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package IO::Compress::Gzip::Constants;

use strict ;
use warnings;
use bytes;

require Exporter;

our ($VERSION, @ISA, @EXPORT, %GZIP_OS_Names);
our ($GZIP_FNAME_INVALID_CHAR_RE, $GZIP_FCOMMENT_INVALID_CHAR_RE);

$VERSION = '2.015';

@ISA = qw(Exporter);

@EXPORT= qw(

    GZIP_ID_SIZE
    GZIP_ID1
    GZIP_ID2

    GZIP_FLG_DEFAULT
    GZIP_FLG_FTEXT
    GZIP_FLG_FHCRC
    GZIP_FLG_FEXTRA
    GZIP_FLG_FNAME
    GZIP_FLG_FCOMMENT
    GZIP_FLG_RESERVED

    GZIP_CM_DEFLATED

    GZIP_MIN_HEADER_SIZE
    GZIP_TRAILER_SIZE

    GZIP_MTIME_DEFAULT
    GZIP_XFL_DEFAULT
    GZIP_FEXTRA_HEADER_SIZE
    GZIP_FEXTRA_MAX_SIZE
    GZIP_FEXTRA_SUBFIELD_HEADER_SIZE
    GZIP_FEXTRA_SUBFIELD_ID_SIZE
    GZIP_FEXTRA_SUBFIELD_LEN_SIZE
    GZIP_FEXTRA_SUBFIELD_MAX_SIZE

    $GZIP_FNAME_INVALID_CHAR_RE
    $GZIP_FCOMMENT_INVALID_CHAR_RE

    GZIP_FHCRC_SIZE

    GZIP_ISIZE_MAX
    GZIP_ISIZE_MOD_VALUE


    GZIP_NULL_BYTE

    GZIP_OS_DEFAULT

    %GZIP_OS_Names

    GZIP_MINIMUM_HEADER

    );

# Constant names derived from RFC 1952

use constant GZIP_ID_SIZE                     => 2 ;
use constant GZIP_ID1                         => 0x1F;
use constant GZIP_ID2                         => 0x8B;

use constant GZIP_MIN_HEADER_SIZE             => 10 ;# minimum gzip header size
use constant GZIP_TRAILER_SIZE                => 8 ;


use constant GZIP_FLG_DEFAULT                 => 0x00 ;
use constant GZIP_FLG_FTEXT                   => 0x01 ;
use constant GZIP_FLG_FHCRC                   => 0x02 ; # called CONTINUATION in gzip
use constant GZIP_FLG_FEXTRA                  => 0x04 ;
use constant GZIP_FLG_FNAME                   => 0x08 ;
use constant GZIP_FLG_FCOMMENT                => 0x10 ;
#use constant GZIP_FLG_ENCRYPTED              => 0x20 ; # documented in gzip sources
use constant GZIP_FLG_RESERVED                => (0x20 | 0x40 | 0x80) ;

use constant GZIP_XFL_DEFAULT                 => 0x00 ;

use constant GZIP_MTIME_DEFAULT               => 0x00 ;

use constant GZIP_FEXTRA_HEADER_SIZE          => 2 ;
use constant GZIP_FEXTRA_MAX_SIZE             => 0xFF ;
use constant GZIP_FEXTRA_SUBFIELD_ID_SIZE     => 2 ;
use constant GZIP_FEXTRA_SUBFIELD_LEN_SIZE    => 2 ;
use constant GZIP_FEXTRA_SUBFIELD_HEADER_SIZE => GZIP_FEXTRA_SUBFIELD_ID_SIZE +
                                                 GZIP_FEXTRA_SUBFIELD_LEN_SIZE;
use constant GZIP_FEXTRA_SUBFIELD_MAX_SIZE    => GZIP_FEXTRA_MAX_SIZE - 
                                                 GZIP_FEXTRA_SUBFIELD_HEADER_SIZE ;


if (ord('A') == 193)
{
    # EBCDIC 
    $GZIP_FNAME_INVALID_CHAR_RE = '[\x00-\x3f\xff]';
    $GZIP_FCOMMENT_INVALID_CHAR_RE = '[\x00-\x0a\x11-\x14\x16-\x3f\xff]';
    
}
else
{
    $GZIP_FNAME_INVALID_CHAR_RE       =  '[\x00-\x1F\x7F-\x9F]';
    $GZIP_FCOMMENT_INVALID_CHAR_RE    =  '[\x00-\x09\x11-\x1F\x7F-\x9F]';
}            

use constant GZIP_FHCRC_SIZE        => 2 ; # aka CONTINUATION in gzip

use constant GZIP_CM_DEFLATED       => 8 ;

use constant GZIP_NULL_BYTE         => "\x00";
use constant GZIP_ISIZE_MAX         => 0xFFFFFFFF ;
use constant GZIP_ISIZE_MOD_VALUE   => GZIP_ISIZE_MAX + 1 ;

# OS Names sourced from http://www.gzip.org/format.txt

use constant GZIP_OS_DEFAULT=> 0xFF ;
%GZIP_OS_Names = (
    0   => 'MS-DOS',
    1   => 'Amiga',
    2   => 'VMS',
    3   => 'Unix',
    4   => 'VM/CMS',
    5   => 'Atari TOS',
    6   => 'HPFS (OS/2, NT)',
    7   => 'Macintosh',
    8   => 'Z-System',
    9   => 'CP/M',
    10  => 'TOPS-20',
    11  => 'NTFS (NT)',
    12  => 'SMS QDOS',
    13  => 'Acorn RISCOS',
    14  => 'VFAT file system (Win95, NT)',
    15  => 'MVS',
    16  => 'BeOS',
    17  => 'Tandem/NSK',
    18  => 'THEOS',
    GZIP_OS_DEFAULT()   => 'Unknown',
    ) ;

use constant GZIP_MINIMUM_HEADER =>   pack("C4 V C C",  
        GZIP_ID1, GZIP_ID2, GZIP_CM_DEFLATED, GZIP_FLG_DEFAULT,
        GZIP_MTIME_DEFAULT, GZIP_XFL_DEFAULT, GZIP_OS_DEFAULT) ;


1;