Re: Does anyone have a better scm_string_hash ?

[Marius Vollmer <mvo@zagadka.de>]

Roland Orre <orre@nada.kth.se> writes:

> /* replaced by Roland Orre orre@nada.kth.se */
> #define hash_mask 0x00FFFFFF
> unsigned long 
> scm_string_hash (const unsigned char *str, size_t len)
> {
>   /* from suggestion at: */
>   /* http://srfi.schemers.org/srfi-13/mail-archive/msg00112.html */
>   int i;
>   /* originally h=0 was suggested. orre@nada.kth.se */
>   unsigned long h=177;
>
>   for (i = len-1; i >= 0; i--)
>     {
>       /* h = (str[i] +i+ h*37) & hash_mask; */
>       h = (str[i] + i + (h<<5) + (h<<2) + h) & hash_mask;
>     }
>   return h;
> } /* scm_string_hash */

g_string_hash from glib uses the same approach, but with 31 instead of
37 and with a h=0 seed:

    /* 31 bit hash function */
    guint
    g_str_hash (gconstpointer key)
    {
      const char *p = key;
      guint h = *p;

      if (h)
        for (p += 1; *p != '\0'; p++)
          h = (h << 5) - h + *p;

      return h;
    }

So which one is it? :)

Both should be much better than the one we have right now and I'm
going to install the one from Roland without the hash_mask.

OK?

-- 
GPG: D5D4E405 - 2F9B BCCC 8527 692A 04E3  331E FAF8 226A D5D4 E405


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