Add player inventory and item add routine

src/player.s

@@ -5,13 +5,15 @@ INCLUDE "util.inc"
 
 Section "Player Data", WRAM0
 
-; player data
+DEF PLAYER_INV_SIZE EQU 32
+
 PLAYER_X:: db
 PLAYER_Y:: dw
 PLAYER_DIR:: db
 
 PLAYER_STATE:: db
 PLAYER_VY:: dw
+PLAYER_INV:: DS (2 * PLAYER_INV_SIZE)
 
 Section "Player Code", ROM0
 
@@ -36,7 +38,7 @@ Player_Init::
     ; Clear player data (X/Y initialized by map engine)
     ld hl, PLAYER_DIR
     xor a
-    REPT 7
+    REPT (7 + 2 * PLAYER_INV_SIZE)
         ld [hl+], a
     ENDR
 
@@ -322,3 +324,34 @@ Player_UpdateOAM::
 
 .done:
     ret
+
+; Add item(s) to the player's inventory
+; @param b Item ID
+; @param c Item quantity
+Player_AddInvItem::
+    push de
+
+    ld hl, PLAYER_INV
+    ld e, PLAYER_INV_SIZE
+
+.find_inv_slot:
+    ld a, [hl]
+    cp b
+    jr z, .update_item
+
+    inc hl
+    dec e
+    jr nz, .find_inv_slot
+
+.update_item:
+    ; set item id
+    ld a, b
+    ld [hl+], a
+
+    ; update item qty
+    ld a, [hl]
+    add c
+    ld [hl], a
+
+    pop de
+    ret