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Re: [PATCH v2 3/6] match_basename: use strncmp instead of strcmp

From
Junio C Hamano <gitster@pobox.com>
Date
Mar 12, 2013, 20:59 UTC
Message-ID
<7v7glc72rn.fsf@alter.siamese.dyndns.org>
In-Reply-To
<CACsJy8A_4SqLu5L6P0PJ78Lwy12fjL7T2p-KbVEVLJmKNqhyRw@mail.gmail.com>
Duy Nguyen <pclouds@gmail.com> writes:
Show 5 quoted lines
> glibc's C strncmp version does 4-byte comparison at a time when n >=4,
> then fall back to 1-byte for the rest. I don't know if it's faster
> than a plain always 1-byte comparison though. There's also the hand
> written assembly version that compares n from 1..16, not exactly sure
> how this version works yet.

It sounds to me more like "a very popular implementation of strcmp/strncmp pair found to have more optimized strncmp than strcmp". While that may be a good reason to justify this patch, I do not think it justifies this:

>> strncmp is provided length information which could be taken advantage
>> by the underlying implementation.

After all, strcmp() could also be optimized to fetch word-at-a-time while being careful about not overstepping the page boundary.

Previous: Duy NguyenNext: Duy Nguyen
Message 20 of 48 in “Trivial (and small) exclude optimizations”
  1. 0/3 Trivial (and small) exclude optimizationsNguyễn Thái Ngọc Duy, Mar 9, 2013
  2. 1/3 match_pathname: avoid calling strncmp if baselen is 0Nguyễn Thái Ngọc Duy, Mar 9, 2013
  3. Antoine PelisseMar 9, 2013
  4. 2/3 dir.c: inline convenient *_icase helpersNguyễn Thái Ngọc Duy, Mar 9, 2013
  5. 3/3 match_basename: use strncmp instead of strcmpNguyễn Thái Ngọc Duy, Mar 9, 2013
  6. Junio C HamanoMar 9, 2013
  7. Fredrik GustafssonMar 9, 2013
  8. Duy NguyenMar 9, 2013
  9. 0/6 Exclude optimizationsNguyễn Thái Ngọc Duy, Mar 10, 2013
  10. 1/6 match_pathname: avoid calling strncmp if baselen is 0Nguyễn Thái Ngọc Duy, Mar 10, 2013
  11. 2/6 dir.c: inline convenient *_icase helpersNguyễn Thái Ngọc Duy, Mar 10, 2013
  12. 3/6 match_basename: use strncmp instead of strcmpNguyễn Thái Ngọc Duy, Mar 10, 2013
  13. Junio C HamanoMar 10, 2013
  14. Duy NguyenMar 10, 2013
  15. Antoine PelisseMar 10, 2013
  16. Antoine PelisseMar 10, 2013
  17. Duy NguyenMar 10, 2013
  18. Antoine PelisseMar 10, 2013
  19. Duy NguyenMar 10, 2013
  20. Junio C HamanoMar 12, 2013
  21. Duy NguyenMar 13, 2013
  22. 4/6 match_{base,path}name: replace strncmp_icase with strnequal_icaseNguyễn Thái Ngọc Duy, Mar 10, 2013
  23. 5/6 dir.c: pass pathname length to last_exclude_matchingNguyễn Thái Ngọc Duy, Mar 10, 2013
  24. 6/6 exclude: filter patterns by directory levelNguyễn Thái Ngọc Duy, Mar 10, 2013
  25. Junio C HamanoMar 10, 2013
  26. Duy NguyenMar 10, 2013
  27. Junio C HamanoMar 10, 2013
  28. Duy NguyenMar 10, 2013
  29. Duy NguyenMar 11, 2013
  30. 00/13 Exclude optimizationsNguyễn Thái Ngọc Duy, Mar 12, 2013
  31. 01/13 dir.c: add MEASURE_EXCLUDE code for tracking exclude performanceNguyễn Thái Ngọc Duy, Mar 12, 2013
  32. 02/13 match_pathname: avoid calling strncmp if baselen is 0Nguyễn Thái Ngọc Duy, Mar 12, 2013
  33. 03/13 dir.c: inline convenient *_icase helpersNguyễn Thái Ngọc Duy, Mar 12, 2013
  34. 04/13 match_basename: use strncmp instead of strcmpNguyễn Thái Ngọc Duy, Mar 12, 2013
  35. Antoine PelisseMar 12, 2013
  36. Duy NguyenMar 13, 2013
  37. 05/13 match_{base,path}name: replace strncmp_icase with memequal_icaseNguyễn Thái Ngọc Duy, Mar 12, 2013
  38. Duy NguyenMar 13, 2013
  39. 06/13 dir: pass pathname length to last_exclude_matchingNguyễn Thái Ngọc Duy, Mar 12, 2013
  40. 07/13 exclude: avoid calling prep_exclude on entries of the same directoryNguyễn Thái Ngọc Duy, Mar 12, 2013
  41. 08/13 exclude: record baselen in the patternNguyễn Thái Ngọc Duy, Mar 12, 2013
  42. 09/13 exclude: filter out patterns not applicable to the current directoryNguyễn Thái Ngọc Duy, Mar 12, 2013
  43. Eric SunshineMar 12, 2013
  44. 10/13 read_directory: avoid invoking exclude machinery on tracked filesNguyễn Thái Ngọc Duy, Mar 12, 2013
  45. 11/13 Preallocate hash tables when the number of inserts are known in advanceNguyễn Thái Ngọc Duy, Mar 12, 2013
  46. 12/13 name-hash: allow to lookup a name with precalculated base hashNguyễn Thái Ngọc Duy, Mar 12, 2013
  47. 13/13 read_directory: calculate name hashes incrementallyNguyễn Thái Ngọc Duy, Mar 12, 2013
  48. Duy NguyenMar 14, 2013

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