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Re: [PATCH v2 02/21] prefix_ref_iterator: break when we leave the prefix

From
Michael Haggerty <mhagger@alum.mit.edu>
Date
Sep 21, 2017, 07:42 UTC
Message-ID
<32b3d338-6781-a600-2c7e-65dc2818aab5@alum.mit.edu>
In-Reply-To
<CAGZ79kbwCAidGR3cgukdjckZVYwj+qbOikqN-e934uP1yk9Cuw@mail.gmail.com>
On 09/20/2017 10:25 PM, Stefan Beller wrote:
Show 13 quoted lines
> On Mon, Sep 18, 2017 at 11:22 PM, Michael Haggerty <mhagger@alum.mit.edu> wrote:
>> [...]
>> +/* Return -1, 0, 1 if refname is before, inside, or after the prefix. */
>> +static int compare_prefix(const char *refname, const char *prefix)
>> +{
>> +       while (*prefix) {
>> +               if (*refname != *prefix)
>> +                       return ((unsigned char)*refname < (unsigned char)*prefix) ? -1 : +1;
> 
> This looks interesting.
> 
> We get a signed char* , cast it to unsigned char* and then
> compare byte by byte.

Not quite. We get a `char *` of unknown signedness (it's implementation-dependent), dereference it into a `char`, then cast that value to `unsigned char`. What you described would be

    *(const unsigned char *)refname < *(const unsigned char *)prefix

But I assume that these two variants would result in identical assembly code.

> [...]
Michael
Previous: Stefan BellerNext: Michael Haggerty
Message 6 of 40 in “Read `packed-refs` using mmap()”
  1. 00/21 Read `packed-refs` using mmap()Michael Haggerty, Sep 19, 2017
  2. 02/21 prefix_ref_iterator: break when we leave the prefixMichael Haggerty, Sep 19, 2017
  3. Stefan BellerSep 20, 2017
  4. Jeff KingSep 21, 2017
  5. Stefan BellerSep 21, 2017
  6. Michael HaggertySep 21, 2017
  7. 04/21 die_unterminated_line(), die_invalid_line(): new functionsMichael Haggerty, Sep 19, 2017
  8. 05/21 read_packed_refs(): use mmap to read the `packed-refs` fileMichael Haggerty, Sep 19, 2017
  9. 08/21 read_packed_refs(): read references with minimal copyingMichael Haggerty, Sep 19, 2017
  10. Jeff KingSep 20, 2017
  11. Michael HaggertySep 21, 2017
  12. 09/21 packed_ref_cache: remember the file-wide peeling stateMichael Haggerty, Sep 19, 2017
  13. 10/21 mmapped_ref_iterator: add iterator over a packed-refs fileMichael Haggerty, Sep 19, 2017
  14. 11/21 mmapped_ref_iterator_advance(): no peeled value for broken refsMichael Haggerty, Sep 19, 2017
  15. Jeff KingSep 20, 2017
  16. 12/21 packed-backend.c: reorder some definitionsMichael Haggerty, Sep 19, 2017
  17. 13/21 packed_ref_cache: keep the `packed-refs` file mmapped if possibleMichael Haggerty, Sep 19, 2017
  18. Michael HaggertySep 19, 2017
  19. Junio C HamanoSep 24, 2017
  20. Jeff KingSep 20, 2017
  21. Jeff KingSep 20, 2017
  22. Michael HaggertySep 21, 2017
  23. 14/21 read_packed_refs(): ensure that references are ordered when readMichael Haggerty, Sep 19, 2017
  24. Jeff KingSep 20, 2017
  25. Michael HaggertySep 21, 2017
  26. Johannes SchindelinSep 25, 2017
  27. 15/21 packed_ref_iterator_begin(): iterate using `mmapped_ref_iterator`Michael Haggerty, Sep 19, 2017
  28. 18/21 packed_ref_store: get rid of the `ref_cache` entirelyMichael Haggerty, Sep 19, 2017
  29. 19/21 ref_cache: remove support for storing peeled valuesMichael Haggerty, Sep 19, 2017
  30. 16/21 packed_read_raw_ref(): read the reference from the mmapped bufferMichael Haggerty, Sep 19, 2017
  31. 20/21 mmapped_ref_iterator: inline into `packed_ref_iterator`Michael Haggerty, Sep 19, 2017
  32. 21/21 packed-backend.c: rename a bunch of things and update commentsMichael Haggerty, Sep 19, 2017
  33. 17/21 ref_store: implement `refs_peel_ref()` genericallyMichael Haggerty, Sep 19, 2017
  34. 06/21 read_packed_refs(): only check for a header at the top of the fileMichael Haggerty, Sep 19, 2017
  35. 07/21 read_packed_refs(): make parsing of the header line more robustMichael Haggerty, Sep 19, 2017
  36. 01/21 ref_iterator: keep track of whether the iterator output is orderedMichael Haggerty, Sep 19, 2017
  37. 03/21 packed_ref_cache: add a backlink to the associated `packed_ref_store`Michael Haggerty, Sep 19, 2017
  38. Johannes SchindelinSep 19, 2017
  39. Jeff KingSep 20, 2017
  40. Johannes SchindelinSep 25, 2017

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