Well, since you said you're going to do this thousands of times...

use Inline C =>;

print UniqueCount("0101010101"), "\n";
print UniqueCount("1234567812"), "\n";

__END__
__C__

int UniqueCount(unsigned char *str) {
  char counts[256];
  int i;
  int result;

  /* clear the array */

  for (i = 0; i <= 255; i++) {
    counts[i] = (char) 0;
  }

  /* notice the characters */

  while (*str) {
    counts[*str++] = 1;
  }

  /* now count the results */

  result = 0;
  for (i = 0; i <= 255; i++) {
    result += counts[i];
  }

  return result;
}
[download]

Apologies for my rusty C... I've been coding in Perl too long (however, it worked on the first compile!).

-- Randal L. Schwartz, Perl hacker
Be sure to read my standard disclaimer if this is a reply.