Chase H.Q.: Routine at B848

B848: Routine at B848

Used by the routines at main_loop, cpu_driver and escape_scene.
scroll_horizon	B848	LD HL,($A24A)	Return if speed is zero
	B84B	LD A,H
	B84C	OR L
	B84D	RET Z
	B84E	LD A,($A25C)	A = horizon_scroll
	B851	AND A	Set flags
	B852	JR Z,scroll_horizon_3	Jump if zero
	B854	EX AF,AF'	Bank
	B855	RR H	RR H -- shift out carry?
	B857	RLA	A <<= 1
	B858	RLA	A <<= 1
	B859	RLA	A <<= 1
	B85A	AND $06	A &= 6
	B85C	LD C,A	C = A + var_a25d
	B85D	LD A,($A25D)
	B860	ADD A,C
	B861	LD C,A
	B862	LD B,$00	B = 0
	B864	LD HL,$B828	16 word table at table_b828
	B867	ADD HL,BC	HL += BC
	B868	LD B,(HL)	BC = wordat(HL)
	B869	INC HL
	B86A	LD C,(HL)
	B86B	LD HL,$A25E	HL = &var_a25e
	B86E	DEC (HL)	*HL--
	B86F	JR NZ,scroll_horizon_3	Jump if non-zero
	B871	LD (HL),B	*HL = B
	B872	EX AF,AF'	Bank
	B873	LD A,C	A = C
	B874	JP P,scroll_horizon_0	Jump if positive
	B877	NEG	A = -A
scroll_horizon_0	B879	LD HL,$C7E8	Address of operand in 'LD A,x' @ C7E7
	B87C	ADD A,(HL)	A += *HL
	B87D	JP P,scroll_horizon_1	Jump if positive
	B880	ADD A,$14	A += 20
scroll_horizon_1	B882	CP $14	Jump if A < 20
	B884	JR C,scroll_horizon_2	Jump if A < 20
	B886	SUB $14	A -= 20
scroll_horizon_2	B888	LD (HL),A	*HL = A
scroll_horizon_3	B889	XOR A	A = 0
	B88A	LD B,A	B = 0
	B88B	LD E,A	E = 0
	B88C	EX AF,AF'	Bank
	B88D	LD A,($A258)	Return if var_a258 is zero
	B890	OR A
	B891	RET Z
	B892	JP P,scroll_horizon_4	Jump if positive
	B895	INC E	E = -(E + 1)
	B896	NEG	E = -(E + 1)
scroll_horizon_4	B898	LD HL,$B827	32-byte table at table_b828
	B89B	LD C,A	C = A
	B89C	ADD HL,BC	HL += BC
	B89D	LD A,($A25B)	C = var_a25b
	B8A0	LD C,A	C = var_a25b
	B8A1	LD A,($A23F)	A = fast_counter - C
	B8A4	SUB C	A = fast_counter - C
	B8A5	AND A	Set flags
	B8A6	RET Z	Return if non-zero
	B8A7	LD C,(HL)	C = *HL
scroll_horizon_5	B8A8	SUB C	A -= C
	B8A9	JR C,scroll_horizon_6	Jump if carry
	B8AB	INC B	B++
	B8AC	EX AF,AF'	Bank
	B8AD	ADD A,C	A += C
	B8AE	EX AF,AF'	Bank
	B8AF	JR scroll_horizon_5	Jump
scroll_horizon_6	B8B1	LD A,B	A = B
	B8B2	AND A	Set flags
	B8B3	RET Z	Return if zero
	B8B4	LD HL,$A25A	HL = &var_a25a
	B8B7	ADD A,(HL)	A += *HL
	B8B8	LD (HL),A	*HL = A
	B8B9	LD A,B	A = B
	B8BA	RR E
	B8BC	LD B,$00	B = 0
	B8BE	JR NC,scroll_horizon_7	Jump if no carry
	B8C0	DEC B	B--
	B8C1	NEG	A = -A
scroll_horizon_7	B8C3	LD HL,($A171)	HL = horizon_level
	B8C6	LD C,A	C = A
	B8C7	ADD HL,BC	HL += BC
	B8C8	LD ($A171),HL	write it back
	B8CB	EX AF,AF'	Bank
	B8CC	LD HL,$A25B	var_a25b += A
	B8CF	ADD A,(HL)
	B8D0	LD (HL),A
	B8D1	RET	Return