; LBA = index of data segment on disk
; CHS = cylinder, header, sector
; T = LBA/sectors per track
; S = (LBA%sectors per track) + 1
; H = T % heads
; C = T / headers
; input, LBA index: ax
; ouput:
; sector number: cl
; cylinder: ch
; head: dh
; Example where LBA = 50h (CHS = 2,0,9)
; ax = 0050h, push this to the stack
; dx = 0000h
; dx = 50h % 12h = 0008h
; ax = 50h / 12h = 0004h
; dx = 0009h
; cx = 0009h
; dx = 0000h
; dx = 04h % 02h = 0000h
; ax = 04h / 02h = 0002h
; dh = 00h (dx = 0000h)
; ch = 02h (cx = 0209h)
; ah = 00h (ax = 0002h)
; cl = 09h OR 00h = 09h (cx = 0209h)
; ax = 0050h
; dl = 50h (dx = 0050h)
; ax = 0050h
; thus:
; cylinder (ch) = 02h
; head (cl) = 00h
; sector (dh) = 09h
math_lba_to_chs:
    push ax
    push dx

    xor dx,dx ; clear dx
    div word [bdb_sectors_per_track] ; (LBA % sectors per track) + 1 = sector
    inc dx  ; sector, dx stores the remainder so we increment that.
    mov cx,dx

    xor dx,dx ; clear dx
    div word [bdb_number_of_heads]
    mov dh,dl ; head, dx stores remainder so we move that up 8 bits to dh

    mov ch,al
    shl ah, 6   ; * 32
    or cl, ah   ; cylinder

    pop ax
    mov dl,al
    pop ax

    ret