oz@yunexus.UUCP (Ozan Yigit) (05/22/89)
What I am looking for is a hash function (returning "long") that scrambles
bits very well: a small variation in the string should cause a large
variation in the bits. I thought a hash function like the following
should be able to do this. I am not familiar with CRC polynomials, nor
hash functions based on them. Would someone knowledgeable on the topic
either provide a 32-bit version of this, or send me the appropriate
references on similar, or other bit-scrambling hash functions ??
Please mail. many thnx... oz
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/* [from decus diff]
* Return the CRC16 hash code for the buffer (but never 0).
* Algorithm from Stu Wecker (Digital memo 130-959-002-00).
* Since the value 0 is used as a flag, the hash will be
* 1 if the CRC is 0.
*/
u_long crc16a[] = {
0000000, 0140301, 0140601, 0000500,
0141401, 0001700, 0001200, 0141101,
0143001, 0003300, 0003600, 0143501,
0002400, 0142701, 0142201, 0002100,
};
u_long crc16b[] = {
0000000, 0146001, 0154001, 0012000,
0170001, 0036000, 0024000, 0162001,
0120001, 0066000, 0074000, 0132001,
0050000, 0116001, 0104001, 0043000,
};
u_long
hash(str)
register char *str;
{
register u_long crc;
register u_long tmp;
crc = 0;
while (*str)
tmp = *str++ ^ crc; /* XOR crc with new char */
crc = (crc >> 8)
^ crc16a[(tmp & 0017)]
^ crc16b[(tmp & 0360) >> 4];
}
return ((crc == 0) ? (u_long) 1 : crc);
}
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