smart_str performance

This was a email I sent to Rasmus and another co-worker a while ago and forgot to post the question to the list. I just saw a commit converting zlib to smart_str and figured I would send it now. Comments? Brian ---- I think I found what you were looking for yesterday. implode has change between 4.3 and 4.2. 4.2 does the double pass while 4.3 has changed to use a new smart_str struct with smart_str_appendl function (a struct and function calls around what I was doing in my extension). I decided to run some quick tests and here is what I have found: for ( $i=0; $i < $count; $i++ ) { $arr[] = rand_string_function(); // 12 characters } $start = gettimeofday(); $str = implode( "", $arr ); $end = gettimeofday(); printf( "%8.8d: %8.8f\n", $count, time_diff( $start, $end ) ); give this output: 4.3: 1: 0.00005100 2: 0.00002800 5: 0.00003700 10: 0.00006000 100: 0.00045600 1000: 0.00478600 10000: 0.06507500 100000: 1.71620700 4.2: 1: 0.00004700 2: 0.00002500 5: 0.00002800 10: 0.00004000 100: 0.00022400 1000: 0.00240700 10000: 0.03677200 100000: 0.37068200 While below 10 items I am sure it is hard to tell the difference, but it is slower in all cases. Any clue why one item is slower than two or even five? Brian