/*  ARC - Archive utility - ARCSVC

(C) COPYRIGHT 1985 by System Enhancement Associates; ALL RIGHTS RESERVED

    By:  Thom Henderson

    Description:
         This file contains service routines needed to maintain an archive.

    Language:
         Computer Innovations Optimizing C86
*/
#include <stdio.h>
#include "arc.h"

openarc(chg)                           /* open archive */
int chg;                               /* true to open for changes */
{
    FILE *fopen();                     /* file opener */

    if(!(arc=fopen(arcname,"r")))
    {    if(chg)
              printf("Creating new archive: %s\n",arcname);
         else abort("Cannot read archive: %s",arcname);
    }

    if(chg)                            /* if opening for changes */
         if(!(new=fopen(newname,"w")))
              abort("Cannot create archive copy: %s",newname);
}

closearc(chg)                          /* close an archive */
int chg;                               /* true if archive was changed */
{
    if(arc)                            /* if we had an initial archive */
         fclose(arc);                  /* then close it */

    if(chg)                            /* if things have changed */
    {
#if unix
         fclose(new);                  /* close the new copy */
         setstamp(newname,arcdate,arctime);/* archive matches newest file */
#else
         setstamp(new,arcdate,arctime);/* archive matches newest file */
         fclose(new);                  /* close the new copy */
#endif

         if(arc)                       /* if we had an original archive */
         {    if(keepbak)              /* if a backup is wanted */
              {    unlink(bakname);    /* erase any old copies */
                   if(rename(arcname,bakname))
                        abort("Cannot rename %s to %s",arcname,bakname);
                   printf("Keeping backup archive: %s\n",bakname);
              }
              else if(unlink(arcname))
                   abort("Cannot delete old archive: %s",arcname);
         }

         if(rename(newname,arcname))
              abort("Cannot rename %s to %s",newname,arcname);
    }
}

/* CRC computation logic

   The logic for this method of calculating the CRC 16 bit polynomial
   is taken from an article by David Schwaderer in the April 1985
   issue of PC Tech Journal.
*/

static int crctab[] =                  /* CRC lookup table */
{   0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
    0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
    0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
    0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
    0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
    0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
    0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
    0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
    0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
    0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
    0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
    0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
    0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
    0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
    0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
    0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
    0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
    0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
    0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
    0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
    0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
    0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
    0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
    0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
    0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
    0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
    0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
    0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
    0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
    0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
    0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
    0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
};
int addcrc(crc,c)                      /* update a CRC check */
int crc;                               /* running CRC value */
unsigned char c;                       /* character to add */
{
#if unix
    return (0xffff & (((crc>>8)&0x00ff) ^ crctab[(crc^c)&0x00ff]));
#else
    return ((crc>>8)&0x00ff) ^ crctab[(crc^c)&0x00ff];
#endif
}