/*
 * crc.c --
 *
 *	Implements and registers message digest generator CRC.
 *
 *
 * Copyright (c) 1996 Andreas Kupries (andreas_kupries@users.sourceforge.net)
 * All rights reserved.
 *
 * Permission is hereby granted, without written agreement and without
 * license or royalty fees, to use, copy, modify, and distribute this
 * software and its documentation for any purpose, provided that the
 * above copyright notice and the following two paragraphs appear in
 * all copies of this software.
 *
 * IN NO EVENT SHALL I LIABLE TO ANY PARTY FOR DIRECT, INDIRECT, SPECIAL,
 * INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF THIS
 * SOFTWARE AND ITS DOCUMENTATION, EVEN IF I HAVE BEEN ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 * I SPECIFICALLY DISCLAIM ANY WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND
 * I HAVE NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES,
 * ENHANCEMENTS, OR MODIFICATIONS.
 *
 * CVS: $Id: crc.c,v 1.4 2000/08/09 19:13:17 aku Exp $
 */

#include "transformInt.h"
#include "crc.h"

/*
 * Generator description
 * ---------------------
 *
 * The CRC algorithm is used to compute a message digest.
 * The polynomial is taken from PGP (parts of the code too).
 */

#define DIGEST_SIZE               (CRCBYTES)
#define CTX_TYPE                  crcword

/*
 * Declarations of internal procedures.
 */

static void MDcrc_Start     _ANSI_ARGS_ ((VOID* context));
static void MDcrc_Update    _ANSI_ARGS_ ((VOID* context, unsigned int character));
static void MDcrc_UpdateBuf _ANSI_ARGS_ ((VOID* context, unsigned char* buffer, int bufLen));
static void MDcrc_Final     _ANSI_ARGS_ ((VOID* context, VOID* digest));

/*
 * Generator definition.
 */

static Trf_MessageDigestDescription mdDescription = {
  "crc",
  sizeof (CTX_TYPE),
  DIGEST_SIZE,
  MDcrc_Start,
  MDcrc_Update,
  MDcrc_UpdateBuf,
  MDcrc_Final,
  NULL
};

/*
 * Additional declarations
 */

static crcword CrcTable [256]; /* THREADING: serialize initialization */

static void
GenCrcLookupTable _ANSI_ARGS_ ((crcword polynomial));

/*
 *------------------------------------------------------*
 *
 *	TrfInit_CRC --
 *
 *	------------------------------------------------*
 *	Register the generator implemented in this file.
 *	------------------------------------------------*
 *
 *	Sideeffects:
 *		As of 'Trf_Register'.
 *
 *	Result:
 *		A standard Tcl error code.
 *
 *------------------------------------------------------*
 */

int
TrfInit_CRC (interp)
Tcl_Interp* interp;
{
  GenCrcLookupTable (PRZCRC);

  return Trf_RegisterMessageDigest (interp, &mdDescription);
}

/*
 *------------------------------------------------------*
 *
 *	MDcrc_Start --
 *
 *	------------------------------------------------*
 *	Initialize the internal state of the message
 *	digest generator.
 *	------------------------------------------------*
 *
 *	Sideeffects:
 *		As of the called procedure.
 *
 *	Result:
 *		None.
 *
 *------------------------------------------------------*
 */

static void
MDcrc_Start (context)
VOID* context;
{
  /* call md specific initialization here */

  *((crcword*) context) = CRCINIT;
}

/*
 *------------------------------------------------------*
 *
 *	MDcrc_Update --
 *
 *	------------------------------------------------*
 *	Update the internal state of the message digest
 *	generator for a single character.
 *	------------------------------------------------*
 *
 *	Sideeffects:
 *		As of the called procedure.
 *
 *	Result:
 *		None.
 *
 *------------------------------------------------------*
 */

static void
MDcrc_Update (context, character)
VOID* context;
unsigned int   character;
{
  /* call md specific update here */
#define UP(ctx)   ((ctx) << 8)
#define DOWN(ctx) ((ctx) >> CRCSHIFTS)

  crcword       accu;
  unsigned char buf = character;

  accu = *((crcword*) context);
  accu = UP (accu) ^ CrcTable [(unsigned char) (DOWN (accu)) ^ buf];

  *((crcword*) context) = accu;

#undef UP
#undef DOWN
}

/*
 *------------------------------------------------------*
 *
 *	MDcrc_UpdateBuf --
 *
 *	------------------------------------------------*
 *	Update the internal state of the message digest
 *	generator for a character buffer.
 *	------------------------------------------------*
 *
 *	Sideeffects:
 *		As of the called procedure.
 *
 *	Result:
 *		None.
 *
 *------------------------------------------------------*
 */

static void
MDcrc_UpdateBuf (context, buffer, bufLen)
VOID* context;
unsigned char* buffer;
int   bufLen;
{
  /* call md specific update here */
#define UP(ctx)   ((ctx) << 8)
#define DOWN(ctx) ((ctx) >> CRCSHIFTS)

  crcword accu;
  int     i;

  accu = *((crcword*) context);

  for (i=0; i < bufLen; i++) {
    accu = UP (accu) ^ CrcTable [(unsigned char) (DOWN (accu)) ^ (buffer [i])];
  }

  *((crcword*) context) = accu;

#undef UP
#undef DOWN
}

/*
 *------------------------------------------------------*
 *
 *	MDcrc_Final --
 *
 *	------------------------------------------------*
 *	Generate the digest from the internal state of
 *	the message digest generator.
 *	------------------------------------------------*
 *
 *	Sideeffects:
 *		As of the called procedure.
 *
 *	Result:
 *		None.
 *
 *------------------------------------------------------*
 */

static void
MDcrc_Final (context, digest)
VOID* context;
VOID* digest;
{
  /* call md specific finalization here */

  crcword crc = maskcrc (* ((crcword*) context));
  char*   out = (char*) digest;

  /* -*- PGP -*-, was outcrc, BIGENDIAN output */
  /* DEPENDENT on CRCBYTES !!, only a value of 3 is supported here */

  out [0] = (char) ((crc >> 16) & 0xff);
  out [1] = (char) ((crc >>  8) & 0xff);
  out [2] = (char) ((crc >>  0) & 0xff);
  /* -*- PGP -*- */
}

/*
 * Initialize lookup table for crc calculation.
 */

static void
GenCrcLookupTable (poly)
crcword poly;
{
  /* -*- PGP -*-, was 'mk_crctbl' */
  int i;
  crcword t, *p, *q;

  TrfLock; /* THREADING: serialize initialization */

  p = q = CrcTable;

  *q++ = 0;
  *q++ = poly;

  for (i = 1; i < 128; i++)
    {
      t = *++p;
      if (t & CRCHIBIT)
	{
	  t <<= 1;
	  *q++ = t ^ poly;
	  *q++ = t;
	}
      else
	{
	  t <<= 1;
	  *q++ = t;
	  *q++ = t ^ poly;
	}
    }

  TrfUnlock;
  /* -*- PGP -*- */
}