source: xtideuniversalbios/trunk/Assembly_Library/Src/Util/Size.asm @ 141

; Project name  :   Assembly Library
; Description   :   Functions for size calculations.

struc BYTE_MULTIPLES
    .B          resb    1
    .kiB        resb    1
    .MiB        resb    1
    .GiB        resb    1
    .TiB        resb    1
endstruc

; Section containing code
SECTION .text

;--------------------------------------------------------------------
; Size_GetSizeToAXAndCharToDLfromBXDXAXwithMagnitudeInCX
;   Parameters:
;       BX:DX:AX:   Size in magnitude
;       CX:         Magnitude in BYTE_MULTIPLES
;   Returns:
;       AX:         Size in magnitude
;       CX:         Tenths
;       DL:         Magnitude character:
;                       'k' = *1024   B = kiB
;                       'M' = *1024 kiB = MiB
;                       'G' = *1024 MiB = GiB
;                       'T' = *1024 GiB = TiB
;                       'P' = *1024 TiB = PiB
;   Corrupts registers:
;       BX, DH
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
Size_GetSizeToAXAndCharToDLfromBXDXAXwithMagnitudeInCX:
    push    si

ALIGN JUMP_ALIGN
.MagnitudeConversionLoop:
    ePUSH_T si, .MagnitudeConversionLoop
    test    bx, bx                  ; Bits 32...47 in use?
    jnz     SHORT Size_DivideSizeInBXDXAXby1024andIncrementMagnitudeInCX
    test    dx, dx                  ; Bits 16...31 in use?
    jnz     SHORT Size_DivideSizeInBXDXAXby1024andIncrementMagnitudeInCX
    cmp     ax, 10000               ; 5 digits needed?
    jae     SHORT Size_DivideSizeInBXDXAXby1024andIncrementMagnitudeInCX
    add     sp, BYTE 2              ; Clean return address from stack
    xchg    si, cx                  ; CX = Remainder (0...1023), SI = Magnitude

    ; Convert remainder to tenths
    xchg    bx, ax                  ; Store AX
    mov     ax, 10
    mul     cx                      ; DX:AX = remainder * 10
    eSHR_IM ax, 10                  ; Divide AX by 1024
    xchg    cx, ax                  ; CX = tenths
    xchg    ax, bx

    ; Convert magnitude to character
    mov     dl, [cs:si+.rgbMagnitudeToChar]

    pop     si
    ret
.rgbMagnitudeToChar:    db  " kMGTP"


;--------------------------------------------------------------------
; Size_DivideSizeInBXDXAXby1024andIncrementMagnitudeInCX
;   Parameters:
;       BX:DX:AX:   Size
;       CX:         Magnitude in BYTE_MULTIPLES
;   Returns:
;       BX:DX:AX:   Size in magnitude
;       SI:         Remainder (0...1023)
;       CX:         Magnitude in BYTE_MULTIPLES
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
Size_DivideSizeInBXDXAXby1024andIncrementMagnitudeInCX:
    push    cx
    xor     si, si                  ; Zero remainder
    mov     cl, 10                  ; Divide by 1024
ALIGN JUMP_ALIGN
.ShiftLoop:
    call    Size_DivideBXDXAXbyTwo
    rcr     si, 1                   ; Update remainder
    loop    .ShiftLoop
    eSHR_IM si, 6                   ; Remainder to SI beginning
    pop     cx
    inc     cx                      ; Increment magnitude
    ret


;--------------------------------------------------------------------
; Size_ConvertSectorCountInBXDXAXtoKiB
; Size_DivideBXDXAXbyTwo
;   Parameters:
;       BX:DX:AX:   Total sector count
;   Returns:
;       BX:DX:AX:   Total size in kiB
;       CF:         Remainder from division
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
Size_ConvertSectorCountInBXDXAXtoKiB:
Size_DivideBXDXAXbyTwo:
    shr     bx, 1                   ; Divide sector count by 2...
    rcr     dx, 1                   ; ...to get disk size in...
    rcr     ax, 1                   ; ...kiB
    ret