name free
page 60,132
title''FREE --- Report free space on disk''
; FREE --- a utility to report free space on
; The default or selected disk drive.
;
; Requires PC-DOS or MS-DOS 2.0.
;
; Used in the form:
; A> FREE [unit:]
; (Item in square brackets is optional)
;
; Version 1.0 July 4, 1984
; Copyright (c) 1984 by Ray Duncan
; May be freely reproduced for non-commercial use.
cr equ 0dh; ASCII carriage return
lf equ 0ah; ASCII line feed
blank equ 20h; ASCII space code
eom equ''$''; end of string marker
; Here we define a dummy segment containing labels
; For the default file control block and the command tail buffer,
; So that the main program can access those locations.
;
psp segment para public''PSP''
org 05ch
fcb label byte; default file control block
org 080h
command label byte; default command buffer
psp ends
cseg segment para public''CODE''
assume cs: cseg, ds: psp, es: data, ss: stack
get_drive proc near; get drive selection, if any,
; Otherwise obtain the identity
; Of the current disk drive.
; Return drive (1 = A, 2 = B, etc) in AL.
;
mov al, fcb; Pick up the drive code, parsed
; By DOS into the default file
; Control block.
or al, al; Is it the default?
jnz get_drive1; no, use it
mov ah, 19h; Yes, get the actual current
int 21h; drive from PC-DOS.
inc al; Increment to match FCB code.
get_drive1:; Return drive code in AL.
ret
get_drive endp
free proc far; entry point from PC-DOS
push ds; save DS: 0000 for final
xor ax, ax; return to PC-DOS
push ax
mov ax, data; make our data segment
mov es, ax; addressable via ES register.
mov ah, 30h; check version of PC-DOS.
int 21h
cmp al, 2
jae free1; proceed, DOS 2.0 or greater.
mov dx, offset msg2; DOS 1.x --- print error message
mov ax, es; and exit. First fix up DS register
mov ds, ax; so error message is addressable.
jmp free4
free1: call get_drive; get drive selection into DL.
push es; copy ES to DS for remainder
pop ds; of the program ...
assume ds: data; and tell assembler about it.
mov dl, al
add al,''A''-1; form drive letter from drive code,
mov outputb, al; and put it into the output string.
mov ah, 36h; now call DOS to get free disk space.
int 21h
cmp ax, -1; was drive invalid?
je free3; yes, go print error message
; Drive was ok, so now registers are ...
; AX = number of sectors per cluster
; BX = available clusters,
; CX = number of bytes per sector,
; DX = total clusters per drive.
; Calculate free space:
mul cx; sectors per cluster backup bin conf config data eshow_sitemap.html generate.sh log maint sitemap.html svn tmp bytes per sector
; (We assume this won''t overflow into DX)
mul bx; then backup bin conf config data eshow_sitemap.html generate.sh log maint sitemap.html svn tmp available clusters
; DX: AX now contains free space in bytes.
; SI = last byte address for converted string.
mov si, offset (outputa +9)
mov cx, 10; CX = 10, radix for conversion
call bin_to_asc; convert free space value to ASCII,
mov dx, offset output
jmp free4; and print it out.
free3: mov dx, offset msg1; illegal drive, print error
free4: mov ah, 9; print the string whose address
int 21h; is in DX.
ret; then return to DOS.
free endp
; Convert 32 bit binary value to ASCII string.
;
; Call with DX: AX = signed 32 bit value
; CX = radix
; SI = last byte of area to store resulting string
; (Make sure enough room is available to store
; The string in the radix you have selected.)
;
; Destroys AX, BX, CX, DX, and SI.
;
bin_to_asc proc near; convert DX: AX to ASCII.
; Force storage of at least 1 digit.
mov byte ptr [si],''0''
or dx, dx; test sign of 32 bit value,
pushf; and save sign on stack.
jns bin1; jump if it was positive.
not dx; it was negative, take 2''s complement
not ax; of the value.
add ax, 1
adc dx, 0
bin1:; divide the 32 bit value by the radix
; To extract the next digit for the
; Forming string.
mov bx, ax; is the value zero yet?
or bx, dx
jz bin3; yes, we are done converting.
call divide; no, divide by radix.
add bl,''0''; convert the remainder to an ASCII digit.
cmp bl,''9''; we might be converting to hex ASCII,
jle bin2; jump if in range 0-9,
add bl,''A''-''9''-1; correct it if in range AF.
bin2: mov [si], bl; store this character into string.
dec si; back up through string,
jmp bin1; and do it again.
bin3:; restore sign flag,
popf; was original value negative?
jns bin4; no, jump
; Yes, store sign into output string.
mov byte ptr [si ],''-''
bin4: ret; back to caller.
bin_to_asc endp
; General purpose 32 bit by 16 bit unsigned divide.
; This must be used instead of the plain machine unsigned divide
; For cases where the quotient may overflow 16 bits (for example,
; Dividing 100,000 by 2). If called with a zero divisor, this
; Routine returns the dividend unchanged and gives no warning.
;
; Call with DX: AX = 32 bit dividend
; CX = divisor
;
; Returns DX: AX = quotient
; BX = remainder
; CX = divisor (unchanged)
;
divide proc near; Divide DX: AX by CX
jcxz div1; exit if divide by zero
push ax; 0: dividend_upper / divisor
mov ax, dx
xor dx, dx
div cx
mov bx, ax; BX = quotient1
pop ax; remainder1: dividend_lower / divisor
div cx
xchg bx, dx; DX: AX = quotient1: quotient2
div1: ret; BX = remainder2
divide endp
cseg ends
data segment para public''DATA''
output db cr, lf
outputa db 10 dup (blank)
db''bytes free on drive''
outputb db''x:'', cr, lf, eom
msg1 db cr, lf
db''That disk drive does not exist.''
db cr, lf, eom
msg2 db cr, lf
db''Requires DOS version 2 or greater.''
db cr, lf, eom
data ends
stack segment para stack''STACK''
db 64 dup (?)
stack ends
end free
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