Problem generating a unique password

[Trope]

I am trying to accomplish a simple task (in theory):

1. Get the computer name

2. Loop through each letter performing this operation:

     A. Ascii of letter MOD 10
     B. Divide by 2
     C. Send result to a buffer to hold the final password

so far I have this, and errors seem to be everywhere. Be gentle... :)  I am still new!

Code Select Expand



Am I even close????????


CalculateCombo PROC USES EBX ECX EDX ESI

    LOCAL iComputerNameLen
    LOCAL iSerialLength
    LOCAL sCorrectPassword
   
    xor ecx,ecx                                 ; Clear Registers
    xor eax,eax
    xor ebx,ebx
   
    invoke lstrlen,addr ComputerName            ; Length of ComputerName
    mov iComputerNameLen, eax
   
    mov edi,offset ComputerName                 ; Move Name to EDI

    mov ecx, 0                                  ; Zero out ECX to be sure
   
    .while ecx < iComputerNameLen

            mov dl,byte ptr [edi+ecx]           ; ComputerName Byte
           
            push al                             ; Preserve Registers??
            push ah
           
            mov ax, dl                          ; Character to dl
            div 10h                             ; Divide by 10h

            ; Remainder is in AH
            mov ax, ah
            div 2

            ; Quotient is in AL
            mov al, byte ptr [sCorrectPassword+ecx]
            inc ecx
           
    .endw



CalculateCombo EndP





[dsouza123]

Is it mod 10 decimal or 10 hex (16 decimal) ?

After div 2 what will you add to put it back in regular keyboard character range,
32, 48, 64, 96 ?

Where is the newly generated string stored ?

Usually a push is a 32 bit value  ie  push eax.

For each push a pop is needed to balance the stack.

edi is used but isn't listed in USES

a convention is ebx esi edi are preserved.

[tenkey]

ENDP does not generate a RET instruction.

Add RET.

[hutch--]

Giovanni,

> CalculateCombo PROC USES EBX ECX EDX ESI

Something worth getting right is which registers you preserve and which ones you can trash. You would not normally preserve ECX and EDX as they are transient registers where you normally preserve EBX ESI and EDI. When you use a normal stack frame ESP and EBP are already preserved.

I am a dinosaur and prefer the manual register style of preservation so I would start the proc like this,

Code Select Expand


CalculateCombo proc

    push ebx
    push esi
    push edi

  ; write your prcedure here

    pop edi
    pop esi
    pop ebx

    ret

CalculateCombo endp


With this normal layout you can trash EAX ECX and EDX without having to preserve them but if you use any of EBX ESI and EDI you must preserve them.