iexecdos.asm

还是一个词法分析程序

        ; Set flag so we know that a command was given.
        mov     [DosCommandGiven],COMMAND_GIVEN
        clc     ; No error
    @@Exit:
        ret
    endp ParseDosCommand


    dataseg
    ; Local data area for ExecuteDosCommand

    ; The following act as pointers to the data for this invocation of
    ; ExecuteDosCommand.
    DirectoryPath dw ?
    FileNameSeg   dw ?
    FileName      dw ?

    codeseg
    proc ExecuteDosCommand
    ;   This procedure actual executes the DOS command, if given, for
    ;   each file that is found.
    ;
    ;   Input
    ;       ax:si - Offset of filename
    ;       di - offset of currentdir
    ;   Output
    ;       none
    ;   Calling conventions
    ;       NA
    ;   Registers modified
    ;       all except es

        mov     [DirectoryPath],di
        mov     [FileNameSeg],ax
        mov     [FileName],si

        push    es
        cmp     [DosCommandGiven],COMMAND_GIVEN
        jne     @@Exit

        ; Blank out the buffer for the command to do.
        cld     ; Autoincrement
        mov     ax,seg CommandToDo
        mov     es,ax
        mov     di,offset CommandToDo
        mov     cx,COMMAND_BUFFER_LENGTH
        mov     al,0
        rep stosb

        ; We need to go into a loop of copying from the input command
        ; string until we find a %

        mov     di,offset CommandToDo        ; For results            es:di
        xor     cl,cl                        ; Length of output string
        inc     di                           ; Move over the leading length byte

        mov     si,offset StartOfBuff
        call    CopyAsciizString             ; Copy the starting /C

        mov     si,offset DosCommandBuffer   ; For original command   ds:si
        mov     ch,[si]                      ; Length of original string
        inc     si                           ; Move over the leading length byte


    @@ProcessChar:
        or      ch,ch
        jz      SourceExhausted
        lodsb                   ; Load current byte
        dec     ch              ; One less character to get

        cmp     al,'%'
        je      @@ProcessSpecial
    @@EmitChar:
        stosb                   ; This route handles regular characters
        inc     cl              ; Increment length of output string
        cmp     cl,COMMAND_BUFFER_LENGTH-1
        jae     SourceExhausted ; Force early termination if we run out of room!
        jmp     @@ProcessChar

    @@ProcessSpecial:           ; We saw a % sign.
        or      ch,ch
        jz      @@EmitChar      ;Output because there is nothing more after it
        lodsb
        dec     ch
        ; Try to recognize one of the %x directives:
        cmp     al,'1'
        je      Process1
        cmp     al,'2'
        je      Process2
        cmp     al,'3'
        je      Process3
        cmp     al,'4'
        je      Process4
        cmp     al,'5'
        je      Process5

        ; We don't recognize it, so output the %x unchanged.
        mov     [byte es:di],'%'  ; Put out the % that got us here
        inc     cl                ; Increment length of output string
        inc     di
        jmp     @@EmitChar        ; Output the character in AL


    Process1:
        call    EmitPath
        cmp     cl,COMMAND_BUFFER_LENGTH-1
        jae     SourceExhausted ; Force early termination if we run out of room!
    Process2:
        call    EmitFileRoot
        cmp     cl,COMMAND_BUFFER_LENGTH-1
        jae     SourceExhausted ; Force early termination if we run out of room!
        jmp     Process5

    Process3:
        call    EmitPath
        jmp     @@ProcessChar

    Process4:
        call    EmitFileRoot
        call    EmitDot
        jmp     @@ProcessChar

    Process5:
        Call    EmitDot
        call    EmitExtension
        jmp     @@ProcessChar

    SourceExhausted:
        ;We need to fill in the length byte, along with a 13 at the end.
        mov     al,13
        stosb
        mov     [CommandToDo],cl     ; Fill in the length byte

        mov     cx,seg CommandToDo
        mov     dx,offset CommandToDo
        call    DoDosCommand

    @@Exit:
        pop     es
        ret
    endp ExecuteDosCommand



    proc EmitPath
    ; This routine writes the drive and path to the output command.com string

        push    si ds

        mov     si,offset Drive
        call    CopyPascalString

        mov     si,[DirectoryPath]
        cmp     [byte ds:si],'A'
        jl      @@NoBackSlash
        dec     si
    @@NoBackSlash:
        call    CopyAsciizString

        mov     ax,seg SwitchChar
        mov     ds,ax
        mov     si,offset SwitchChar
        call    CopyPascalString

        pop     ds si
        ret
    endp EmitPath



    proc EmitFileRoot
    ; This routine writes the part of the filename that is before the
    ; extension to the output string that will be sent to COMMAND.COM

        push    si ds
        mov     si,[FileName]
        mov     ax,[FileNameSeg]
        mov     ds,ax

        mov     al,'.'
        call    CopyTerminatedString
        pop     ds si
        ret
    endp EmitFileRoot



    proc EmitExtension
    ; This routine writes the extension of the current file to the
    ; output string that will be sent to COMMAND.COM

        push    si ds
        mov     si,[FileName]
        mov     ax,[FileNameSeg]
        mov     ds,ax

        mov     al,'.'
    @@CheckAgain:
        mov     ah,[ds:si]
        cmp     ah,al
        je      @@DotFound
        or      ah,ah
        jz      @@Exit       ; Quit searching if a zero is found
        inc     si
        jmp     @@CheckAgain
    @@DotFound:
        inc     si
        call    CopyAsciizString
    @@Exit:
        pop     ds si
        ret
    endp EmitExtension



    proc EmitDot
    ; This routine outputs a . to the string to be sent to command.com.

        mov     [byte es:di],'.'  ; Put out the .
        inc     cl
        inc     di
        ret
    endp EmitDot


    ; The following string copy routines are special for this module.
    ; DS:SI point to the source string. (DS:SI are preserved.)
    ; ES:DI Point to the destination string area. (ES:DI is not preserved.)
    ; CL is updated for every byte output to ES:DI.

    proc CopyPascalString
    ; Copy pascal type string to ES:DI, but omit the length byte.
        xor     bx,bx
        mov     al,[ds:si]
        add     cl,al

    @@CopyChar:
        mov     ah,[ds:si+1+bx]
        mov     [es:di],ah
        inc     di
        inc     bx
        dec     al
        jnz     @@CopyChar

        ret
    endp CopyPascalString



    proc CopyAsciizString
    ; Copy a string that is terminated by a zero.
        xor     al,al
        call    CopyTerminatedString
        ret
    endp CopyAsciizString



    proc CopyTerminatedString
    ; Copy a string terminated by any character.
    ; al contains character to stop copy. Normally 0 for ASCIIZ strings
    ; Note that the terminator is not copied.
        xor     bx,bx

    @@CopyMoreChar:
        mov     ah,[ds:si+bx]
        cmp     ah,al
        jz      @@AtEnd
        mov     [es:di],ah
        inc     di
        inc     bx
        inc     cl
        jnz     @@CopyMoreChar
    @@AtEnd:
        ret
    endp CopyTerminatedString






segment zzzzzseg   ; Dummy final segment for calculating program size
                   ; to release memory back to DOS.
ends    zzzzzseg

endif   ; ifndef MDL

end