Optimize collision routines

src/collision.s

@@ -1,13 +1,12 @@
 INCLUDE "oam.inc"
 
-SECTION "Collision", ROMX
+SECTION "Collision", ROM0
 
 ; Determines if player has hit the background
 ; @return NZ = false, Z = true
 player_bg_collides::
     ; c = x % 8 == 0 ? x/8 : x/8 + 1
-    ld hl, PLAYER_X
-    ld a, [hl]
+    ld a, [PLAYER_X]
     ld c, a
     and %111
     jr z, .skip_inc_c
@@ -20,8 +19,7 @@ player_bg_collides::
     srl c
 
     ; b = y % 8 == 0 ? y/8 : y/8 + 1
-    inc hl
-    ld a, [hl]
+    ld a, [PLAYER_Y]
     ld b, a
     and %111
     jr z, .skip_inc_b
@@ -58,8 +56,7 @@ player_bg_collides::
 ; @note NZ = false, Z = true
 player_in_air::
     ; c = x % 8 == 0 ? x/8 : x/8 + 1
-    ld hl, PLAYER_X
-    ld a, [hl]
+    ld a, [PLAYER_X]
     ld c, a
     and %111
     jr z, .skip_inc_c
@@ -72,8 +69,7 @@ player_in_air::
     srl c
 
     ; b = y % 8 == 0 ? y/8 : y/8 + 1
-    inc hl
-    ld a, [hl]
+    ld a, [PLAYER_Y]
     ld b, a
     and %111
     jr z, .skip_inc_b
@@ -107,18 +103,14 @@ can_move_to:
     push bc
     push hl
 
-    ; hl = bg_collision_data
-    ld hl, BG_COLLISION_DATA
-    ld d, [hl]
-    inc hl
-    ld e, [hl]
-    push de
+    ld a, [BG_COLLISION_DATA]
+    ld h, a
+    ld a, [BG_COLLISION_DATA + 1]
+    ld l, a
 
-    ; de = map width
-    ld hl, BG_MAP_WIDTH
+    ld a, [BG_MAP_WIDTH]
     ld d, 0
-    ld e, [hl]
-    pop hl
+    ld e, a
 
     ; compute map index (HL + B * (BG_MAP_WIDTH + 1) + C)
 .mul_y_width: