dw global_arena_start: 0x30000
dw global_arena_current: 0x30000
dw global_arena_end: 0x40000

arena_alloc:
    // Just like bump allocator
    push bpr
    mov spr, bpr

    ldw bpr, rg0, 8           // size argument
    ldw global_arena_current, rg1

    add rg1, rg0, rg2         // new_current = current + size
    ldw global_arena_end, rg3

    cmp rg2, rg3
    jgt out_of_memory

    stw rg2, global_arena_current
    mov rg1, acc              // return old current
    stw acc, bpr, 8

    mov bpr, spr
    pop bpr
    return

arena_reset:
    // Reset to start
    push bpr
    mov spr, bpr

    ldw global_arena_start, rg0
    stw rg0, global_arena_current

    mov bpr, spr
    pop bpr
    return