git/list[1] front-page[2] threads[3] people[4] search[5] about
 

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

From
Duy Nguyen <pclouds@gmail.com>
Date
Mar 10, 2013, 12:06 UTC
Message-ID
<CACsJy8A4+2t=PMJ+iSFFz-fafkAHYGvm6G4M-qpiO9674sanEQ@mail.gmail.com>
In-Reply-To
<CALWbr2x6V6TB9g_nQCgG2r9L__a2wxG28Qi5KTXChHxj5JSQ8w@mail.gmail.com>
On Sun, Mar 10, 2013 at 6:54 PM, Antoine Pelisse <apelisse@gmail.com> wrote:
Show 15 quoted lines
> On Sun, Mar 10, 2013 at 12:43 PM, Antoine Pelisse <apelisse@gmail.com> wrote:
>> On Sun, Mar 10, 2013 at 11:38 AM, Duy Nguyen <pclouds@gmail.com> wrote:
>>> glibc's C strncmp version does 4-byte comparison at a time when n >=4,
>>> then fall back to 1-byte for the rest.
>>
>> Looking at this
>> (http://fossies.org/dox/glibc-2.17/strncmp_8c_source.html), it's not
>> exactly true.
>>
>> It would rather be while (n >= 4), manually unroll the loop.
>
> By the way, if we know the length of the string, we could use memcmp.
> This one is allowed to compare 4-bytes at a time (he doesn't care
> about end of string). This is true because the value of the length
> parameter is no longer "at most".

We still need to worry about access violation after NUL when two strings have different lengths. That could be avoided in this particular case, but I think it's too fragile.

-- 
Duy
Previous: Antoine PelisseNext: Antoine Pelisse
Message 17 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

Read the whole thread, see it on lore, or plain text.

$ cat FOOTERMessages come from the public archive at lore.kernel.org/git, fetched every hour. The front page is chosen and written each morning by an AI editor and can be wrong; the threads themselves are the record. About and API. For agents: an MCP server at https://gitlist.dev/mcp, and any thread, story or person page as Markdown by adding .md to its URL (or sending Accept: text/markdown). Details in /llms.txt.