/*
**  Str - String Library
**  Copyright (c) 1999-2001 Ralf S. Engelschall <rse@engelschall.com>
**
**  This file is part of Str, a string handling and manipulation 
**  library which can be found at http://www.engelschall.com/sw/str/.
**
**  Permission to use, copy, modify, and distribute this software for
**  any purpose with or without fee is hereby granted, provided that
**  the above copyright notice and this permission notice appear in all
**  copies.
**
**  THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
**  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
**  MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
**  IN NO EVENT SHALL THE AUTHORS AND COPYRIGHT HOLDERS AND THEIR
**  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
**  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
**  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
**  USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
**  ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
**  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
**  OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
**  SUCH DAMAGE.
**
**  str_hash.c: hashing functions 
*/

#include "str_p.h"

/*
 * DJBX33A (Daniel J. Bernstein, Times 33 with Addition)
 *
 * This is Daniel J. Bernstein's popular `times 33' hash function as
 * posted by him years ago on comp.lang.c. It basically uses a function
 * like ``hash(i) = hash(i-1) * 33 + string[i]''. This is one of the
 * best hashing functions for strings. Because it is both computed very
 * fast and distributes very well.
 *
 * The magic of the number 33, i.e. why it works better than many other
 * constants, prime or not, has never been adequately explained by
 * anyone. So I try an own RSE-explanation: if one experimentally tests
 * all multipliers between 1 and 256 (as I did it) one detects that
 * even numbers are not useable at all. The remaining 128 odd numbers
 * (except for the number 1) work more or less all equally well. They
 * all distribute in an acceptable way and this way fill a hash table
 * with an average percent of approx. 86%. 
 *
 * If one compares the Chi/2 values resulting of the various
 * multipliers, the 33 not even has the best value. But the 33 and a
 * few other equally good values like 17, 31, 63, 127 and 129 have
 * nevertheless a great advantage over the remaining values in the large
 * set of possible multipliers: their multiply operation can be replaced
 * by a faster operation based on just one bit-wise shift plus either a
 * single addition or subtraction operation. And because a hash function
 * has to both distribute good and has to be very fast to compute, those
 * few values should be preferred and seems to be also the reason why
 * Daniel J. Bernstein also preferred it.
 */
static unsigned long 
hash_djbx33(
    register unsigned char *key, 
    register str_size_t len)
{
    register unsigned long hash = 5381;

    /* the hash unrolled eight times */
    for (; len >= 8; len -= 8) {
        hash = ((hash << 5) + hash) + *key++;
        hash = ((hash << 5) + hash) + *key++;
        hash = ((hash << 5) + hash) + *key++;
        hash = ((hash << 5) + hash) + *key++;
        hash = ((hash << 5) + hash) + *key++;
        hash = ((hash << 5) + hash) + *key++;
        hash = ((hash << 5) + hash) + *key++;
        hash = ((hash << 5) + hash) + *key++;
    }
    switch (len) {
        case 7: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
        case 6: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
        case 5: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
        case 4: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
        case 3: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
        case 2: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
        case 1: hash = ((hash << 5) + hash) + *key++; break;
        default: /* case 0: */ break;
    }
    return hash;
}

/*
 * BJDDJ (Bob Jenkins, Dr. Dobbs Journal)
 *
 * This is a very complex but also very good hashing function, as
 * proposed in the March'97 issue of Dr. Dobbs Journal (DDJ) by Bob
 * Jenkins (see http://burtleburtle.net/bob/hash/doobs.html for online
 * version). He showed in his texts, that his hash function has both
 * very good distribution and performance and my own hash function
 * comparison confirmed this, too. The only difference to the original
 * function of B.J. here is that my version doesn't provide the `level'
 * (= previous hash) argument for consistency reasons with the other
 * hash functions (i.e. same function signature). It can be definitely
 * recommended as a very good general purpose hashing function.
 */
static unsigned long 
hash_bjddj(
    register unsigned char *k,
    register str_size_t length)
{
    register unsigned long a,b,c,len;

    /* some abbreviations */
#define ub4 unsigned long
#define mix(a,b,c) { \
        a -= b; a -= c; a ^= (c>>13); \
        b -= c; b -= a; b ^= (a<< 8); \
        c -= a; c -= b; c ^= (b>>13); \
        a -= b; a -= c; a ^= (c>>12); \
        b -= c; b -= a; b ^= (a<<16); \
        c -= a; c -= b; c ^= (b>> 5); \
        a -= b; a -= c; a ^= (c>> 3); \
        b -= c; b -= a; b ^= (a<<10); \
        c -= a; c -= b; c ^= (b>>15); \
    }

    /* setup the internal state */
    len = length;
    a = b = 0x9e3779b9;  /* the golden ratio; an arbitrary value */
    c = 0;

    /* handle most of the key */
    while (len >= 12) {
        a += (k[0] +((ub4)k[1]<<8) +((ub4)k[ 2]<<16) +((ub4)k[ 3]<<24));
        b += (k[4] +((ub4)k[5]<<8) +((ub4)k[ 6]<<16) +((ub4)k[ 7]<<24));
        c += (k[8] +((ub4)k[9]<<8) +((ub4)k[10]<<16) +((ub4)k[11]<<24));
        mix(a,b,c);
        k += 12; len -= 12;
    }

    /* handle the last 11 bytes */
    c += length;
    switch(len) { 
        /* all the case statements fall through */
        case 11: c += ((ub4)k[10]<<24);
        case 10: c += ((ub4)k[ 9]<<16);
        case 9 : c += ((ub4)k[ 8]<< 8);
        /* the first byte of c is reserved for the length */
        case 8 : b += ((ub4)k[ 7]<<24);
        case 7 : b += ((ub4)k[ 6]<<16);
        case 6 : b += ((ub4)k[ 5]<< 8);
        case 5 : b += k[4];
        case 4 : a += ((ub4)k[ 3]<<24);
        case 3 : a += ((ub4)k[ 2]<<16);
        case 2 : a += ((ub4)k[ 1]<< 8);
        case 1 : a += k[0];
        /* case 0: nothing left to add */
    }
    mix(a,b,c);

    /* delete abbreviations */
#undef ub4
#undef mix

    /* report the result */
    return c;
}

/*
 * MACRC32 (Mark Adler, Cyclic Redundancy Check 32-Bit)
 *
 * This hash function is based on the good old CRC-32 (Cyclic Redundancy
 * Check with 32 Bit) algorithm as invented by Mark Adler. It is one
 * of the hash functions with medium performance but with very good
 * distribution. So it can be considered as a rock solid general purpose
 * hash function. It should be used if good distribution is more
 * important than high performance.
 */
static unsigned long 
hash_macrc32(
    register unsigned char *key,
    register str_size_t len)
{
    /* the CRC-32 table */
    static unsigned long tab[256] = {
        0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL, 0x076dc419L,
        0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0x0edb8832L, 0x79dcb8a4L,
        0xe0d5e91eL, 0x97d2d988L, 0x09b64c2bL, 0x7eb17cbdL, 0xe7b82d07L,
        0x90bf1d91L, 0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL,
        0x1adad47dL, 0x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L, 0x136c9856L,
        0x646ba8c0L, 0xfd62f97aL, 0x8a65c9ecL, 0x14015c4fL, 0x63066cd9L,
        0xfa0f3d63L, 0x8d080df5L, 0x3b6e20c8L, 0x4c69105eL, 0xd56041e4L,
        0xa2677172L, 0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL, 0xa50ab56bL,
        0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L, 0x32d86ce3L,
        0x45df5c75L, 0xdcd60dcfL, 0xabd13d59L, 0x26d930acL, 0x51de003aL,
        0xc8d75180L, 0xbfd06116L, 0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L,
        0xb8bda50fL, 0x2802b89eL, 0x5f058808L, 0xc60cd9b2L, 0xb10be924L,
        0x2f6f7c87L, 0x58684c11L, 0xc1611dabL, 0xb6662d3dL, 0x76dc4190L,
        0x01db7106L, 0x98d220bcL, 0xefd5102aL, 0x71b18589L, 0x06b6b51fL,
        0x9fbfe4a5L, 0xe8b8d433L, 0x7807c9a2L, 0x0f00f934L, 0x9609a88eL,
        0xe10e9818L, 0x7f6a0dbbL, 0x086d3d2dL, 0x91646c97L, 0xe6635c01L,
        0x6b6b51f4L, 0x1c6c6162L, 0x856530d8L, 0xf262004eL, 0x6c0695edL,
        0x1b01a57bL, 0x8208f4c1L, 0xf50fc457L, 0x65b0d9c6L, 0x12b7e950L,
        0x8bbeb8eaL, 0xfcb9887cL, 0x62dd1ddfL, 0x15da2d49L, 0x8cd37cf3L,
        0xfbd44c65L, 0x4db26158L, 0x3ab551ceL, 0xa3bc0074L, 0xd4bb30e2L,
        0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL, 0x4369e96aL,
        0x346ed9fcL, 0xad678846L, 0xda60b8d0L, 0x44042d73L, 0x33031de5L,
        0xaa0a4c5fL, 0xdd0d7cc9L, 0x5005713cL, 0x270241aaL, 0xbe0b1010L,
        0xc90c2086L, 0x5768b525L, 0x206f85b3L, 0xb966d409L, 0xce61e49fL,
        0x5edef90eL, 0x29d9c998L, 0xb0d09822L, 0xc7d7a8b4L, 0x59b33d17L,
        0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL, 0xedb88320L, 0x9abfb3b6L,
        0x03b6e20cL, 0x74b1d29aL, 0xead54739L, 0x9dd277afL, 0x04db2615L,
        0x73dc1683L, 0xe3630b12L, 0x94643b84L, 0x0d6d6a3eL, 0x7a6a5aa8L,
        0xe40ecf0bL, 0x9309ff9dL, 0x0a00ae27L, 0x7d079eb1L, 0xf00f9344L,
        0x8708a3d2L, 0x1e01f268L, 0x6906c2feL, 0xf762575dL, 0x806567cbL,
        0x196c3671L, 0x6e6b06e7L, 0xfed41b76L, 0x89d32be0L, 0x10da7a5aL,
        0x67dd4accL, 0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L, 0x60b08ed5L,
        0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L, 0xd1bb67f1L,
        0xa6bc5767L, 0x3fb506ddL, 0x48b2364bL, 0xd80d2bdaL, 0xaf0a1b4cL,
        0x36034af6L, 0x41047a60L, 0xdf60efc3L, 0xa867df55L, 0x316e8eefL,
        0x4669be79L, 0xcb61b38cL, 0xbc66831aL, 0x256fd2a0L, 0x5268e236L,
        0xcc0c7795L, 0xbb0b4703L, 0x220216b9L, 0x5505262fL, 0xc5ba3bbeL,
        0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L, 0xc2d7ffa7L, 0xb5d0cf31L,
        0x2cd99e8bL, 0x5bdeae1dL, 0x9b64c2b0L, 0xec63f226L, 0x756aa39cL,
        0x026d930aL, 0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x05005713L,
        0x95bf4a82L, 0xe2b87a14L, 0x7bb12baeL, 0x0cb61b38L, 0x92d28e9bL,
        0xe5d5be0dL, 0x7cdcefb7L, 0x0bdbdf21L, 0x86d3d2d4L, 0xf1d4e242L,
        0x68ddb3f8L, 0x1fda836eL, 0x81be16cdL, 0xf6b9265bL, 0x6fb077e1L,
        0x18b74777L, 0x88085ae6L, 0xff0f6a70L, 0x66063bcaL, 0x11010b5cL,
        0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L, 0xa00ae278L,
        0xd70dd2eeL, 0x4e048354L, 0x3903b3c2L, 0xa7672661L, 0xd06016f7L,
        0x4969474dL, 0x3e6e77dbL, 0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L,
        0x37d83bf0L, 0xa9bcae53L, 0xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L,
        0xbdbdf21cL, 0xcabac28aL, 0x53b39330L, 0x24b4a3a6L, 0xbad03605L,
        0xcdd70693L, 0x54de5729L, 0x23d967bfL, 0xb3667a2eL, 0xc4614ab8L,
        0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL,
        0x2d02ef8dL
    };
    register unsigned long hash;
    
    /* compute hash with the help of the table */
    hash = 0xffffffff;
    while (len-- > 0)
        hash = tab[(hash ^ *key++) & 0xff] ^ (hash >> 8);
    hash ^= 0xffffffff;

    /* return the calculated hash value */
    return hash;
}

/*
 * The API function.
 */
unsigned long 
str_hash(
    const char *s, 
    str_size_t n, 
    int mode)
{
    unsigned long hash;

    if (s == NULL)
        return 0;
    if (n == 0)
        n = str_len(s);
    switch (mode) {
        case STR_HASH_DJBX33:
            hash = hash_djbx33((unsigned char *)s, n);
            break;
        case STR_HASH_BJDDJ:
            hash = hash_bjddj((unsigned char *)s, n);
            break;
        case STR_HASH_MACRC32:
            hash = hash_macrc32((unsigned char *)s, n);
            break;
        default:
            hash = 0;
            break;
    }
    return hash;
}

