snes: use Y*4 in many cases instead of Y

this in theory trades off lots of shifting for a few increments
it does make the code a bit more confusing

tb1_snes/checksum.inc

@@ -1,2 +1,2 @@
-	.word	$f93f		; Complement of checksum
-	.word	$6c0		; Unsigned 16-bit sum of ROM
+	.word	$e1c		; Complement of checksum
+	.word	$f1e3		; Unsigned 16-bit sum of ROM

tb1_snes/level_1.s

@@ -423,22 +423,14 @@ level1_setup_video:
 
 do_new_game:
 
-	;; set up struct pointers
-
-;	ldx	#.LOWORD(missile_0)	; setup missle struct pointer
-;	stx	MISSILE_PL
-
-;	ldx	#.LOWORD(enemy_0)	; setup enemy struct pointer
-;	stx	ENEMY_PL
-
 	;; Clear BSS
 
-	ldx	#$0
-clear_bss:
-	stz	start_bss,X
-	inx
-	cpx	#end_bss-start_bss
-	bne	clear_bss
+;	ldx	#$0
+;clear_bss:
+;	stz	start_bss,X
+;	inx
+;	cpx	#end_bss-start_bss
+;	bne	clear_bss
 
 	;; Init one-time vars
 
@@ -450,7 +442,7 @@ clear_bss:
 ;	jsr	update_shields
 
 	lda	#104
-	sta	shipx			; shipx at start is 18
+	sta	shipx			; shipx at start is 104
 
 	lda	#$1
 	sta	LEVEL			; start at level 1
@@ -581,13 +573,16 @@ same_enemy_type:
 
 	; find empty enemy slot
 
-	ldy	#$20			; point to enemies[0]
+	ldy	#$80			; point to enemies[0] $20 * 4
 find_empty_enemy:
 	jsr	is_sprite_active
 	bcc	add_enemy
 
 	iny
-	cpy	#($20+NUM_ENEMIES)
+	iny
+	iny
+	iny
+	cpy	#($80+4*NUM_ENEMIES)
 	bne	find_empty_enemy
 
 	jmp	move_enemies		; no empty, slots, move on
@@ -803,17 +798,17 @@ store_enemy_kind:
 
 				; want to store to $200 + (Y*4)
 
-	rep	#$20		; set A to 16-bit
-.a16
+;	rep	#$20		; set A to 16-bit
+;.a16
 
-	tya			; copy Y to A
-	asl
-	asl			; multiply by 4
-	tax			; put in X
+	tyx			; copy Y to A
+;	asl
+;	asl			; multiply by 4
+;	tax			; put in X
 
 
-	sep	#$20		; set A back to 8-bit
-.a8
+;	sep	#$20		; set A back to 8-bit
+;.a8
 
 	; determine enemy _x
 	; if < 0, make random between 2->34
@@ -1809,22 +1804,22 @@ done_with_boss:
 	; Missiles are 8,9,10,11 in sprite table
 
 
-	ldy	#$8			; point to missile[0]
+	ldy	#$20			; point to missile[0] (8*4)
 move_missiles:
 	jsr	is_sprite_active
 	bcc	loop_move_missiles	; if not active, skip
 
-	phy
-	tya
-	asl
-	asl
-	tay
+;	phy
+;	tya
+;	asl
+;	asl
+;	tay
 
 	lda	$0201,Y
 	dea
 	sta	$0201,Y
 
-	ply
+;	ply
 
 	cmp	#200
 
@@ -1897,7 +1892,10 @@ done_missile_collision:
 
 loop_move_missiles:
 	iny
-	cpy	#(8+NUM_MISSILES)	; have we checked all missiles?
+	iny
+	iny
+	iny
+	cpy	#($20+4*NUM_MISSILES)	; have we checked all missiles?
 	bne	move_missiles		; if not, loop
 
 done_move_missiles:
@@ -1948,16 +1946,16 @@ key_A:
 	bit	#$80
 	beq	game_unknown
 
-	ldy	#$8			; point to missile[y]
+	ldy	#$20			; point to missile[y] (8*4)
 fire_missiles:
 	jsr	is_sprite_active
 	bcs	end_fire_loop		; if active, skip to next
 
-	phy
-	tya
-	asl
-	asl
-	tay
+;	phy
+;	tya
+;	asl
+;	asl
+;	tay
 
 	lda	#8
 	clc
@@ -1968,15 +1966,18 @@ fire_missiles:
 	sta	$0201,Y
 
 
-	ply
+;	ply
 	jsr	activate_sprite
 
 	bra	done_fire_missiles	; done firing missile
 
 end_fire_loop:
 	iny				; point to next missile
+	iny
+	iny
+	iny
 
-	cpy	#(8+NUM_MISSILES)	; see if we have more missiles
+	cpy	#($20+4*NUM_MISSILES)	; see if we have more missiles
 	bne	fire_missiles		; if so, loop
 
 done_fire_missiles:

tb1_snes/svmwgraph.s

@@ -272,32 +272,31 @@ found_keypress:
 	plp			; restore status
 	rts
 
-;===========================
-;===========================
-; is_sprite_active
-;===========================
-;===========================
-; assumes high sprite table at $0400
-; sets carry if active
-; clears carry if not
-; sprite number in Y
-is_sprite_active:
 
-	php			; save status
+;===========================
+;===========================
+; get_sprite_mask
+;===========================
+;===========================
+; only meant to be called by the routines below
+; sprite number is Y/4
+get_sprite_mask:
 
 	rep	#$30		; A=16bit X/Y=16bit
 .i16
 .a16
 
 	phx			; save X on stack
-	phy			; save Y on stack
 
-	tyx			; copy Y to X
+;	tyx			; copy Y to X
 
-	; address=$0400 + Y/4
+	; address=$0400 + Y/16
 	tya			; copy Y to A
 
-	lsr			; divide by 4
+	lsr			; divide by 16
+	lsr
+	tax
+	lsr
 	lsr
 	tay			; copy back to Y
 
@@ -309,6 +308,26 @@ is_sprite_active:
 .a8
 	lda	SPRITE_HIGH_LOOKUP,X
 				; get bitmask for X
+	plx
+	rts
+
+;===========================
+;===========================
+; is_sprite_active
+;===========================
+;===========================
+; assumes high sprite table at $0400
+; sets carry if active
+; clears carry if not
+; sprite number is Y/4
+is_sprite_active:
+
+	php			; save status
+	phy			; save Y on stack
+
+	jsr	get_sprite_mask
+.a8
+	; mask is in A
 
 	and	$0400,Y		; sprite on screen when bit is 0
 
@@ -316,14 +335,12 @@ is_sprite_active:
 
 sprite_is_not_active:
 	ply
-	plx
 	plp
 	clc
 	rts
 
 sprite_is_active:
 	ply
-	plx
 	plp
 	sec
 	rts
@@ -335,40 +352,20 @@ sprite_is_active:
 ;===========================
 ;===========================
 ; assumes high sprite table at $0400
-; sets carry if active
-; clears carry if not
-; sprite number in Y
+; sprite number is Y/4
 activate_sprite:
 
 	php				; store status
-	phx				; store X on stack
 	phy				; store Y on stack
 
-	rep	#$20			; make A 16-bit
-.a16
-
-	tyx				; copy Y to X
-
-	; address=$0400 + Y/4
-	tya				; copy Y to A
-	lsr				; divide by 4
-	lsr
-	tay				; transfer back to Y
-
-	txa				; get saved copy of Y
-	and	#$3			; mask to get low bits
-	tax				; transfer back to X
-
-	sep	#$20			; make A 8-bit
+	jsr	get_sprite_mask
 .a8
-	lda	SPRITE_HIGH_LOOKUP,X	; load from lookup table
 	eor	#$ff			; negate it
 
 	and	$0400,Y			; sprite on screen when bit is 0
 	sta	$0400,Y			; store it back out
 
 	ply				; restore values from stack
-	plx
 	plp
 	rts				; return
 
@@ -379,38 +376,18 @@ activate_sprite:
 ;===========================
 ;===========================
 ; assumes high sprite table at $0400
-; sets carry if active
-; clears carry if not
-; sprite number in Y
+; sprite number is Y/4
 deactivate_sprite:
 
 	php					; save status on stack
-	phx					; save X
 	phy					; save Y
 
-	tyx					; copy Y to X
-
-	rep	#$20				; set A to 16-bit
-.a16
-
-	; address=$0400 + Y/4
-	tya					; copy Y to A
-	lsr					; divide by 4
-	lsr
-	tay					; copy back to Y
-
-	txa					; get low bits into X
-	and	#$3				; Mask
-	tax
-
-	sep	#$20				; set A to 8-bit
+	jsr	get_sprite_mask
 .a8
-	lda	SPRITE_HIGH_LOOKUP,X		; lookup bits in table
 
 	ora	$0400,Y			; sprite off screen when bit is 1
 	sta	$0400,Y			; save value back out
 
 	ply				; restore Y
-	plx				; restore X
 	plp				; restore status
 	rts				; return