| srs5694 | e7b4ff9 | 2009-08-18 13:16:10 -0400 | [diff] [blame^] | 1 | /*
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| 2 | * efone - Distributed internet phone system.
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| 3 | *
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| 4 | * (c) 1999,2000 Krzysztof Dabrowski
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| 5 | * (c) 1999,2000 ElysiuM deeZine
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| 6 | *
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| 7 | * This program is free software; you can redistribute it and/or
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| 8 | * modify it under the terms of the GNU General Public License
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| 9 | * as published by the Free Software Foundation; either version
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| 10 | * 2 of the License, or (at your option) any later version.
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| 11 | *
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| 12 | */
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| 13 |
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| 14 | /* based on implementation by Finn Yannick Jacobs */
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| 15 |
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| 16 | #include <stdio.h>
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| 17 | #include <stdlib.h>
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| 18 |
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| 19 | /* crc_tab[] -- this crcTable is being build by chksum_crc32GenTab().
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| 20 | * so make sure, you call it before using the other
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| 21 | * functions!
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| 22 | */
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| 23 | u_int32_t crc_tab[256];
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| 24 |
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| 25 | /* chksum_crc() -- to a given block, this one calculates the
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| 26 | * crc32-checksum until the length is
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| 27 | * reached. the crc32-checksum will be
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| 28 | * the result.
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| 29 | */
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| 30 | u_int32_t chksum_crc32 (unsigned char *block, unsigned int length)
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| 31 | {
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| 32 | register unsigned long crc;
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| 33 | unsigned long i;
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| 34 |
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| 35 | crc = 0xFFFFFFFF;
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| 36 | for (i = 0; i < length; i++)
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| 37 | {
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| 38 | crc = ((crc >> 8) & 0x00FFFFFF) ^ crc_tab[(crc ^ *block++) & 0xFF];
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| 39 | }
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| 40 | return (crc ^ 0xFFFFFFFF);
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| 41 | }
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| 42 |
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| 43 | /* chksum_crc32gentab() -- to a global crc_tab[256], this one will
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| 44 | * calculate the crcTable for crc32-checksums.
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| 45 | * it is generated to the polynom [..]
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| 46 | */
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| 47 |
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| 48 | void chksum_crc32gentab ()
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| 49 | {
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| 50 | unsigned long crc, poly;
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| 51 | int i, j;
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| 52 |
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| 53 | poly = 0xEDB88320L;
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| 54 | for (i = 0; i < 256; i++)
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| 55 | {
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| 56 | crc = i;
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| 57 | for (j = 8; j > 0; j--)
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| 58 | {
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| 59 | if (crc & 1)
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| 60 | {
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| 61 | crc = (crc >> 1) ^ poly;
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| 62 | }
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| 63 | else
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| 64 | {
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| 65 | crc >>= 1;
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| 66 | }
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| 67 | }
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| 68 | crc_tab[i] = crc;
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| 69 | }
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| 70 | }
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