Assembly Source series of CLEANF

This is the past DOS era of the compilation of source code, although has passed, but for the study of the assembly is still helpful, assembly language is just a basic programmer language, most people can grasp, not necessarily in-depth research.

Name cleanf
Page 55,132
Title ' Cleanf-filter text file '
;
; Cleanf-a DOS 2.0 filter for word processing document files.
;
; Clean. ASM originally written by Ray Duncan
; Converted to DOS 2.0 filter cleanf. ASM by Bob Taylor.
;
; This is reads text from the standard input device and writes
; Filtered and transformed text to the standard output device.
;
; 1. The high bit of the all characters are stripped off.
; 2. Tabs are expanded.
; 3. Removes all control codes except
; Feeds, carriage returns, and form feeds.
; 4. Appends an end-of-file mark to the text, if
; The none is present in the input stream.
;
; Can is used to make a WordStar file acceptable for
; Other screens or line editors, and vice versa.
;
;
CR Equ 0DH; ASCII Carriage return
LF equ 0ah; ASCII line Feed
FF equ 0ch; ASCII Form Feed
EOF Equ 01ah; End-of-file Marker
tab EQU 09h; ASCII Tab Code
command equ 80h; Buffer for Command tail
; DOS 2.0 pre-defined Handles
stdin equ 0000; Standard input File
STDOUT equ 0001; Standard output file
stderr equ 0002; Standard error file
Stdaux equ 0003; Standard auxilliary file
STDPRN equ 0004; Standard printer file
CSEG segment para public ' CODE '
Assume Cs:cseg,ds:cseg
ORG 100H; Start. COM at 100H
clean proc far; Entry point from Pc-dos.
Push DS; Push a long back
XOR Ax,ax; To DOS onto the stack.
Push AX
Clean3:call Get_char; Get a character from input.
and AL,7FH; Turn off the high bit.
CMP al,20h; Is it a control char?
Jae Clean4;　No. Write it to output.
CMP al,eof; Is it end of file?
Je clean6; Yes, go write EOF mark and exit.
CMP Al,tab; Is it a tab?
Je clean5; Yes, go expand it to spaces.
CMP AL,CR; Is it a carriage return?
Je clean35; Yes, go process it.
CMP AL,LF; Is it a line feed?
Je clean35; Yes, go process it.
CMP al,ff; Is it a form feed?
Jne clean3; No. Discard it.
Clean35:
MOV column,0; If it ' s a legit ctrl char,
JMP Clean45; We are should to back at column 0.
Clean4:inc column; If it ' s a Non-ctrl char,
CLEAN45:; Col = col + 1.
Call Put_char; Write the char to output.
Jnc clean3; If OK, go back for another char.
MOV bx,stderr;　Not OK. Set up to show error.
MOV Dx,offset err_msg
MOV Cx,err_msg_len; Error = Disk full.
MOV ah,40h; Write the error message
int 21h; To the standard error device. (CON:)
RET; Back to DOS.
Clean5:mov Ax,column; Tab code detected, must expand
CWD; Expand tabs to spaces.
MOV cx,8; Divide the current column counter
Idiv CX; By eight ...
Sub Cx,dx; Eight minus the remainder is the
Add column,cx; Number of spaces to send out to
Clean55:; Move to the next tab position.
Push CX
MOV al,20h
Call Put_char; Send an ASCII blank
Pop CX
Loop Clean55
JMP CLEAN3
Clean6:call Put_char; Write out the EOF mark,
RET; and return to DOS.
Clean ENDP
Get_char proc Near
MOV Bx,stdin; Get chars from Std. input
MOV cx,1; # of chars to get = 1
mov Dx,offset input_buffer; Location = Input_buffer
MOV ah,3fh
int 21h; Does the function call
or Ax,ax; Test # of Chars returned
JZ get_char1; If none, return EOF
MOV al,input_buffer; else, return to the char in AL
Ret
GET_CHAR1:
MOV al,eof; No chars read, return
RET; An end-of-file (EOF) mark.
Get_char ENDP
Put_char proc Near
MOV output_buffer,al; Put the char to write in buffer.
MOV bx,stdout; Write to Std. output
MOV cx,1; # of chars = 1
mov Dx,offset output_buffer; Location = Output_buffer
MOV ah,40h
int 21h; Does the function call
CMP ax,1; Check to the it is really done.
Jne put_char1
CLC; Really done. return carry = 0
RET; As success signal.
PUT_CHAR1:
STC; Not really done. return carry = 1
RET; As Error signal (device is full).
Put_char ENDP
Input_buffer DB 0
Output_buffer DB 0
Column DW 0
Err_msg DB CR,LF
DB ' Clean:disk is full. '
DB CR,LF
Err_msg_len equ (This byte)-(offset err_msg)
Cseg ends
End Clean