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269 lines
11 KiB
NASM
269 lines
11 KiB
NASM
3 weeks ago
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;GETCD V 1.0 | 3-NOV-2024 Jay Moore/dewdude@pickmy.org
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;Finds CDROM drive letter and places in CDROM
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;environment variable
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;
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;A replacement for FINDCD.EXE written in NASM Assembly and
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;manipulates a lot of memory directly. Not a drop-in
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;replacement, but close. Designed as a .BAT utility, the
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;only user interaction is feeding it a path/filename and
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;checking the environment variable. Default returns first
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;CDROM drive that has a disc.
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;
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;GETCD [/?] SEARCHSTRING
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;
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;SEARCHSTRING can be a file, directory name, path, or wildcard.
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;Not specifying a file does a wildcard search on root of CD.
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;You do not need to add a leading \ to the string.
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;/? displays the usual help, except poorly written.
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;
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;CDROM=E:
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;
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;Is how the variable will be set. If you desire a trailing \;
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;just have your script 'set CDROM=%CDROM%\'
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;
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;This will absolutely overwrite any existing CDROM= contents with
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;the above format; and will also shift data around to make it the
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;exact length. It will also create an environment variable if none
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;exists. This is contrast with FINDCD.EXE; which not only needs
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;you to set the CDROM= variable first, but requires patching the
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;.exe to change the file search. Gross.
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;
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;Displayed output is minimal. The only error displayed is if the
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;environment block is full. A lack of CDROM drives will exit with
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;errorlevel 255. Anything else just doesn't change (or create) the
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;CDROM variable. You'll need to do that after execution in your script.
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;
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;argument section of PSP starts at 80h; byte count, bytes, terminator.
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;term is 0x0D, but it's not included in byte count. this can include
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;spaces if full name.ext is used or user just hit space.
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;the pointer to parent's PSP lives at 16h; env-block pointer is 2Ch
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;offset 3 one segment back is the block allocation size.
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;this means I initialize di to 10h now and just leave es where it is
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;as all counts are relative from di's initialization
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[CPU 8086]
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[BITS 16]
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org 100h
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section .text
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global start
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start:
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xor cx, cx ; clear out cx
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mov si, 80h ; move si to psp argument count
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mov cl, [si] ; load argument byte count
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argproc:
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jcxz varinit ; stop if cx is 0
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inc si ; increment si
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cmp byte [si], 20h ; Invalid char/space check
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jbe skipit ; jump to loop if <20h
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cmp byte [si], 5ch ; is it backslash
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jz skipit ; jump if it is
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cmp word [si], 3f2fh ; check for /?
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jz hllp ; jump if it is
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jmp ldfile ; land here when done
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skipit:
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loop argproc ; dec cx, jmp argproc ;)
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ldfile:
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lea di, filename ; load filename to di
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repe movsb ; copy argument to filename
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mov byte [di], 0 ; null for good measure
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varinit:
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mov es, [16h] ; parent psp pointer
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mov ax, [es:2ch] ; load block segment
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dec ax ; segment one below
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mov es, ax ; go back a segment
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mov ax, [es:3h] ; this is the size
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mov cl, 4 ; load 4 to cl for shl
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shl ax, cl ; bit shift left 4
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mov [blocksize], ax ; store
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mov di, 10h ; move di up to env blk
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readblock:
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cmp word [es:di], 0 ; end of block?
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jz endofblock ; variiable missing
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lea si, envname ; load envname address
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mov cx, 6 ; load six
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repe cmpsb ; repe compare string
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jnz readblock ; if not variable, go back up
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sub di, 6 ; subtract 6
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mov [envstart], di ; write starting location
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add di, 6 ; place it back
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findend:
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inc di ; now to find the end
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cmp word [es:di], 0 ; is it the end?
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jnz findend ; jump back up if not
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endofblock:
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inc di ; actual end of block
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mov [blockend], di ; write that down
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cmp word [envstart], 0 ; did we find a var
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jz noenv ; jump if novar
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mov di, [envstart] ; go back to the env start
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mov ax, 1212h ; get the asciz length
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int 2fh ; in to cx
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cmp cx, 9 ; and see if it's 9
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jb envtoosmall ; jump to envtosmall if too small
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ja envtoobig ; jump to envtoobig if too big
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envokay:
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add di, 6 ; drive letter is six in
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jmp drivego ; es:di ready for letter
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envtoobig:
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mov si, di ; duplicate pointers
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mov word [es:di+7], 0x003A ; write : and null
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add si, 9 ; put si where i need di
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call endcheck ; check relative position
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call bytesize ; get byte count to copy
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xchg di, si ; now we swap
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cld ; clear that direction
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call copybytes ; copy byte routine
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mov word [es:di], 0 ; double null new end
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mov di, [envstart] ; go back to the env
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jmp envokay ; might as well jump
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noenv:
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call envfree ; check free space
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mov di, [blockend] ; go to block end
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newenv:
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lea si, envname ; load address of envname
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mov cx, 8 ; we want 8 bytes
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repe movsb ; write 'em
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mov word [es:di], 0000h ; double null new term
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sub di, 2 ; back di up two
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jmp drivego ; es:di is ready
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envtoosmall:
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mov byte [oneornine], 01h ; change envfree's cmp value
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call envfree ; check environment space
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call endcheck ; check relative position
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call bytesize ; call for byte count
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add cx, 3 ; add three to that count
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mov si, [blockend] ; load the end of block offset to si
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mov di, [blockend] ; load it again to di
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inc di ; move it up one
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std ; set direction flag
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call copybytes ; copybytes routine
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mov word [es:di+1], 0x003A ; write the : and null one byte up
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drivego:
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mov ax, 2524h ; Ignore Critical Errors
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lea dx, [new24] ; pointer to new handler
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int 21h ; interrupt to change ivt
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mov ax, 1500h ; function to get drive info
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int 2Fh ; from int 2f
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xchg bx, cx ; swap count and starting number
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jcxz nodrives ; see if we have drives
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add bl, 41h ; convert number to letter
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loadltr:
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push cx ; push drive count to stack
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mov [drivevar], bl ; copy drive letter to ram
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lea dx, drivevar ; load address of drivevar
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mov ah, 4Eh ; load find first file
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mov cl, 17h ; all the options
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int 21h ; call the interrupt
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jnc envset ; found file, go on
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pop cx ; pop drive count back in to CX
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inc bl ; increment to next drive
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loop loadltr ; loop back around
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jmp exit ; no match, leave
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envset:
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lea si, drivevar ; loads address to si
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movsb ; moves ds:si to es:di
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jmp exit ; we're done, go home
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nodrives:
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mov al, 0FFh ; load errorlevel 255 to al
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exit:
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mov ax, 4c00h ; standard dos kernel terminate
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int 21h ; bye.
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endcheck:
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push cx ; push cx to stack
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add cx, di ; add di to cx
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sub cx, [blockend] ; subtract blockend from cx
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jcxz fakenew ; jump if zero
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pop cx ; invert cx (it should be neg)
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ret ; go back to moving bytes
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fakenew:
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sub sp, 04h ; reset the stack you animal
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mov di, [envstart] ; load di
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jmp newenv ; pretend it's new
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copybytes:
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push ds ; push ds on to the stack
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push es ; push es on to the stack
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pop ds ; pop es in to ds for this
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repe movsb ; copy ds:si to es:di till cx is 0
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pop ds ; pop ds's original value back out
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ret
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envfree:
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mov ax, [blocksize] ; load size
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sub ax, [blockend] ; calculate free
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cmp al, [oneornine] ; need n free
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jz blockfull ; not enough space
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ret ; return if ok
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bytesize:
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add di, cx ; place di at next variable
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mov cx, [blockend] ; load the end of the block
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sub cx, di ; subtract the actual usage
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ret ; return from subroutine
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hllp:
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lea dx, hlptxt ; address of $-terminated strong
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mov ah, 09h ; display string function
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int 21h ; dos interrupt
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jmp exit ; exit
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new24:
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mov al, 3 ; FAIL! (Hitting F, but faster)
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iret ; Return from interrupt.
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section .data
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hlptxt:
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db 'GETCD 1.0 | 4-NOV-2024 | dewdude@pickmy.org | Freeware/MIT', 0x0d, 0x0a
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db 'Sets "CDROM=[driveletter]:" by searching CD-ROM drives', 0x0d, 0x0a
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db 'USAGE: GETCD [/?] [FILE/OR/PATH/TO/FILE.EXT]', 0x0d, 0x0a
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db 'Finds file on CD-ROM drives. Returns first match. Allows wildcards.', 0x0d, 0x0a
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db 'Creates/adjusts variable. Default search is wildcard.$', 0x0d, 0x0a
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blockfull: db 'NO ENV FREE $'
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blocksize: db 0, 0 ; holds block size
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envstart: db 0, 0 ; start of cdrom=
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blockend: db 0, 0 ; end of used block
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oneornine: db 09h ; default 9
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envname: db 'CDROM=' ; variable name
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drivevar: db '0:\' ; variable's variable
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filename: db '*', 0x00 ; (default) filename
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;MIT No Attribution
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;
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;Copyright 2024 Jay Moore
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;
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;Permission is hereby granted, free of charge, to any person obtaining a copy of this
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;software and associated documentation files (the "Software"), to deal in the Software
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;without restriction, including without limitation the rights to use, copy, modify,
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;merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
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;permit persons to whom the Software is furnished to do so.
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;
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;THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
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;INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
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;PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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;HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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;OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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;SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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