[Issue 21559] New: Speed up walkLength for narrow strings

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21559

          Issue ID: 21559
           Summary: Speed up walkLength for narrow strings
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: n8sh.secondary at hotmail.com

walkLength can be significantly sped up for narrow strings in the common case
where they begin with a run of characters that do not require decoding.

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