;EXTRACT.A86 - Trim a file down to a specified size dos equ 21h esc equ 1bh stdout equ 1 ;standard output ; errchk macro call #1 #em ; print macro call >m1 ;skip text db 'EXTRACT --',#1,13,10,'$' m1: pop dx ;get pointer to text mov ah,9 ;write to STDOUT int dos ;... #em ; jmp start argc dw 0 ;storage for argument count argv dw 8 dup (0) ;storage for args, 4 expected newstart dd 0 ;offset where we want the file to start newlength dd 0 ;desired length of output file ihandle dw 0 ;storage for input file handle ohandle dw 0 ;storage for output file handle count dw 0 ;for keeping track of CRLFs crlf db 13,10 ;carriage return/linefeed every 76 chars space equ ' ' ;space character hextbl db 0,1,2,3,4,5,6,7,8,9,-1,-1,-1,-1,-1,-1 db -1,10,11,12,13,14,15,-1,-2,-1,-1,-1,-1,-1,-1,-1 db 16 dup (-1) db -1,10,11,12,13,14,15,-1,-2,-1,-1,-1,-1,-1,-1,-1 db 16 dup (-1) radix10: dd 1,10,100,1000,10000,100000,1000000,10000000,100000000,-1 radix16: dd 1,10h,100h,1000h,10000h,100000h,1000000h,10000000h,-1 start: mov bx,80h ;point to command line length xor cx,cx ;clear the register mov cl,[bx] ;get the length cmp cx,8 ;must be at least 8 chars to be valid arg errchk >e1 ;quit if not add bx,cx ;point to the end inc bx ;now it does mov byte[bx],space ;replace CR with space mov dx,bx ;copy the end pointer xor bx,bx ;make pointer into ARGV array mov di,82h ;point DI to start of command line l1: mov si,di ;copy the pointer mov al,space ;search for space repnz scasb ;look for the first space sub di,si ;get the length dec di ;... mov argv[bx],di ;store it add di,si ;restore the value except for DEC cmp dx,di ;past the end? errchk >e1 ;error if so mov byte [di],0 ;null-terminate the string inc di ;now back where we were add bx,2 ;update the pointer mov argv[bx],si ;save pointer to start of this arg add bx,2 ;update the pointer again inc argc ;update the arg count cmp argc,4 ;done? jne l1 ;loop back if not ;now try to open the input and output files mov dx,argv+2 ;get pointer to first arg mov ax,3d00h ;find matching entry int dos ;try... errchk >e3 ;quit on error mov ihandle,ax ;save the handle if OK mov dx,argv+14 ;point to 4th arg, the output filespec mov ah,3ch ;create the file, overwriting if it exists xor cx,cx ;no attributes int dos ;do it... errchk >e3 ;quit on error mov ohandle,ax ;save the handle ;both files opened OK, try and read the offsets specified mov ax,offset newstart mov bx,word argv+6 ;get pointer to 2nd arg add bx,word argv+4 ;add length dec bx ;less one points to final char call atoi ;convert to binary mov ax,offset newlength mov bx,word argv+10 ;get pointer to 3rd arg add bx,word argv+8 ;add length dec bx ;less one points to final char call atoi ;convert to binary ;all args parsed, now position file pointer where user wants it mov ax,4200h ;move file pointer relative to start of file mov dx,word newstart ;get low word of offset mov cx,word newstart+2 ;high word of offset mov bx,ihandle ;get input handle int dos ;try it errchk >e4 ;quit on failure mov cx,word newlength ;get new length mov ax, word newlength+2 ;make sure it's within bounds or ax,ax ;checking... errchk >e5 ;quit if anything in high word mov ah,3fh ;service requested mov dx,offset buffer ;point to empty space int dos ;perform the read errchk >e6 ;quit on error mov cx,ax ;don't quibble about size, use what we got mov ah,40h ;set up for write mov bx,ohandle ;get output file handle int dos ;do it... errchk >e7 ;quit on error mov ax,4c00 ;else exit normally int dos e1: jc help ;quit on bad command line ret ;else return help: print 'Usage: EXTRACT infile.ext start length outfile.ext' print 'Specify start and length as decimal (12345)' print 'Or hex (c000h). Maximum length is 65535 (ffffh).' mov ax,4c16h ;set errorlevel int dos e3: jnc ret ;return if opened OK print 'Failed on FILE OPEN' mov ax,4c15h ;set errorlevel int dos ret ;target for j?? ret e4: jnc ret ;return if OK print 'Failed to move the read pointer' mov ax,4c14h ;set errorlevel int dos ret ;target for j?? ret e5: jz ret ;return if high word empty print 'Sorry, this can only extract 65,535 bytes maximum' mov ax,4c13h ;set errorlevel int dos ;quit ret e6: jnc ret ;return if OK print 'Failed to read from input file' mov ax,4c12h ;set errorlevel int dos ;quit ret ;target for j?? ret e7: jnc ret ;return if no write error print 'Failed to write out the data' mov ax,4c10h ;set errorlevel int dos atoi: push ax ;address of doubleword result xor ax,ax ;now clear it std ;move backwards mov si,bx ;store address of final char of numeric string mov di,offset radix16 ;assume hex until proven otherwise mov bx,offset hextbl ;get translation table lodsb ;get a byte and update pointer sub al,'0' ;reduce ASCII digit to binary errchk >e2 ;error if control character xlat ;make sure hex digit is converted to binary cmp al,-2 ;was it an "h"? errchk >e3 ;go sort it out jz >a2 ;if so, process as hex ;otherwise process as decimal mov di,offset radix10 ;point to table of base 10 values jmp short >a2 ;skip the digit-processing this first time a1: lodsb ;get a byte and update the pointer or al,al ;zero marks done errchk >e1 ;check... sub al,'0' ;if we returned, binarize it mov bx,offset hextbl ;get translation table address xlat ;translate any hex digits to binary or al,al ;see if invalid (will not catch hex digit if decimal) errchk >e5 ;test, return if OK a2: or al,al ;see if anything left to do jl a1 ;loop if 'h' specifier jnz >a3 ;continue if nonzero add di,4 ;else advance to next doubleword in table jmp short a1 ;loop back around a3: pop bx ;get pointer to result doubleword push bx ;save it on the stack again mov dx,word [di] ;get low word of current value add [bx],dx ;update the result adc word [bx+2],0 ;catch any carry mov dx,[di+2] ;get high word of current value add [bx+2],dx ;update the result errchk >e4 ;carry is an error here dec al ;if we returned, loop around... jmp short a2 ;... e1: ;test for done (null byte) jne ret ;return if not pop ax ;otherwise clean up the stack pop ax ;... cld ;set direction flag back to normal ret ;then return e2: ;test for control character jnc ret ;return if not cld ;direction back to normal print 'Invalid character in numeric argument' mov ax,4c01 ;specify errorlevel int dos ;exit e3: ;test for 'h' indicating hexadecimal; h=-2, invalid=-1 jbe ret ;if 'h', Z was set. If zero or positive, C was set. cld ;direction back to normal print 'Must specify number as decimal, or hex with trailing "h"' mov ax,4c02 ;specify errorlevel int dos ;exit ret e4: ;carry set here means the number was too damn large jnc ret ;return if OK cld ;direction back to normal print 'Numeric argument out of range' mov ax,4c03 ;specify errorlevel int dos e5: ;sign flag set here if invalid jns ret ;return if OK cld ;direction back to normal print 'Non-numeric character in offset specification' mov ax,4c04 ;specify errorlevel int dos ;exit ret ;target for j?? ret buffer: end