Re: Re: Fwd: little request :)

Hi Tjerk, On Mon, Feb 10, 2014 at 7:36 PM, Tjerk Meesters <tjerk.meesters@gmail.com>wrote: > I've given this problem some more thought and the following looked > promising; it would be great to get your feedback on it. > > Basically, to remove the modulo and MAX(), I've used a combined buffer > that's used for the comparison, in two ways: > > 1. PAD := known (padded with \0 based on given_len) > 2. PAD := known CONCAT given > > The comparison is straightforward because we already know the buffer is at > least given_len. > > Implementations of above can be found here: > 1. ¼U\žà¬Â¨éó0œõ > 7https://github.com/datibbaw/php-src/compare/master...const-cmp > 2. > https://github.com/datibbaw/php-src/compare/master...const-cmp-2 > > Bottom line is that this attempts to compromise memory against time > stability. > I think length leak does not matter much. Therefore, I may ignore length leak as it could know it from other codes using strlen(), etc. Our main concern would be performance. https://github.com/yohgaki/php-src/compare/PHP-5.6-rfc-hash-compare and the bench mark result of https://gist.github.com/yohgaki/ede544f290c6cf9fa90d is [yohgaki@dev github-php-src]$ ./php-bin t.php str_siphash_compare Elapsed: 9.450211 Iterations: 1000000 DataSize: 1024 str_xxhash32_compare Elapsed: 3.849933 Iterations: 1000000 DataSize: 1024 str_md5_compare Elapsed: 27.174614 Iterations: 1000000 DataSize: 1024 str_byte_compare Elapsed: 5.874092 Iterations: 1000000 DataSize: 1024 str_byte_compare2 Elapsed: 8.761152 Iterations: 1000000 DataSize: 1024 str_word_compare Elapsed: 1.867914 Iterations: 1000000 DataSize: 1024 str_compare Elapsed: 1.178738 Iterations: 1000000 DataSize: 1024 I had the same idea, but I didn't try as it requires additional memory allocation. str_byte_compare Elapsed: 5.874092 Iterations: 1000000 DataSize: 1024 str_byte_compare2 Elapsed: 8.761152 Iterations: 1000000 DataSize: 1024 1st one is simple byte by byte XOR, 2nd one is using modulo as original patch proposed. There is obvious difference even with additional modulo. str_compare Elapsed: 1.178738 Iterations: 1000000 DataSize: 1024 This is the result of simple strncmp() as a reference. How well your version perform compare to simple strncmp? Regards, -- Yasuo Ohgaki yohgaki@ohgaki.net