Add a move_to function to cudf::string_view::const_iterator #13428
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…ings (#13322) Changes the internal regex logic to minimize character counting to help performance with longer strings. The improvement applies mainly to libcudf regex functions that return strings (i.e. extract, replace, split). The changes here also improve the internal device APIs for clarity to improve maintenance. The most significant change makes the position variables input-only and returning an optional pair to indicate a successful match. There are some more optimizations that are possible here where character positions are passed back and forth that could be replaced with byte positions to further reduce counting. Initial measurements showed this noticeably slowed down small strings so more analysis is required before continuing this optimization. Reference: #13480 ### More Detail First, there is a change to some internal regex function signatures. Notable the `reprog_device::find()` and `reprog_device::extract()` member functions declared in `cpp/src/strings/regex/regex.cuh` that are used by all the libcudf regex functions. The in/out parameters are now input-only parameters (pass by value) and the return is an optional pair that includes the match result. Also, the `begin` parameter is now an iterator and the `end` parameter now has a default. This change requires updating all the definitions and uses of the `find` and `extract` member functions. Using an iterator as the `begin` parameter allows for some optimizations in the calling code to minimize character counting that may be needed for processing multi-byte UTF-8 characters. Rather than using the `cudf::string_view::byte_offset()` member function to convert character positions to byte positions, an iterator can be incremented as we traverse through the string which helps reduce some character counting. So the changes here involve removing some calls to `byte_offset()` and incrementing (really moving) iterators with a pattern like `itr += (new_pos - itr.position());` There is another PR #13428 to make a `move_to` iterator member function. It is possible to reduce the character counting even more as mentioned above but further optimization requires some deeper analysis. Authors: - David Wendt (https://github.com/davidwendt) Approvers: - Mark Harris (https://github.com/harrism) - MithunR (https://github.com/mythrocks) URL: #13322
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Description
Adds a
move_to()function thecudf::string_view::const_iteratorclass to help minimize character counting when creating and incrementing the iterator on multi-byte UTF8 characters.The function simply moves the iterator from the current character position to the given one. This is just a shortcut for the form
This pattern is repeated many times in #13322 and likely future PRs that require the same behavior.
The PR also includes an update to the
string_view::begin()to set the byte-offset directly rather than waste instructions calculating it.Checklist