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From: ls0@engr.uark.edu (LI SHENG)
Newsgroups: comp.sys.handhelds
Subject: Re: ** NEED CRC FOR USE IN ASC->  help.
Summary: RE: ** NEED CRC FOR USE IN ASC->  help
Keywords: crc
Message-ID: <5786@uafhp.uark.edu>
Date: 2 Jan 91 08:40:08 GMT
References: <277f5c07:1536comp.sys.handhelds@hpcvbbs.UUCP>
Sender: netnews@uafhp.uark.edu
Lines: 119

akcs.monosmith@hpcvbbs.UUCP (bryan monosmith) writes:
> HELP someone! I have ASC-> , and can use it on examples. I can also
> write my own code- BUT... how do I generate the 4 nibble checksum
> required by ASC-> ??  Am I missing something?


The following C program will calculate the CRC for an object string of 
the HP48SX.  This program only works for the HP48SX object strings.
The string can only contain 0,1,2,...,F.  No other character is allowed.

The following is the procedure to generate a ASC\-> string :
Let's say way want a code object contain only one instruction:

               call.a #12345

The machine code for the above instruction is 8F54321.  The HP48SX
internal storage for this code is:

              CCD20C00008F54321
             |    ||   ||      |   
             /      |        \
           /        |         \
         /          |           \
    prolog        object         machine    
   for code       length           code

Now, store this string in a file called TEST(or any name you like) and 
run the CRC program like this :

        crc test

You will get the resulte :

         The check sum is : # 3aa9h

Take this number, append it to the above string in reverse order.  
The resulting string should look like :

               CCD20C0008F543219AA3
                               ^^^^ <----- in reverse order

This string now is ready for ASC\->.

Transfer the above string to HP48SX as ASCII object and put it on the 
first level of the stack and then ASC\->.

      1: "CCD20C00008F543219AA3"  ASC\->  1:         code

Finished.

If the string is too long, you need to break it up in certain length.

The process can be done automaticly.  If there is enough interest, I will
finish that part of the program.  Mail me to :

                 ls0@engr.uark.edu

Li Sheng
Computer Science Engineering
University of Arkansas

----------  The program  CUT-----------------------------------------
            

/**************************************************************/
/*    Programmer : Li Sheng                                   */
/*    Time : 1-1-1991                                         */
/*    Email : ls0@engr.uark.edu                               */
/*                                                            */
/**************************************************************/ 
#include <stdio.h>

main(argc, argv)
char **argv;
{
   unsigned int i;
   FILE *infile;
   unsigned int crc=0, calc_crc();
   unsigned char *c, string_in[80];

   if(argc != 2)
   {
      printf("ERROR!!!!\n");
      printf("Format: crc file_name\n");
      exit();
   }
   if((infile=fopen(argv[1],"r")) == NULL)
   {
      printf("File does not exist\n");
      exit();
   }
   while(fgets(string_in,80, infile))
   {
      c = string_in;
      while(((*c>='0')&&(*c<='9'))||((*c>='A')&&(*c<='F')))
      {
         if(*c < 58) i = *c - 48;
         else i = *c - 55;
         crc = calc_crc(crc, i);
         c++;
      }
   }
   printf("The check sum is : # %xh\n",crc);
   fclose(infile);
}
 
unsigned int calc_crc(crc, i)
unsigned int crc, i;
{
   unsigned int q;
   q = (((crc^i) & 15) * 4225) ^(crc / 16);
   return q;
}