psyclpc/src/hash.c

/*---------------------------------------------------------------------------
 * String Hashing Functions
 *
 *---------------------------------------------------------------------------
 * A simple and fast generic string hasher based on Peter K. Pearson's
 * article in Communications of the ACM 33-6, pp. 677.
 * TODO: Use Bob Jenkins hash instead of Pearson's?
 *---------------------------------------------------------------------------
 */

#include <stdlib.h>

#include "hash.h"

/*-------------------------------------------------------------------------*/
static unsigned char T[]
 = {
          1,  87,  49,  12, 176, 178, 102, 166,
        121, 193,   6,  84, 249, 230,  44, 163,
         14, 197, 213, 181, 161,  85, 218,  80,
         64, 239,  24, 226, 236, 142,  38, 200,
        110, 177, 104, 103, 141, 253, 255,  50,
         77, 101,  81,  18,  45,  96,  31, 222,
         25, 107, 190,  70,  86, 237, 240,  34,
         72, 242,  20, 214, 244, 227, 149, 235,
         97, 234,  57,  22,  60, 250,  82, 175,
        208,   5, 127, 199, 111,  62, 135, 248,
        174, 169, 211,  58,  66, 154, 106, 195,
        245, 171,  17, 187, 182, 179,   0, 243,
        132,  56, 148,  75, 128, 133, 158, 100,
        130, 126,  91,  13, 153, 246, 216, 219,
        119,  68, 223,  78,  83,  88, 201,  99,
        122,  11,  92,  32, 136, 114,  52,  10,
        138,  30,  48, 183, 156,  35,  61,  26,
        143,  74, 251,  94, 129, 162,  63, 152,
        170,   7, 115, 167, 241, 206,   3, 150,
         55,  59, 151, 220,  90,  53,  23, 131,
        125, 173,  15, 238,  79,  95,  89,  16,
        105, 137, 225, 224, 217, 160,  37, 123,
        118,  73,   2, 157,  46, 116,   9, 145,
        134, 228, 207, 212, 202, 215,  69, 229,
         27, 188,  67, 124, 168, 252,  42,   4,
         29, 108,  21, 247,  19, 205,  39, 203,
        233,  40, 186, 147, 198, 192, 155,  33,
        164, 191,  98, 204, 165, 180, 117,  76,
        140,  36, 210, 172,  41,  54, 159,   8,
        185, 232, 113, 196, 231,  47, 146, 120,
         51,  65,  28, 144, 254, 221,  93, 189,
        194, 139, 112,  43,  71, 109, 184, 209,
 };

/*-------------------------------------------------------------------------*/
whash_t
whashmem (const char *s, size_t len, int maxn)

/* Hash the first min(<len>,<maxn>) characters of string <s> into a short
 * integer and return this hashed value.
 */

{
    register chash_t hi, lo;
    register unsigned char c;
    register unsigned char *p = (unsigned char *)s;
    register size_t i = maxn;

    if (i > len)
        i = len;

    if ( i > 0 )
    {
        c = *p++;
        for (hi = T[c], lo = (unsigned char)(c + 1)
            ; --i > 0; )
        {
            c = *p++;
            hi = T[hi ^ c];
            lo = T[lo ^ c];
        }
        return (whash_t)((hi << 8) + lo);
    }
    return 0;
} /* whashmem() */

/*-------------------------------------------------------------------------*/
whash_t
whashmem2 (const char *s, size_t len, int maxn, whash_t initial)

/* Hash the first min(<len>,<maxn>) characters of string <s> into a short
 * integer and return this hashed value.
 * The hash value is initialized with <initial>, so that this function
 * can be used to hash a series of strings into one result.
 */

{
    register chash_t hi, lo;
    register unsigned char c;
    register unsigned char *p = (unsigned char *)s;
    register size_t i = maxn;

    hi = (initial >> 8) & 0xFF;
    lo = initial & 0xFF;

    if (i > len)
        i = len;

    if ( i > 0 )
    {
        for ( ; --i > 0; )
        {
            c = *p++;
            hi = T[hi ^ c];
            lo = T[lo ^ c];
        }
        return (whash_t)((hi << 8) + lo);
    }
    return 0;
} /* whashmem2() */

/*-------------------------------------------------------------------------*/
whash_t
whashstr (const char *s, int maxn)

/* Hash the first <maxn> characters of string <s> into a short integer and
 * return this hashed value.
 */

{
    register chash_t hi, lo;
    register unsigned char c;
    register unsigned char *p = (unsigned char *)s;
    register long i = maxn;

    if ( i > 0 && '\0' != (c = *p++) )
    {
        for (hi = T[c], lo = (unsigned char)(c + 1)
            ; --i > 0 && '\0' != (c = *p++); )
        {
            hi = T[hi ^ c];
            lo = T[lo ^ c];
        }
        return (whash_t)((hi << 8) + lo);
    }
    return 0;
} /* whashstr() */

/*-------------------------------------------------------------------------*/
chash_t
chashstr (const char *s, int maxn)

/* Hash the first <maxn> characters of string <s> into a char-sized integer
 * and return this hashed value.
 * This function is less precise, but also faster than whashstr().
 */

{
    register chash_t h;
    register unsigned char *p;
    register long i;
    for (h = 0, i = maxn, p = (unsigned char *)s; *p && --i >= 0; p++)
        h = T[h ^ *p];
    return h;
} /* chashstr() */

/***************************************************************************/