Using Assembler with C

This  program  is an attempt to demonstrate the use  of  assembly 
language  routines  with C.  The whole idea is to write the  time 
critical routines in ASM for it's obvious superiority (speedwise) 
and call them from your C program as a function (with or  without 
parameters) with a minimum of hassle. This procedure doesn't seem 
to be too well documented, at least not in the books I have or in 
the doc that is sold with Lattice C; the compiler used here.    

The  latest  version of Lattice has a new function called  INTDOS 
that generates a DOS function call.  This, of course would be the 
easy  way  to  do  the two things I  did,  namely  CLS  and  CPOS 
(positions  the cursor).  But there will be times we need  to  do 
things *this* way; that is the reason for this study. 
        
I  hope  you find this information useful;  I have tried hard  to 
keep  it error free.  If I have failed in this,  or if  you  have 
suggestions,  comments,  or criticisms,  I'd be very glad to hear 
them.    

My current UID is 74176,3051 but I don't expect it to be so after 
the middle of November 84.

   ********************************************************** 
        
This  function will display a number of text strings (defined  in 
the header) centered on the screen.      
       
If  you  wish  to develop a working  program  here,  extract  the 
listings  from this text file,  complile the C program,  assemble 
the  two .ASM files to .OBJ files,  and LINK the  three  together 
with C[S].OBJ, and LCS.LIB.

Unix  C compilers are usually initiated by issuing the command CC 
(presumably for C Compiler!) and the .C source filespec.  If  you 
are  using  Lattice  (as I am) you don't get to do  it  that  way 
unless  you use a batch file  with that name.  While we're at  it 
(writing  the  .BAT file so we can issue 'CC filespec'  like  the 
'big  boys') we may as well have CC do something for us!  Here is 
what my .BAT looks like: 


 
lc1 %1                           ;1st pass.
IF NOT EXIST %1.q GOTO quit      ;An error will keep the .Q file
                                 ; from being generated, and we
                                 ; might as well stop, eh?!
lc2 %1                           ;If it's there, let's do pass 2.
IF NOT EXIST %1.obj GOTO quit    ;Same story, here.
                                 ;This is the confusing part.....
link cs %1 %2 %3 %4,%1,,lcs;     ;%2, %3, etc are for 'extra' .OBJ 
                                 ; modules if we have them; else 
                                 ; they're ignored.
DIR %1.*                         ;We wanna see what we've done, right?!
:quit

Just make sure the first filespec you link with is the file  with 
main  () in it.  The next three can be  CLS.OBJ,  CPOS.OBJ,  etc. 
Also,  be sure you DON'T include the .ext's in the filenames. The 
compiler and linker are smart enough to figure out what they are.

So, you could issue this command:

     CC MYPROG CLS CPOS <ENTER> 
        
where  MYPROG.C  and CLS.OBJ and CPOS.OBJ are all on the  default 
disk.  The  resulting .EXE file (MYPROG.EXE) will have  the  .ASM 
code included,  and our work will be complete. As always, be sure 
you save everything BEFORE you try to run the program. You'd hate 
to start all over, right?


                 
#include <stdio.h>

/* *********************************************************** */
/*   These DEFINES can be changed to change output.            */

#define  LINE1   "BootStrap Micro"
#define  LINE2   "R. B. Miller"
#define  LINE3   "P. O. Box 6221"
#define  LINE4   "Stanford, Calif 94305"
#define  LINE5   "415-960-3773"
#define  NLINES   5                 /* Nmbr of lines of text. */

/* *********************************************************** */


#define  LLEN         80         /* Line length */
#define  SCRN_LINES   25         /* Nmbr of lines on scrn. */
#define  COL          0          /* Always position to col 0. */


static char *data [5] = {
                              LINE1,
                              LINE2,
                              LINE3,
                              LINE4,
                              LINE5  
                                         } ;



MAIN ()                           /* Display and center text */

{ 
     int i, j, inset ;
     static char *string; 

        cls ();                         /* Clear the screen. */
        cpos ((SCRN_LINES - NLINES) / 2 , COL );/* Pos the cursor.   */

        for  (i=0 ; i <= NLINES-1 ; i++ )
        {
        
                string =  data[i];
                
                for  ( j = 1 ; j <= (( LLEN - strlen ( string )) / 2 ); j++ )
                    putchar ( ' ' );
                      
                printf ( "%s\n",string );
                   
        } 

  
       cpos ( 22 , COL );                              /* Pos the cursor.  */

}






title   clear screen function
name    cls
page    ,132

comment @

This is the source code for the 'C' function CLS.  This
function does exactly the same thing as the DOS COMmand
by the same name except this can be LINKed with a 'C'
module and called as a function:
                                          
USAGE:  no variable preparation, no return value,
                                                  
            CLS () ;
@
                                 
                                
                                
pgroup  group   prog
prog    segment byte    public  'prog'
public  cls
                                
assume  cs:pgroup
                                
cls     proc    near            ;CLS and HOME the cursor.
                                
                                
        mov     ax,0600h        ;Scroll the whole screen.
        mov     cx,0            ;from 0,0 to...
        mov     dx,184fh        ;ROW 24, COL 79.
        mov     bh,7            ;'NORMAL' attribute.
        int     10h
                                        
        mov     ah,2            ;SET_CURS function.
        mov     dx,0            ;ROW, COL 0,0.
        mov     bh,0            ;Page 0.
        int     10h
                                
        ret
                                
 cls     endp
 prog    ends
         end

title        cursor position function
name         cpos
page         ,132 
                                
comment @
                                 
This is the source code for the 'C' function CPOS ( ROW , COL );
that does exactly what it sounds like it does.. it positions
the cursor at the ROW and COLumn indicated in the arguments.
                                        
Usage:     
                                
INT ROW , COL ;
                                                
/* Assign values 0,0  to  24,79  */
                                                
CPOS ( ROW , COL ) ;
@
                                
                                
prog         segment      byte     public    'prog'
public       cpos
                                
assume       cs:pgroup
                                
cpos         proc         near
                                
             push         bp
             mov          bp,sp
             mov          dx,[bp+4]          ;Skip over return address,
                                             ; and saved bp, and 
                                             ; get left parm (ROW).
             mov          ax,[bp+6]          ;Get 2nd parm (COL).
             pop          bp
                                             
             mov          dh,dl              ;ROW in DH,
             mov          dl,al              ;COL in DL.
             mov          bh,0               ;Page 0.
             mov          ah,2               ;Funct 2 'SET_CPOS'.
                                             
             int          10h
             ret
                                
                                             
 cpos         endp
 prog         ends
              end

-------------------------
Downloaded  from  the IBMPC special interest area of  CompuServe, 
uploaded to PCanada by Bob Leigh, PC1022.