hash_serv.C

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/*===============================<o>=====================================

Copyright 1996, 1997, 2004 Ian Kaplan, Bear Products International,
www.bearcave.com.

All Rights Reserved

You may use this software in software components for which you do
not collect money (e.g., non-commercial software).  All commercial
use is reserved.

===============================<o>=====================================*/

#define NDEBUG 1

#include "sysinc.h"
#include "hash_serv.h"


#define SIZE_INT 4

unsigned int hash_services::str_to_uint( const char *s )
{
    int i, byte_ix, word_cnt;
    char c;
    union {
        unsigned char c[ SIZE_INT ];
        unsigned int  u;
    } val;

    val.u = 0;
    word_cnt = 0;
    for (i = 0, byte_ix = 0; i < strlen( s ); i++, byte_ix = (byte_ix + 1) % SIZE_INT) {
        if (i > 0 && (i % SIZE_INT) == 0) {
            word_cnt++;
        }
        c = s[ i ];
        // Every odd word, shift the character up by one bit
        // It turns out that this makes a big difference in the
        // uniqueness of the key generated from a string
        if (word_cnt & 0x1) {
            c = c << 1;
        }
        val.c[ byte_ix ] ^= c;
    }

  return val.u;
} // str_to_uint

#undef SIZE_INT


unsigned int hash_services::hash_value( const char *name )
{
  unsigned int val, new_val;
  
  val = str_to_uint( name );

  new_val = val ^ (val << 1);
  new_val = new_val ^ (val << 2);
  new_val = new_val ^ (val << 3);
  new_val = new_val ^ (val << 4);
  new_val = new_val ^ (val << 5);
  new_val = new_val ^ (val << 6);
  new_val = new_val ^ (val << 7);
  new_val = new_val ^ (val << 8);
  new_val = new_val ^ (val << 9);
  new_val = new_val ^ (val << 10);
  new_val = new_val ^ (val << 11);
  new_val = new_val ^ (val << 12);
  new_val = new_val ^ (val << 13);
  new_val = new_val ^ (val << 14);
  new_val = new_val ^ (val << 15);
  new_val = new_val ^ (val << 16);

  return new_val;  // adjust for hash table size
} // hash_value

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