נושא: מרצים גרועים באת’’ם/צמצום פער

נשלח בתאריך: 29 April 2011 בשעה 16:23 | IP רשוּם

שלום אני סטודנט להנדסת תוכנה תואר ראשון ובמהלך קורס את''מ נתקלתי באטימות מצד המרצים שממהרים עם החומר ולא מסבירים אפילו קצת כמו שצריך. מרצה אחת היא אנטיפטית רצינית, השני מרצה משעמם ולא מובן.

ככה אני לא מבין קטעי קוד מסויימים. אם תוכלו תסבירו לי בבקשה איך הם עובדים תודה!

;
;  stack3.asm - demonstrate hardware stack usage.
;
    .MODEL SMALL
    .STACK 100h
    .DATA
Separator       EQU '#'
DisplayString   DB  64 DUP('$')
Numbs           DB '0123456789'
Stack_Size      DW (?)
     .CODE
ProgStart:
     MOV AX,@DATA                ; Set DS to point ...
     MOV DS,AX                   ; ... to data segment
                                      ;
     MOV DI,OFFSET DisplayString ; Have DI point to start ...
                                     ; ... of DisplayString
     MOV Stack_Size,SP           ; Save stack size
                                    ;
     XOR BX,BX                   ;  BX := 0;
     MOV CX,5                    ;  Size(Numbs) = 2*5
                                     ;
StackStore:
        MOV DX,WORD PTR Numbs[BX]   ; Read two bytes in Numbs
        PUSH DX                   &nb sp;  ; Store in Stack
        MOV [DI],DX                 ; Store in DisplayString
        ADD BX,2                    ; BX point to next word in Numbs
        ADD DI,2                    ; DI point to next available position
      LOOP StackStore               ; Repeat 5 times
                                      ;
     MOV DL,Separator            ;
     MOV [DI],DL                 ; Store '#' ...
     INC DI                   &nb sp;  ;   ... to separate
                                      ;
     MOV CX,Stack_Size           ;
     SUB CX,SP                   ; Set CX to equal ...
                                     ;  .. number of relevant ...
                                     ;  ... bytes in stack
     MOV BP,SP                   ;
StackLoop1:                  & nbsp;       ; Print Stack downward
        MOV BL,[BP]                 ;
        INC BP                   &nb sp;  ;
        MOV [DI],BL                 ; Store in DisplayString
        INC DI                   &nb sp;  ; point to next available position
     LOOP StackLoop1              ;
                                      ;
     MOV DL,Separator            ;
     MOV [DI],DL                 ; Store '#' ...
     INC DI                   &nb sp;  ;   ... to separate
                                      ;
     MOV BX,[BP-3]               ;  Retrieve eighth and ninth bytes ...
     MOV [DI],BX                 ;   ... in stack
     ADD DI,2                    ;
                                      ;
     MOV DL,Separator            ;
     MOV [DI],DL                 ; Store '#' ...
     INC DI                   &nb sp;  ;   ... to seperate
                                      ;
     MOV BP,SP                ;  Retrieve third and forth bytes ...
     MOV BX,[BP+2]               ;   ... in stack
     MOV [DI],BX                 ;
     ADD DI,2                    ;
                                      ;
     MOV DL,Separator            ;
     MOV [DI],DL                 ; Store '#' ...
     INC DI                   &nb sp;  ;   ... to seperate
                                      ;
     MOV CX,Stack_Size           ;
     SUB CX,SP                   ; Set CX to equal ...
                                      ;  ... number of relevant ...
                                      ;  ... bytes in stack
     MOV BP,Stack_Size            ;
     DEC BP                   &nb sp;  ; Set BP to point to last ...
                                      ; ... byte in stack
StackLoop2:                  & nbsp;       ; Print stack, upward
        MOV BL,[BP]                  ;
        DEC BP                   &nb sp;  ;
        MOV [DI],BL                 ; Store in DisplayString
        INC DI                   &nb sp;  ; point to next available position
     LOOP StackLoop2              ;
                                      ;
     MOV AH,9                    ; Set print option for int 21h
     MOV DX,OFFSET DisplayString ;  Set  DS:DX to point to DisplayString
     INT 21h                   &n bsp; ;  Print DisplayString
                                      ;
     MOV AH,4Ch                  ; Set terminate option for int 21h
     INT 21h                   &n bsp; ; Return to DOS (terminate program)
     END  ProgStart

השני:

;
;  procs3.asm - Demonstrate use of local procedures
;
    .MODEL SMALL
    .STACK 100h
    .DATA
Max_Str_Lngth EQU 1000
PromptString DB 'Enter string:',13,10
ResultMsg DB 'The string you entered:',13,10
InputString  DB  Max_Str_Lngth  DUP (?)
InputLength DW ?
                                    ;
     .CODE
Dos_Readln  PROC  FAR
    ; CALL INT 21h with AH = 3Fh, BX = 0
    ; Read from stndin until eoln, ...
    ; ... but no more than CX chars into buffer
    ; Input expected:
    ;    DX = Buffer OFFSET
    ;    CX = Max buffer size
    ; Output:
    ;    AX = Number of chars read.
    ;
     PUSH BX                   &nbs p;   ; Preserve service register
     MOV AH,3Fh                    ; DOS read from handle function #
     MOV BX,0                   &n bsp;  ; Standard input handle
     INT 21h                   &nb sp;   ; Get the string
     POP BX                   &nbs p;    ; Restore service register
     RET
Dos_Readln  ENDP
                                    ;
                                    ;
Dos_Write  PROC  FAR
    ; CALL INT 21h with AH = 40h, BX = 1
    ; Write to stndout CX chars from buffer
    ; Input expected:
    ;    DX = Buffer OFFSET
    ;    CX = Number of chars to print.
    ;
     PUSH AX                   &nbs p;   ; Preserve service register
     PUSH BX                   &nbs p;   ; Preserve service register
     MOV AH,40h                    ; DOS write from handle function #
     MOV BX,1                   &n bsp;  ; Standard output handle
     INT 21h                   &nb sp;   ; Print the string
     POP BX                   &nbs p;    ; Restore service register
     POP AX                   &nbs p;    ; Restore service register
     RET
Dos_Write ENDP
                                    ;
                                    ;
Main:
     MOV AX,@DATA
     MOV DS,AX                   & nbsp; ; Set DS  to point to data segment
                                    ;
     MOV DX,OFFSET PromptString    ; Set DX to point to string
                                    ; Set number of chars to print
     MOV  CX,ResultMsg - PromptString
     CALL Dos_Write                ; Print the string
     MOV CX,Max_Str_Lngth          ; Read up to maximum number of chars
     MOV DX,OFFSET InputString     ; Store the string here
     CALL Dos_Readln               ;
     MOV  InputLength,AX           ; Preserve input length
                                    ;
     MOV DX,OFFSET ResultMsg       ; Set DX to point to string
                                    ; Set number of chars to print
     MOV  CX,InputString - ResultMsg
     CALL Dos_Write                ; Print the string
     MOV DX,OFFSET InputString     ; Set DX to point to string
     MOV  CX,InputLength           ; Set number of chars to print
     CALL Dos_Write                ;
                                    ;
     MOV AH,4Ch                    ; DOS terminate program function #
     INT 21h                   &nb sp;   ; Terminate the program
     END Main