/******************************************************************************/
/*      SERNO3.C        Version 1               Revision 00    2 January 1985 */
/******************************************************************************/

/******************************************************************************/
/*                              cpm_ser_num                                   */
/*                  Copyright (c) 1985 by Paul M. Sittler                     */
/*                  No rights reserved, or all rights reversed. . .           */
/******************************************************************************/
cpm_ser_num()
{
/******************************************************************************/
/* SERNO3.C was inspired by SERNO2.ASM by Charles Horn, dtd 31 January 1984.  */
/*      I coded it into 'c' so that I could add this function to some of my   */
/* programs.  While I was at it, I thought I would write it up as a tutorial  */
/* and show how 'c' could do most anything that could be done in assembler.   */
/* The finished program, of course, is somewhat larger and a trifle slower    */
/* than SERNO2.COM, but it took me a LOT less time to code it in 'c' than it  */
/* would have taken me in assembler.  Enjoy, <pms>. . .                       */
/*                                                                            */
/* Notes and tutorial on the CP/M serial number:                              */
/*                                                                            */
/*    The CP/M serial number is located at the beginning of the BDOS Page     */
/* of memory.  This is exactly six bytes ahead of the BDOS entry address      */
/* that is accessed by the BDOS jump at 0005H.  It usually consists of        */
/* three decimal numbers of the form nnn-nnnn-nn, or num1-num2-num3.  Num1    */
/* and num3 are one-byte numbers, and num2 is a two byte number.  As an       */
/* example, a serial number of (decimal) 123-4567-8,                          */
/*      would be coded as (hexadecimal) 7B-11D7-08.                           */
/*                                                                            */
/*    At the actual BDOS Page location, the numbers would appear as:          */
/*                                                                            */
/*       At  (BDOS ENTRY - 6) >>>>---->   7B  08  00  00  11  D7              */
/*                                        ||  ||  ||  ||  ||  ||              */
/*           Serial Number num1  ---------++  ||  ||  ||  ||  ||              */
/*           Serial Number num3  -------------++  ||  ||  ||  ||              */
/*           Zero filled bytes   -----------------++--++  ||  ||              */
/*           Serial Number num2  -------------------------++--++              */
/*                                                                            */
/*     The same number string is coded into MOVCPM.COM, starting at address   */
/* (usually) 1200H.  When MOVCPM runs, it checks to see that these two numbers*/
/* match.  If they do NOT match, MOVCPM reports "SYNCHRONIZATION ERROR" and   */
/* quits.  This will prevent one from generating a system image in memory     */
/* for customization.                                                         */
/*                                                                            */
/*     This program reads the BDOS entry address from the BDOS jump at 005H,  */
/* sets a pointer to the beginning of the serial number, reads the serial     */
/* number into memory, and prints them out.                                   */
/*                                                                            */
/******************************************************************************/

/******************************************************************************/
/*                              local variables                               */
/******************************************************************************/

int Bdos,               /* address in memory of the BDOS entry */
     sernum_addr;       /* address in memory of the serial number */
unsigned serno2;        /* unsigned so it can be bigger than +/- 32760 */
char *ptr,              /* all purpose pointer */
     serno1,            /* serno1 and two are only one byte numbers */
     serno3;            /* so declare them as character */

/******************************************************************************/
/*                              code starts here                              */
/******************************************************************************/

    ptr = 6;                            /*set pointer to BDOS entry address */
    Bdos = (*ptr++) + (*ptr++ << 8);    /* Bdos entry address */
    sernum_address = Bdos - 6;          /* Back up six bytes */
    ptr = sernum_address;               /* point to serial number address */
    serno1 = (*ptr++);                  /* store value at pointer into serno1 */
    serno3 = (*ptr++);
    ptr += 2;                           /* skip those zeros */
    serno2 = (*ptr++ << 8) + (*ptr);    /* Most significant bit first, */
					/* Least significant bit second. */

    printf("\n\tOperating system serial number is at location %04x.",
				sernum_address);
    printf("\n\tserial number is %02x-%04x-%02x hex,",
				serno1,serno2,serno3);
    printf("\n\t                or %d-%u-%03d decimal.\n",
				serno1,serno2,serno3);
}