Message ID | 20231002193311.3985890-1-adhemerval.zanella@linaro.org |
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Use introsort for qsort
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Message
Adhemerval Zanella Netto
Oct. 2, 2023, 7:33 p.m. UTC
The motivation for using introsort is to make it fully AS-safe and AC-Safe, with a limited stack size requirement, to remove the use of malloc (which is troublesome since it seems some programs do longjmp from the callback comparison program), and keep worst-case scenario bounded to O(n*ln(n)) (instead of potentially quadradic as for the quicksort). The implementation does not aim to be the state-of-the-art sort algorithm, instead it uses used a well-understood introsort (used on libstdc++, for instance) and leveraged the current quicksort implementation along with a heapsort one from Linux kernel. Performance-wise, the introsort does fall short compared to the mergesort [1]. I have not added a benchmark because I think this should not be the focus of this patch. Changes from v7: - Move __memswap to a static inline on its own header. - Improve some comments. Changes from v6: - Added internal __memswap symbol. - Improved tst-qsort3 with a reference implementation and a new duplicated input. Changes from v5: - Rewrite heapsort to a custom implementation. - Use may_alias attribute on swap optimization. Changes from v4 - Use enum for swap function selection. - Simplify is_aligned. - Renamed insertsort. Adhemerval Zanella (7): string: Add internal memswap implementation stdlib: Optimization qsort{_r} swap implementation stdlib: Move insertion sort out qsort stdlib: qsort: Move some macros to inline function stdlib: Implement introsort for qsort (BZ 19305) stdlib: Remove use of mergesort on qsort (BZ 21719) stdlib: Add more qsort{_r} coverage include/stdlib.h | 2 - include/string.h | 3 + manual/argp.texi | 2 +- manual/locale.texi | 3 +- manual/search.texi | 7 +- stdlib/Makefile | 3 +- stdlib/msort.c | 309 ----------------------------------- stdlib/qsort.c | 315 +++++++++++++++++++++++++++--------- stdlib/tst-qsort3.c | 366 ++++++++++++++++++++++++++++++++++++++++++ string/Makefile | 13 ++ string/memswap.c | 41 +++++ string/test-memswap.c | 191 ++++++++++++++++++++++ 12 files changed, 856 insertions(+), 399 deletions(-) delete mode 100644 stdlib/msort.c create mode 100644 stdlib/tst-qsort3.c create mode 100644 string/memswap.c create mode 100644 string/test-memswap.c