    -- arch-tag: CRC32 implementation in pure Haskell
    -- from http://cvs.sourceforge.net/viewcvs.py/haskell-libs/libs/crypto/crc32.hs
    --
    -- crc32.hs (C) 2002 HardCore SoftWare, Doug Hoyte
    --
    -- This program is distributed under the terms of the GNU GPL.
    -- See www.gnu.org for more information.
    --
    -- Haskell implementation of the 32-bit Cyclic Redundancy Check.
    -- This code was modeled after the cksum utility distributed with
    -- OpenBSD - the lookup table was in fact lifted from the OpenBSD
    -- implementation.
    --
    -- Once compiled, this program is almost a drop-in replacement for
    -- the OpenBSD cksum utility.

    -- 	$Id: crc32.hs,v 1.2 2003/03/24 00:08:55 eris Exp $

    {- |
       Module     : Data.Hash.CRC32.Posix
       Copyright  : Copyright (C) 2002 HardCore SoftWare, Doug Hoyte
       License    : GNU GPL

       Maintainer : John Goerzen <jgoerzen@complete.org>
       Stability  : provisional
       Portability: portable

    CRC32 checksumming using POSIX 1003.2-1992 algorithm for the polynomial { 32 26
    23 22 16 12 11 10 8 7 5 4 2 1 }, also defined in  ISO 8802-3: 1989.

    Copyright (c) 2002 HardCore SoftWare, Doug Hoyte
    -}

    {-
    Modified December, 2004 by John Goerzen:
     * Integrate with MissingH
     * Removed code we don't need in a library
     * Updated things that didn't compile any more
    -}

    module Data.Hash.CRC32.Posix where

    import Data.Array
    import Data.Bits
    import Data.Word

    iter_crc32       :: Word32 -> Char -> Word32
    iter_crc32 sumval ch = (sumval `shiftL` 8) `xor`
                           crctab ! fromIntegral ((sumval `shiftR` 24) `xor`
                                                  (fromIntegral (fromEnum ch)))

    calc_crc32            :: [Char] -> Word32 -> Word32 -> Word32
    calc_crc32 []     ck 0 = ck `xor` 0xFFFFFFFF
    calc_crc32 []     ck l = calc_crc32
                               []
                               (iter_crc32 ck (toEnum $ fromIntegral (l .&. 0xFF)))
                               (l `shiftR` 8)
    calc_crc32 (x:xs) ck l = calc_crc32 xs (iter_crc32 ck x) (l+1)

    crc32  :: [Char] -> Word32
    crc32 x = calc_crc32 x 0 0

    crctab :: Array Int Word32
    crctab  = array (0,255) (zip [0..255]
             [
             0x0,
             0x04c11db7, 0x09823b6e, 0x0d4326d9, 0x130476dc, 0x17c56b6b,
             0x1a864db2, 0x1e475005, 0x2608edb8, 0x22c9f00f, 0x2f8ad6d6,
             0x2b4bcb61, 0x350c9b64, 0x31cd86d3, 0x3c8ea00a, 0x384fbdbd,
             0x4c11db70, 0x48d0c6c7, 0x4593e01e, 0x4152fda9, 0x5f15adac,
             0x5bd4b01b, 0x569796c2, 0x52568b75, 0x6a1936c8, 0x6ed82b7f,
             0x639b0da6, 0x675a1011, 0x791d4014, 0x7ddc5da3, 0x709f7b7a,
             0x745e66cd, 0x9823b6e0, 0x9ce2ab57, 0x91a18d8e, 0x95609039,
             0x8b27c03c, 0x8fe6dd8b, 0x82a5fb52, 0x8664e6e5, 0xbe2b5b58,
             0xbaea46ef, 0xb7a96036, 0xb3687d81, 0xad2f2d84, 0xa9ee3033,
             0xa4ad16ea, 0xa06c0b5d, 0xd4326d90, 0xd0f37027, 0xddb056fe,
             0xd9714b49, 0xc7361b4c, 0xc3f706fb, 0xceb42022, 0xca753d95,
             0xf23a8028, 0xf6fb9d9f, 0xfbb8bb46, 0xff79a6f1, 0xe13ef6f4,
             0xe5ffeb43, 0xe8bccd9a, 0xec7dd02d, 0x34867077, 0x30476dc0,
             0x3d044b19, 0x39c556ae, 0x278206ab, 0x23431b1c, 0x2e003dc5,
             0x2ac12072, 0x128e9dcf, 0x164f8078, 0x1b0ca6a1, 0x1fcdbb16,
             0x018aeb13, 0x054bf6a4, 0x0808d07d, 0x0cc9cdca, 0x7897ab07,
             0x7c56b6b0, 0x71159069, 0x75d48dde, 0x6b93dddb, 0x6f52c06c,
             0x6211e6b5, 0x66d0fb02, 0x5e9f46bf, 0x5a5e5b08, 0x571d7dd1,
             0x53dc6066, 0x4d9b3063, 0x495a2dd4, 0x44190b0d, 0x40d816ba,
             0xaca5c697, 0xa864db20, 0xa527fdf9, 0xa1e6e04e, 0xbfa1b04b,
             0xbb60adfc, 0xb6238b25, 0xb2e29692, 0x8aad2b2f, 0x8e6c3698,
             0x832f1041, 0x87ee0df6, 0x99a95df3, 0x9d684044, 0x902b669d,
             0x94ea7b2a, 0xe0b41de7, 0xe4750050, 0xe9362689, 0xedf73b3e,
             0xf3b06b3b, 0xf771768c, 0xfa325055, 0xfef34de2, 0xc6bcf05f,
             0xc27dede8, 0xcf3ecb31, 0xcbffd686, 0xd5b88683, 0xd1799b34,
             0xdc3abded, 0xd8fba05a, 0x690ce0ee, 0x6dcdfd59, 0x608edb80,
             0x644fc637, 0x7a089632, 0x7ec98b85, 0x738aad5c, 0x774bb0eb,
             0x4f040d56, 0x4bc510e1, 0x46863638, 0x42472b8f, 0x5c007b8a,
             0x58c1663d, 0x558240e4, 0x51435d53, 0x251d3b9e, 0x21dc2629,
             0x2c9f00f0, 0x285e1d47, 0x36194d42, 0x32d850f5, 0x3f9b762c,
             0x3b5a6b9b, 0x0315d626, 0x07d4cb91, 0x0a97ed48, 0x0e56f0ff,
             0x1011a0fa, 0x14d0bd4d, 0x19939b94, 0x1d528623, 0xf12f560e,
             0xf5ee4bb9, 0xf8ad6d60, 0xfc6c70d7, 0xe22b20d2, 0xe6ea3d65,
             0xeba91bbc, 0xef68060b, 0xd727bbb6, 0xd3e6a601, 0xdea580d8,
             0xda649d6f, 0xc423cd6a, 0xc0e2d0dd, 0xcda1f604, 0xc960ebb3,
             0xbd3e8d7e, 0xb9ff90c9, 0xb4bcb610, 0xb07daba7, 0xae3afba2,
             0xaafbe615, 0xa7b8c0cc, 0xa379dd7b, 0x9b3660c6, 0x9ff77d71,
             0x92b45ba8, 0x9675461f, 0x8832161a, 0x8cf30bad, 0x81b02d74,
             0x857130c3, 0x5d8a9099, 0x594b8d2e, 0x5408abf7, 0x50c9b640,
             0x4e8ee645, 0x4a4ffbf2, 0x470cdd2b, 0x43cdc09c, 0x7b827d21,
             0x7f436096, 0x7200464f, 0x76c15bf8, 0x68860bfd, 0x6c47164a,
             0x61043093, 0x65c52d24, 0x119b4be9, 0x155a565e, 0x18197087,
             0x1cd86d30, 0x029f3d35, 0x065e2082, 0x0b1d065b, 0x0fdc1bec,
             0x3793a651, 0x3352bbe6, 0x3e119d3f, 0x3ad08088, 0x2497d08d,
             0x2056cd3a, 0x2d15ebe3, 0x29d4f654, 0xc5a92679, 0xc1683bce,
             0xcc2b1d17, 0xc8ea00a0, 0xd6ad50a5, 0xd26c4d12, 0xdf2f6bcb,
             0xdbee767c, 0xe3a1cbc1, 0xe760d676, 0xea23f0af, 0xeee2ed18,
             0xf0a5bd1d, 0xf464a0aa, 0xf9278673, 0xfde69bc4, 0x89b8fd09,
             0x8d79e0be, 0x803ac667, 0x84fbdbd0, 0x9abc8bd5, 0x9e7d9662,
             0x933eb0bb, 0x97ffad0c, 0xafb010b1, 0xab710d06, 0xa6322bdf,
             0xa2f33668, 0xbcb4666d, 0xb8757bda, 0xb5365d03, 0xb1f740b4
             ])