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Re: [PATCH 3/6] find_reference_location(): make function safe for empty snapshots

From
Jeff King <peff@peff.net>
Date
Jan 24, 2018, 20:27 UTC
Message-ID
<20180124202754.GA7773@sigill.intra.peff.net>
In-Reply-To
<e9f9ed1944c297a68c2b76f5d4ddd73e279bd207.1516791909.git.mhagger@alum.mit.edu>
On Wed, Jan 24, 2018 at 12:14:13PM +0100, Michael Haggerty wrote:
Show 13 quoted lines
> diff --git a/refs/packed-backend.c b/refs/packed-backend.c
> index 08698de6ea..361affd7ad 100644
> --- a/refs/packed-backend.c
> +++ b/refs/packed-backend.c
> [...]
> @@ -551,7 +553,7 @@ static const char *find_reference_location(struct snapshot *snapshot,
>  	 */
>  	const char *hi = snapshot->eof;
>  
> -	while (lo < hi) {
> +	while (lo != hi) {
>  		const char *mid, *rec;
>  		int cmp;

This tightens the binary search termination condition. If we ever did see "hi > lo", we'd want to terminate the loop. Is that ever possible?

I think the answer is "no". Our "hi" here is an exclusive bound, so we should never go past it via find_end_of_record() when assigning "lo". And "hi" is always assigned from the start of the current record. That can never cross "lo", because find_start_of_record() ensures it.

So I think it's fine, but I wanted to double check.
-Peff
Previous: Michael HaggertyNext: Junio C Hamano
Message 25 of 33 in “packed_ref_cache: don't use mmap() for small files”
  1. packed_ref_cache: don't use mmap() for small filesKim Gybels, Jan 13, 2018
  2. Johannes SchindelinJan 13, 2018
  3. packed_ref_cache: don't use mmap() for small filesKim Gybels, Jan 14, 2018
  4. 0/3 Supplements to "packed_ref_cache: don't use mmap() for small files"Michael Haggerty, Jan 15, 2018
  5. Johannes SchindelinJan 17, 2018
  6. Junio C HamanoJan 17, 2018
  7. 1/3 SQUASH? Mention that `snapshot::buf` can be NULL for empty filesMichael Haggerty, Jan 15, 2018
  8. 2/3 create_snapshot(): exit early if the file was emptyMichael Haggerty, Jan 15, 2018
  9. 3/3 find_reference_location(): don't invoke if `snapshot->buf` is NULLMichael Haggerty, Jan 15, 2018
  10. Jeff KingJan 15, 2018
  11. Kim GybelsJan 15, 2018
  12. Jeff KingJan 15, 2018
  13. packed_ref_cache: don't use mmap() for small filesKim Gybels, Jan 16, 2018
  14. Jeff KingJan 17, 2018
  15. Michael HaggertyJan 21, 2018
  16. Junio C HamanoJan 22, 2018
  17. Michael HaggertyJan 24, 2018
  18. 0/6 Yet another approach to handling empty snapshotsMichael Haggerty, Jan 24, 2018
  19. Jeff KingJan 24, 2018
  20. Junio C HamanoJan 24, 2018
  21. Johannes SchindelinFeb 15, 2018
  22. 1/6 struct snapshot: store `start` rather than `header_len`Michael Haggerty, Jan 24, 2018
  23. Jeff KingJan 24, 2018
  24. 3/6 find_reference_location(): make function safe for empty snapshotsMichael Haggerty, Jan 24, 2018
  25. Jeff KingJan 24, 2018
  26. Junio C HamanoJan 24, 2018
  27. Jeff KingJan 24, 2018
  28. 2/6 create_snapshot(): use `xmemdupz()` rather than a strbufMichael Haggerty, Jan 24, 2018
  29. 5/6 load_contents(): don't try to mmap an empty fileMichael Haggerty, Jan 24, 2018
  30. 4/6 packed_ref_iterator_begin(): make optimization more generalMichael Haggerty, Jan 24, 2018
  31. Jeff KingJan 24, 2018
  32. 6/6 packed_ref_cache: don't use mmap() for small filesMichael Haggerty, Jan 24, 2018
  33. Junio C HamanoJan 24, 2018

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