Doc #73913 [Com]: broken strrpos with negative offset

Edit report at https://bugs.php.net/bug.php?id=73913&edit=1 ID: 73913 Comment by: dima at virtuman dot com Reported by: proartex at mail dot ru Summary: broken strrpos with negative offset Status: Assigned Type: Documentation Problem Package: Strings related Operating System: macOS Sierra 10.12.1 PHP Version: 5.6.29 Assigned To: heiglandreas Block user comment: N Private report: N New Comment: Java implementation has no negative fromIndex for "public int lastIndexOf(String str, int fromIndex)". Java implementation returns "-1" for any negative fromIndex. There is an examples from python: " >>> 'aaaa'.rfind('a',0, -2) 1 >>> 'aaaa'.rfind('a', 0, -1) 2 >>> '/documents/show/5474'.rfind('/', 0, -20) -1 >>> 'works_like_a_charm'.rfind('charm', 0, -3) -1 >>> 'works_like_a_charm'.rfind('charm', 0, -5) -1 " It works the way we expect Previous Comments: ------------------------------------------------------------------------ [2017-01-13 15:48:10] heiglandreas@php.net For more infos have a look at https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#lastIndexOf(java.lang.String,%20int) ------------------------------------------------------------------------ [2017-01-13 15:46:33] heiglandreas@php.net The current implementation is mathematically correct and is the same as f.e. the implementation in Java and other programming languages. The docs are misleading here. The negative offset specifies the last offset in the string the needle can start. Therefore the results are correct. Though the documentation of that feature needs some work to explicitly state that and make that more clear. ------------------------------------------------------------------------ [2017-01-12 11:30:39] dima at virtuman dot com my previous comment is not absolutely right. I'm not sure why those conditions are needed: if (needle_len > -offset) { e = haystack + haystack_len - needle_len; } else { e = haystack + haystack_len + offset; } In all cases we need to subtract absolute value of offset from e pointer and also subtract value of needle length. There is no reason to check needle_len > -offset ------------------------------------------------------------------------ [2017-01-12 10:33:07] dima at virtuman dot com Looks like the problem is related to https://github.com/php/php-src/blob/PHP-5.6.29/ext/standard/string.c#L1987 replace this one: e = haystack + haystack_len + offset; with this one: e = haystack + haystack_len + offset - needle_len; will solve the problem. ------------------------------------------------------------------------ [2017-01-11 21:57:27] heiglandreas@php.net Looks like you're right! I dug deeper into it and it seems there is an issue when the negative offset is smaller or equals the size of the needle. I'm digging deeper into it. ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at https://bugs.php.net/bug.php?id=73913 -- Edit this bug report at https://bugs.php.net/bug.php?id=73913&edit=1