//
// STORCRC.CPP
//
//  Source file for ArchiveLib 2.0
//
//  Copyright (c) Greenleaf Software, Inc. 1994-1996
//  All Rights Reserved
//
// CONTENTS
//
//  ccitt_32[ 256 ]
//  ALStorage::UpdateCrc()
//  ALStorage::GetCrc32()
//  ALStorageGetCrc32()
//  ALStorage::InitCrc32()
//  ALStorageInitCrc32()
//
// DESCRIPTION
//
//  This file contains all the modules used to calculate CRC32
//  values for ALStorage objects.
//
// REVISION HISTORY
//
//   February 14, 1996  2.0A : New release.
//

#include "arclib.h"
#if !defined( AL_IBM )
#pragma hdrstop
#endif

//
// This giant table is used by the CRC routines.  These are the coefficients
// for calculating the CCITT 32 bit CRC.  I typed these in from memory, so
// I hope they are correct.
//
static unsigned long ccitt_32[ 256 ] =
{
0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL, 0x076dc419L, 0x706af48fL, 0xe963a535L, 0x9e6495a3L,
0x0edb8832L, 0x79dcb8a4L, 0xe0d5e91eL, 0x97d2d988L, 0x09b64c2bL, 0x7eb17cbdL, 0xe7b82d07L, 0x90bf1d91L,
0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL, 0x1adad47dL, 0x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L,
0x136c9856L, 0x646ba8c0L, 0xfd62f97aL, 0x8a65c9ecL, 0x14015c4fL, 0x63066cd9L, 0xfa0f3d63L, 0x8d080df5L,
0x3b6e20c8L, 0x4c69105eL, 0xd56041e4L, 0xa2677172L, 0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL, 0xa50ab56bL,
0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L, 0x32d86ce3L, 0x45df5c75L, 0xdcd60dcfL, 0xabd13d59L,
0x26d930acL, 0x51de003aL, 0xc8d75180L, 0xbfd06116L, 0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L, 0xb8bda50fL,
0x2802b89eL, 0x5f058808L, 0xc60cd9b2L, 0xb10be924L, 0x2f6f7c87L, 0x58684c11L, 0xc1611dabL, 0xb6662d3dL,
0x76dc4190L, 0x01db7106L, 0x98d220bcL, 0xefd5102aL, 0x71b18589L, 0x06b6b51fL, 0x9fbfe4a5L, 0xe8b8d433L,
0x7807c9a2L, 0x0f00f934L, 0x9609a88eL, 0xe10e9818L, 0x7f6a0dbbL, 0x086d3d2dL, 0x91646c97L, 0xe6635c01L,
0x6b6b51f4L, 0x1c6c6162L, 0x856530d8L, 0xf262004eL, 0x6c0695edL, 0x1b01a57bL, 0x8208f4c1L, 0xf50fc457L,
0x65b0d9c6L, 0x12b7e950L, 0x8bbeb8eaL, 0xfcb9887cL, 0x62dd1ddfL, 0x15da2d49L, 0x8cd37cf3L, 0xfbd44c65L,
0x4db26158L, 0x3ab551ceL, 0xa3bc0074L, 0xd4bb30e2L, 0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL,
0x4369e96aL, 0x346ed9fcL, 0xad678846L, 0xda60b8d0L, 0x44042d73L, 0x33031de5L, 0xaa0a4c5fL, 0xdd0d7cc9L,
0x5005713cL, 0x270241aaL, 0xbe0b1010L, 0xc90c2086L, 0x5768b525L, 0x206f85b3L, 0xb966d409L, 0xce61e49fL,
0x5edef90eL, 0x29d9c998L, 0xb0d09822L, 0xc7d7a8b4L, 0x59b33d17L, 0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL,
0xedb88320L, 0x9abfb3b6L, 0x03b6e20cL, 0x74b1d29aL, 0xead54739L, 0x9dd277afL, 0x04db2615L, 0x73dc1683L,
0xe3630b12L, 0x94643b84L, 0x0d6d6a3eL, 0x7a6a5aa8L, 0xe40ecf0bL, 0x9309ff9dL, 0x0a00ae27L, 0x7d079eb1L,
0xf00f9344L, 0x8708a3d2L, 0x1e01f268L, 0x6906c2feL, 0xf762575dL, 0x806567cbL, 0x196c3671L, 0x6e6b06e7L,
0xfed41b76L, 0x89d32be0L, 0x10da7a5aL, 0x67dd4accL, 0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L, 0x60b08ed5L,
0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L, 0xd1bb67f1L, 0xa6bc5767L, 0x3fb506ddL, 0x48b2364bL,
0xd80d2bdaL, 0xaf0a1b4cL, 0x36034af6L, 0x41047a60L, 0xdf60efc3L, 0xa867df55L, 0x316e8eefL, 0x4669be79L,
0xcb61b38cL, 0xbc66831aL, 0x256fd2a0L, 0x5268e236L, 0xcc0c7795L, 0xbb0b4703L, 0x220216b9L, 0x5505262fL,
0xc5ba3bbeL, 0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L, 0xc2d7ffa7L, 0xb5d0cf31L, 0x2cd99e8bL, 0x5bdeae1dL,
0x9b64c2b0L, 0xec63f226L, 0x756aa39cL, 0x026d930aL, 0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x05005713L,
0x95bf4a82L, 0xe2b87a14L, 0x7bb12baeL, 0x0cb61b38L, 0x92d28e9bL, 0xe5d5be0dL, 0x7cdcefb7L, 0x0bdbdf21L,
0x86d3d2d4L, 0xf1d4e242L, 0x68ddb3f8L, 0x1fda836eL, 0x81be16cdL, 0xf6b9265bL, 0x6fb077e1L, 0x18b74777L,
0x88085ae6L, 0xff0f6a70L, 0x66063bcaL, 0x11010b5cL, 0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L,
0xa00ae278L, 0xd70dd2eeL, 0x4e048354L, 0x3903b3c2L, 0xa7672661L, 0xd06016f7L, 0x4969474dL, 0x3e6e77dbL,
0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L, 0x37d83bf0L, 0xa9bcae53L, 0xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L,
0xbdbdf21cL, 0xcabac28aL, 0x53b39330L, 0x24b4a3a6L, 0xbad03605L, 0xcdd70693L, 0x54de5729L, 0x23d967bfL,
0xb3667a2eL, 0xc4614ab8L, 0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL, 0x2d02ef8dL
};

//
// NAME
//
//  ALStorage::UpdateCrc()
//
// PLATFORMS/ENVIRONMENTS
//
//  Console  Windows  PM
//  C++
//
// SHORT DESCRIPTION
//
//  Update the CRC to account for a batch of new characters.
//
// C++ SYNOPSIS
//
//  #include "arclib.h"
//
//  void ALStorage::UpdateCrc( size_t count );
//
// C SYNOPSIS
//
//  None, this is an internal protected function.
//
// VB SYNOPSIS
//
//  None, this is an internal protected function.
//
// DELPHI SYNOPSIS
//
//  None, this is an internal protected function.
//
// ARGUMENTS
//
//  count  :  The number of characters to process in the I/O buffer.  This
//            is usually called by FlushBuffer() or LoadBuffer() just before
//            or just after a read/write to/from the physical device.
//
// DESCRIPTION
//
//  If CRC checking has been turned on for the storage object, this
//  routine will be called every time LoadBuffer() or FlushBuffer()
//  are called.  It does CRC checking on a buffer full of data at
//  a time.  Hopefully this means the compiler can optimize the
//  heck out of this code.
//
//  Note that CRC checking is an expense that we don't necessarily want to
//  incur when reading or writing a file, so it is normally turned off.  We
//  turn it on when inserting/extracting data to/from an archive, to provide
//  error checking after decompression.
//
// RETURNS
//
//  Nothing.
//
// EXAMPLE
//
// SEE ALSO
//
//  ALStorage::InitCrc32(), ALStorage::GetCrc32()
//
// REVISION HISTORY
//
//   February 14, 1996  2.0A : New release.
//

void AL_PROTO
ALStorage::UpdateCrc( size_t count )  /* Tag protected function */
{
    unsigned char *p = (unsigned char *) mpcBuffer;
    while ( count-- != 0 )
        mlCrc32 = ( ( mlCrc32 >> 8 ) & 0x00FFFFFFL ) ^
                   ( ccitt_32[ ( (int) mlCrc32 ^ *p++ ) & 0xff ] );
}

//
// NAME
//
//  ALStorage::GetCrc32()
//
// PLATFORMS/ENVIRONMENTS
//
//  Console  Windows  PM
//  C++  C  VB  Delphi
//
// SHORT DESCRIPTION
//
//  Retrieve the calculated CRC from a storage object.
//
// C++ SYNOPSIS
//
//  #include "arclib.h"
//
//  long ALStorage::GetCrc32()
//
// C SYNOPSIS
//
//  #include "arclib.h"
//
//  long ALStorageGetCrc32( hALStorage this_object );
//
// VB SYNOPSIS
//
//  Declare Function ALStorageGetCrc32 Lib "AL20FW"
//    (ByVal this_object&) As Long
//
// DELPHI SYNOPSIS
//
//  function ALStorageGetCrc32( this_object : hALStorage ) : LongInt;
//
// ARGUMENTS
//
//  this_object  :  A reference or pointer to the ALStorage object that
//                  contains the CRC32 value that we want.  Note that the C++
//                  version of this call doesn't have an explicit argument
//                  here, since it has access to 'this' implicitly.
//
// DESCRIPTION
//
//  This function is used to get the CRC-32 of a storage object.  But it
//  does a little bit more than just give you the CRC.  First, it makes
//  sure the buffers have been flushed, so that the CRC is accurate.  If
//  we didn't do this we might try to get the CRC on an incompletely
//  written file.
//
//  Once we get the CRC,the miUpdateCrcFlag is set to 0, which means
//  that from here on out the value will not be updated.  So retrieving
//  the CRC means you are no longer interested in further calculation.
//  It also means you can trust the value you just read, because it
//  will never be modified again.
//
//  One important thing to note.  The CRC-32 value is no good until it has
//  either been calculated by reading or writing an entire file.
//
// RETURNS
//
//  The current value of the CRC-32.
//
// EXAMPLE
//
// SEE ALSO
//
//  ALStorage::InitCrc32()
//
// REVISION HISTORY
//
//   February 14, 1996  2.0A : New release.
//

long AL_PROTO
ALStorage::GetCrc32()  /* Tag public function */
{
    if ( IsOpen() && miUpdateCrcFlag )
        FlushBuffer();
    miUpdateCrcFlag = 0;
    return mlCrc32;
}

#if !defined( AL_NO_C )

extern "C" AL_LINKAGE long AL_FUNCTION
ALStorageGetCrc32( hALStorage this_object )  /* Tag public function */
{
    AL_ASSERT_OBJECT( this_object, ALStorage, "ALStorageGetCrc32" );
    return ( (ALStorage *) this_object )->GetCrc32();
}

#endif

//
// NAME
//
//  ALStorage::InitCrc32()
//
// PLATFORMS/ENVIRONMENTS
//
//  Console  Windows  PM
//  C++  C  VB  Delphi
//
// SHORT DESCRIPTION
//
//  Begin the process of calculating a CRC for a given object.
//
// C++ SYNOPSIS
//
//  #include "arclib.h"
//
//  void ALStorage::InitCrc32( unsigned long seed = 0xffffffffL );
//
// C SYNOPSIS
//
//  #include "arclib.h"
//
//  void ALStorageInitCrc32( hALStorage this_object, long seed );
//
// VB SYNOPSIS
//
//  Declare Sub ALStorageInitCrc32 Lib "AL20FW"
//    (ByVal this_object&, ByVal seed&)
//
// DELPHI SYNOPSIS
//
//  procedure ALStorageInitCrc32( this_object : hALStorage; seed : LongInt );
//
// ARGUMENTS
//
//  this_object  :  A reference or pointer to the ALStorage object that
//                  is going to begin CRC calculation.  Note that the C++
//                  version of this call doesn't have an explicit argument
//                  here, since it has access to 'this' implicitly.
//
//  seed  :  The long value to start the CRC off at.  There is probably
//           no reason to change this from the default value, although
//           I won't be surprised if someone comes up with one.
//
// DESCRIPTION
//
//  Calling this function kicks off the CRC calculation for a given
//  storage object. This should be done immediately after the object is
//  opened.  Once the miUpdateCrcFlag is set, the CRC will be updated
//  every time a LoadBuffer() or FlushBuffer() is called.
//
// RETURNS
//
//  Nothing.
//
// EXAMPLE
//
// SEE ALSO
//
//  ALStorage::GetCrc32()
//
// REVISION HISTORY
//
//   February 14, 1996  2.0A : New release.
//

void AL_PROTO
ALStorage::InitCrc32( unsigned long seed /* = 0xffffffffL */ )  /* Tag public function */
{
    miUpdateCrcFlag = 1;
    mlCrc32 = seed;
}

#if !defined( AL_NO_C )

extern "C" AL_LINKAGE void AL_FUNCTION
ALStorageInitCrc32( hALStorage this_object, long seed )  /* Tag public function */
{
    AL_ASSERT_OBJECT( this_object, ALStorage, "ALStorageInitCrc32" );
    ( (ALStorage *) this_object )->InitCrc32( seed );
}

#endif