop_10_1	CD8B	ADD A,A	A <<= 1
	CD8C	JR NC,main_loop_10_2
	CD8E	ADD HL,DE	HL += DE
main_loop_10_2	CD8F	ADD HL,HL	HL <<= 1
	CD90	ADD A,A	A <<= 1
	CD91	JR NC,main_loop_10_3
	CD93	ADD HL,DE	HL += DE
main_loop_10_3	CD94	ADD HL,HL	HL <<= 1
	CD95	ADD A,A	A <<= 1
	CD96	JR NC,main_loop_10_4
	CD98	ADD HL,DE	HL += DE
main_loop_10_4	CD99	ADD HL,HL	HL <<= 1
	CD9A	ADD A,A	A <<= 1
	CD9B	JR NC,main_loop_10_5
	CD9D	ADD HL,DE	HL += DE
main_loop_10_5	CD9E	ADD HL,HL	HL <<= 1
	CD9F	ADD A,A	A <<= 1
	CDA0	JR NC,main_loop_10_6
	CDA2	ADD HL,DE	HL += DE
main_loop_10_6	CDA3	ADD HL,HL	HL <<= 1
	CDA4	ADD A,A	A <<= 1
	CDA5	JR NC,main_loop_10_7
	CDA7	ADD HL,DE	HL += DE
main_loop_10_7	CDA8	ADD HL,HL	HL <<= 1
	CDA9	LD A,H	A = H
ml10_continue	CDAA	POP HL	Restore HL
	CDAB	ADD A,(HL)	A += *HL
	CDAC	INC L	L++
	CDAD	EXX	Bank
	CDAE	LD (DE),A	*DE = A -- writes to the table at $E3xx
	CDAF	INC E	E++
	CDB0	INC IYl	IYl++
	CDB2	DJNZ ml10_loop	Loop to ml10_loop
	CDB4	LD A,$A0	A = $A0
	CDB6	LD (DE),A	*DE = A
	CDB7	LD HL,$E336
	CDBA	LD DE,$E301
	CDBD	LD BC,$1560
ml10_loop2	CDC0	LD A,(DE)	A = *DE
	CDC1	CP C
	CDC2	JP P,main_loop_10_8
	CDC5	LD C,A	C = A
main_loop_10_8	CDC6	LD (HL),C	*HL = C
	CDC7	INC L	L++
	CDC8	INC E	E++
	CDC9	DJNZ ml10_loop2	Loop ml10_loop2 while B
	CDCB	LD A,C	C = (C + 3) & $F8
	CDCC	ADD A,$03
	CDCE	AND $F8
	CDD0	LD C,A
	CDD1	SUB (HL)	A -= *HL
	CDD2	LD (HL),C	*HL = C
	CDD3	INC L	L++
	CDD4	LD (HL),A	*HL = A
	CDD5	RET	Return