rdconfig.asm

一个朋友写的操作系统源码

sseg segment stack

     db 128 dup (0)

sseg ends

dseg segment para public 'global'

     extrn parambuf:byte
     extrn paramnr:word
     configpath db 'config.txt',0  ; file name to be open

dseg ends

cseg segment para public 'code'

     assume cs:cseg,ds:dseg,ss:sseg

     public rdconfig,chksynx

     extrn panic:near

     rdconfig proc near

     push ds  ; save caller's segment
     push es
     push bp  ; make stack frame
     mov bp,sp

     mov ax,3d00h  ; read only open file         
     mov dx,offset configpath
     int 21h
     jnc suc
     ; don't clear carry if error detected
     mov sp,bp
     pop bp  ; restore stack frame
     pop es
     pop ds
     ret     ; leave error code in ax

suc:
     mov bx,ax    ;we will read the config file
     xor ax,ax
     mov ah,3fh
     mov dx,offset parambuf
     mov cx,1024
     int 21h
     jnc suc1
     mov sp,bp
     pop bp
     pop es
     pop ds
     ret
suc1:
     mov [paramnr],ax   ; indicate how many byte we read from config file
     clc                ; guaratee no error

     ; the file handler is already set properly

     mov ah,3eh
     int 21h            ; close config file

     ; we don't care if this operating is successful

     mov sp,bp
     pop bp
     pop es
     pop ds
     ret

     rdconfig endp


     chksynx proc near

     push ds
     push es
     push bp
     mov bp,sp

     sub sp,10

     ; stack arranges like this:
     ; [bp-2]:   the first '/' relative position
     ; [bp-4]:   the first '$' relative position
     ; [bp-6]:   the rest count left after each '/' matched
     ; [bp-8]:   the rest count left after each '$' matched
     ; [bp-10]:  the search time counter

     ; try to find the '#', if '#' not present in our parameter
     ; buf, we will refuse to continue operating and panic, also
     ; we will check the '/','$', we guarantee the each '$' is
     ; behind the each '/', if not, we can't continue operating
     ; and panic syntax error, '/','$' not in group

     cmp word ptr [paramnr],0    ; configuration file can't be NULL
     jne cnext1
     mov ax,105
     push ax
     call panic
cnext1:
     cld                 ; clear direction
     mov di,offset parambuf
     mov cx,[paramnr]
     mov al,35           ; '#'
     repnz scasb         ; find first '#' char
     jz found
     mov ax,100          ; get appropriate error code
     push ax
     call panic
found:

     ; '#' presents, it's time to check the relation
     ; between '/' & '$'

     ; we will initialize the rest count and relative
     ; position for '/' & '$', and create a loop to
     ; check if each '$' is behind each '/'

     mov di,offset parambuf
     mov [bp-2],di       ; '/' position initialize
     mov [bp-4],di       ; '$' position initialize

     mov cx,[paramnr]
     mov [bp-6],cx       ; '/' count initialize
     mov [bp-8],cx       ; '$' count initialize

     mov word ptr [bp-10],0  ; it is the first time

cw1loop:                 ; check loop start here
     cld
     mov di,[bp-4]
     mov cx,[bp-8]
     mov al,36           ; '$'
     repnz scasb         ; find relative first '$' char
     jz cnext2
     cmp word ptr [bp-10],0   ; is it the first time ?
     jz bad1

     ; if we can't find '$' again, we will
     ; guarantee no '/' after that 

     cld
     mov di,[bp-2]
     mov cx,[bp-6]
     mov al,47           ; '/'
     repnz scasb
     jnz match           ; check if in group
     mov ax,108
     push ax
     call panic
match:
     jmp cnext6
bad1:
     mov ax,106
     push ax
     call panic
cnext2:
     mov [bp-4],di       ; set next start of '$'
     mov [bp-8],cx       ; parameter count left of '$'

     cld
     mov di,[bp-2]
     mov cx,[bp-6]
     mov al,47           ; at least one '/' present
     repnz scasb
     jz cnext34
     mov ax,107
     push ax
     call panic

cnext34:

     ; we guarantee at least one '$', one '/' present
     ; also '$' should behind '/'

     cld
     mov di,[bp-2]
     mov cx,[bp-6]
     mov al,47           ; '/'
     repnz scasb         ; find the most close to '$' of '/' char
     jz cnext3

     ; test if next '$' can be found, if so
     ; too bad

     cld
     mov di,[bp-4]
     mov cx,[bp-8]
     mov al,36           ; '$'
     repnz scasb
     jnz toobad

     ; it seems the end of config file
     ; it is not necessary to go on

     jmp cnext6
toobad:
     mov ax,108
     push ax
     call panic
cnext3:

     ; we will check each path if they are all in group
     ; first verify the previous '/' is most close to
     ; '$', if so, restore the search position of '/'
     ; to previous state

     ; be more careful, di is now one
     ; more than that position

     dec di
     mov si,[bp-4]
     dec si
     cmp di,si           ; if exceed the position of '$'
     jb cnext32
     jmp cnext33

     ; not updata the current position of '/'
     ; in effect is to restore the position
     ; to the close previous

cnext32:

     ; remember to restore the di

     inc di
     mov [bp-2],di       ; set next start of '/'
     mov [bp-6],cx       ; parameter count left of '/'
     jmp cnext34         ; get more close to '$'

cnext33:

     ; if all the counts reach zero, it indicates
     ; that the whole syntax check complete without
     ; any error detected, we will move back. if not
     ; then cmp the relative position between '$' & '/'
     ; if '$' > '/', something is wrong with the config
     ; file, it is likely we can't continue again






     cmp word ptr [bp-8],0
     jne cnext4

     ; the '/' can't be found again

     cld
     mov di,[bp-2]
     mov cx,[bp-6]
     mov al,47           ; '/'
     repnz scasb
     jnz cnext35
     mov ax,108
     push ax
     call panic
cnext35:
     jmp cnext6
cnext4:
     inc word ptr [bp-10]
     jmp cw1loop          ; verify next path
cnext5:
     mov ax,108
     push ax
     call panic
cnext6:
     mov sp,bp
     pop bp
     pop es
     pop ds
     ret

     chksynx endp

cseg ends

end