Re: Unicode string iterator performance

Hi Andrei,

Pardon me for my ignorance, as I have not even looked at the Unicode 
stuff, but based on what you wrote, what about always allocating two 
UChars per codepoint? It would take a bit more space, but then 
random-offset indexing is fast and easy (the codepoint would always 
start at "index << 1").


Regards,

Jessie Hernandez


Andrei Zmievski wrote:
> You probably saw that I have committed initial implementation of 
> TextIterator. The impetus for this is that direct indexing of Unicode 
> strings via [] operator is slow, very slow, at least currently. The 
> reason is that [] cannot simply perform random-offset indexing into 
> UCHar* strings. It needs to start from the beginning of the string and 
> iterate forward until it reaches the desired offset, because our default 
> unit is a codepoint, which can take up 1 or 2 UChar's.
> 
> So here are some (rough) numbers on the relative performance of 
> TextIterator vs. []. The script I used was a simple one (attached after 
> the signature). Each test was 10000 runs over 500-character string.
> 
> [] operator:  27.16373 s
> TextIterator: 1.89697 s (!)
> 
> For comparison, running the same [] operator test on a 500-character 
> binary (old-style) string gives me 9.11334 s. Quite interesting, I'd say.
> 
> I am not sure how we can optimize [] to be faster than the iterator 
> approach. Food for thought?
> 
> - Andrei
> 
> <?php
> $a = str_repeat('a\U010201bcß', 100);
> var_dump($a);
> 
> /* warm up the engine */
> for ($x = 0; $x < 100; $x++) {
> foreach (new TextIterator($a) as $c) {
> }
> }
> 
> /* measure [] */
> $start = microtime(true);
> for ($x = 0; $x < 10000; $x++) {
>     $len = strlen($a);
>     for ($i = 0; $i < $len; $i++) {
>         $c = $a[$i];
>     }
> }
> $end = microtime(true);
> 
> printf("[] run time: %.5f\n", $end - $start);
> 
> /* measure iterator */
> $start = microtime(true);
> for ($x = 0; $x < 10000; $x++) {
> foreach (new TextIterator($a) as $c) {
> }
> }
> $end = microtime(true);
> 
> printf("iterator run time: %.5f\n", $end - $start);
> ?>