[PATCH][libstdc++-v3 parallel mode] Improve find algorithm

[Johannes Singler]

This patch improves the parallel find algorithm by making the block size
proportional to the current start position, which gives nice theoretical
performance guarantees and better performance in practice.

Tested x86_64-unknown-linux-gnu: No regressions

Please approve for mainline.

2010-06-08  Johannes Singler  <singler@kit.edu>

        * include/parallel/find.h
        (__find_template(.., growing_blocks_tag)): Make block size
        proportional to current position.
        * include/parallel/settings.h (_Settings): Introduce new tuning
        parameter find_scale_factor to the end of the struct, default to
        0.01.

Johannes


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