Archive version of: crc32.r ... version: 1 ... vincentecuye 26-Mar-2006

Amendment note: new script || Publicly available? Yes

REBOL [
    Title: "CRC-32"
    Date: 26-Mar-2006
    Version: 1.0.0
    File: %crc32.r
    Author: "Vincent Ecuyer"
    Purpose: "CRC32 checksum function"
    Usage: {
        Calculates a 32 bits cyclic redundancy code as used
        in gzip/pkzip/etc. Returns a binary.

        >> crc-32 "a string"
        == #{99A255DA}

        >> crc-32 #{112233445566}
        == #{345913D6}
    }
    Comment: {
        Contains a precalculated table for speedup.

        REBOL VM isn't really suited for fast bitwise operations, so this 
        code is quite slow. If the rebcode VM is available, it's used to 
        achieve a more usable speed (between checksum/method 'md5 and
        checksum/method 'sha1 speeds).
    }

    Library: [
        level: 'advanced
        platform: 'all
        type: [module function]
        domain: [math security]
        tested-under: [
            core 2.6.2.3.1 on [Win2K]
            view 1.3.2.3.1 on [Win2K]
            view 1.3.61.3.1 on [Win2K]
            view 1.2.1.1.1 on [AmigaOS30]
            core 2.5.0.1.1 on [AmigaOS30]
        ]
        support: none
        license: 'bsd
        see-also: %rebzip.r
    ]
]
ctx-crc-32: context [
    crc-long: [
                 0   1996959894  -301047508 -1727442502   124634137  1886057615
        -379345611  -1637575261   249268274  2044508324  -522852066 -1747789432
         162941995   2125561021  -407360249 -1866523247   498536548  1789927666
        -205950648  -2067906082   450548861  1843258603  -187386543 -2083289657
         325883990   1684777152   -43845254 -1973040660   335633487  1661365465
         -99664541  -1928851979   997073096  1281953886  -715111964 -1570279054
        1006888145   1258607687  -770865667 -1526024853   901097722  1119000684
        -608450090  -1396901568   853044451  1172266101  -589951537 -1412350631
         651767980   1373503546  -925412992 -1076862698   565507253  1454621731
        -809855591  -1195530993   671266974  1594198024  -972236366 -1324619484
         795835527   1483230225 -1050600021 -1234817731  1994146192    31158534
       -1731059524   -271249366  1907459465   112637215 -1614814043  -390540237
        2013776290    251722036 -1777751922  -519137256  2137656763   141376813
       -1855689577   -429695999  1802195444   476864866 -2056965928  -228458418
        1812370925    453092731 -2113342271  -183516073  1706088902   314042704
       -1950435094    -54949764  1658658271   366619977 -1932296973   -69972891
        1303535960    984961486 -1547960204  -725929758  1256170817  1037604311
       -1529756563   -740887301  1131014506   879679996 -1385723834  -631195440
        1141124467    855842277 -1442165665  -586318647  1342533948   654459306
       -1106571248   -921952122  1466479909   544179635 -1184443383  -832445281
        1591671054    702138776 -1328506846  -942167884  1504918807   783551873
       -1212326853  -1061524307  -306674912 -1698712650    62317068  1957810842
        -355121351  -1647151185    81470997  1943803523  -480048366 -1805370492
         225274430   2053790376  -468791541 -1828061283   167816743  2097651377
        -267414716  -2029476910   503444072  1762050814  -144550051 -2140837941
         426522225   1852507879   -19653770 -1982649376   282753626  1742555852
        -105259153  -1900089351   397917763  1622183637  -690576408 -1580100738
         953729732   1340076626  -776247311 -1497606297  1068828381  1219638859
        -670225446  -1358292148   906185462  1090812512  -547295293 -1469587627
         829329135   1181335161  -882789492 -1134132454   628085408  1382605366
        -871598187  -1156888829   570562233  1426400815  -977650754 -1296233688
         733239954   1555261956 -1026031705 -1244606671   752459403  1541320221
       -1687895376   -328994266  1969922972    40735498 -1677130071  -351390145
        1913087877     83908371 -1782625662  -491226604  2075208622   213261112
       -1831694693   -438977011  2094854071   198958881 -2032938284  -237706686
        1759359992    534414190 -2118248755  -155638181  1873836001   414664567
       -2012718362    -15766928  1711684554   285281116 -1889165569  -127750551
        1634467795    376229701 -1609899400  -686959890  1308918612   956543938
       -1486412191   -799009033  1231636301  1047427035 -1362007478  -640263460
        1088359270    936918000 -1447252397  -558129467  1202900863   817233897
       -1111625188   -893730166  1404277552   615818150 -1160759803  -841546093
        1423857449    601450431 -1285129682 -1000256840  1567103746   711928724
       -1274298825  -1022587231  1510334235   755167117
    ]

    right-shift-8: func [
        "Right-shifts the value by 8 bits and returns it."
        value [integer!] "The value to shift"
    ][
        either negative? value [
            -1 xor value and -256 / 256 xor -1 and 16777215
        ][
            -256 and value / 256
        ]
    ]

    update-crc: func [
        "Returns the data crc."
        data [any-string!] "Data to checksum"
        crc [integer!] "Initial value"
    ][
        foreach char data [
             crc: (right-shift-8 crc) xor pick crc-long crc and 255 xor char + 1
        ]
    ]

    set 'crc-32 either value? 'rebcode [
        rebcode [
            "Returns a CRC32 checksum."
            data [any-string!] "Data to checksum"
        /local char crc i
        ][
            tail? data
            either [
                copy crc #{00000000} -1
            ][
                set crc -1
                until [
                    pick char data 1
                    set.i i crc
                    xor i char
                    and i 255
                    lsr crc 8
                    pickz i crc-long i
                    xor crc i
                    next data
                    tail? data
                ]
                xor crc -1
                do crc [load join "#{" [to-hex crc "}"]]
            ]
            return crc
        ]
    ][
        func [
            "Returns a CRC32 checksum."
            data [any-string!] "Data to checksum"
        ][
            either empty? data [#{00000000}][
                load join "#{" [to-hex -1 xor update-crc data -1 "}"]
            ]
        ]
    ]
]

; Verification
if #{CBF43926} <> crc-32 "123456789" [
    make error! "Test failed - CRC-32 doesn't work with this VM."
]