[bug #68174] dlmread performance can be improved with modern C++

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URL:
  <https://savannah.gnu.org/bugs/?68174>

                 Summary: dlmread performance can be improved with modern C++
                   Group: GNU Octave
               Submitter: dasergatskov
               Submitted: Wed 25 Mar 2026 02:35:49 AM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Performance
                  Status: None
             Assigned to: None
         Originator Name:
        Originator Email:
             Open/Closed: Open
         Discussion Lock: Unlocked
                 Release: dev
        Operating System: Any
           Fixed Release: None
         Planned Release: None


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Follow-up Comments:


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Date: Wed 25 Mar 2026 02:35:49 AM UTC By: Dmitri A. Sergatskov <dasergatskov>
While working on bug #68167 I noticed that the inner loop in the parser (in
dlmread) uses very expensive things: "std::string str = line.substr (...)"
creates a new std::string object which may trigger heap alloc/dealloc. 
std::istringstream is notoriously slow: see e.g.:
https://stackoverflow.com/questions/5830868/c-stringstream-is-too-slow-how-to-speed-up

I think the performance could be improved by using allocation-free
"string_view" and "from_chars" for numbers parsing. 

I should be able to make a CSET soon.

Dmitri.
-- 








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