Re: g_str_hash

[Karl Nelson <kenelson ece ucdavis edu>]

> 
> Hi,
> 
> g_str_hash is really slow. The Tcl string hash function is twice as
> fast, literally. Here's a test program, and it also shows you the Tcl
> function. Any objections to the Tcl version?

Instead of switching how about just optimizing the one we have a
bit?

guint
copy_of_g_str_hash (gconstpointer v)
{
  const char *s = (char*)v;
  const char *p;
  guint h=0, g;

  for(p = s; *p != '\0'; p += 1) {
    h = ( h << 4 ) + *p;
    if ( ( g = h & 0xf0000000 ) ) {
      h = h ^ (g >> 24);
      h = h ^ g;
    }
  }

  return h /* % M */;
}

=>

guint
copy_of_g_str_hash (gconstpointer v)
{
  const char *s = (char*)v;
  const char *p;
  guint32 h=0;

  for(p = s; *p != '\0' && !(h&0xf0000000); p += 1) {
    h = ( h << 4 ) + *p;
  }
  for(; *p != '\0'; p += 1) {
    h = h ^ ((h >> 24)&0xf0);
    h = ( h << 4 ) + *p;
  }

  return h /* % M */;  
}

This is the exact same hash except operations have been moved to
enhance speed.  The difference being the new one keeps the upper bits 
and thus has less collisions and operates somewhere between the TCL and 
GLib on.  

Also I suggest the << 4 go to << 3 so that you don't create the case
annomally where Aaaaaaaaaaaaa and aaaaaaAaaaaaa are equivent.  (The
shift should be prime to the representation system.

                   -O0  -O3
Original system:   0.54 0.31 
Proposed system:   0.48 0.22 
TCL      system:   0.31 0.12

Is that enough improvement?

--Karl