Re: [PATCH v2] commit.c: use the generic "sha1_pos" function for lookup
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Feb 27, 2014, 19:06 UTC
- Message-ID
- <xmqqppm8z86l.fsf@gitster.dls.corp.google.com>
- In-Reply-To
- <530E3732.3060708@yandex.ru>
"Dmitry S. Dolzhenko" <dmitrys.dolzhenko@yandex.ru> writes:
Show 5 quoted lines
> Refactor binary search in "commit_graft_pos" function: use > generic "sha1_pos" function. > > Signed-off-by: Dmitry S. Dolzhenko <dmitrys.dolzhenko@yandex.ru> > ---
Looks trivially correct; thanks.
Looking at this patch makes me wonder why we have sha1_pos() and sha1_entry_pos() helper functions, though. It feels as if the former could be written in terms of the latter, but there may be some performance and correctness downsides if we did so:
- rewriting sha1_entry_pos() in terms of sha1_pos() would add the cost of callback to obtain the keys;
- sha1_entry_pos() picks the middle location conservatively to avoid overshooting penalty, which sha1_pos() does not do;
- sha1_entry_pos() has been updated recently to tolerate duplicates.
Show 47 quoted lines
> commit.c | 24 +++++++++---------------
> 1 file changed, 9 insertions(+), 15 deletions(-)
>
> diff --git a/commit.c b/commit.c
> index 6bf4fe0..6ceee6a 100644
> --- a/commit.c
> +++ b/commit.c
> @@ -10,6 +10,7 @@
> #include "mergesort.h"
> #include "commit-slab.h"
> #include "prio-queue.h"
> +#include "sha1-lookup.h"
>
> static struct commit_extra_header *read_commit_extra_header_lines(const char *buf, size_t len, const char **);
>
> @@ -114,23 +115,16 @@ static unsigned long parse_commit_date(const char *buf, const char *tail)
> static struct commit_graft **commit_graft;
> static int commit_graft_alloc, commit_graft_nr;
>
> +static const unsigned char *commit_graft_sha1_access(size_t index, void *table)
> +{
> + struct commit_graft **commit_graft_table = table;
> + return commit_graft_table[index]->sha1;
> +}
> +
> static int commit_graft_pos(const unsigned char *sha1)
> {
> - int lo, hi;
> - lo = 0;
> - hi = commit_graft_nr;
> - while (lo < hi) {
> - int mi = (lo + hi) / 2;
> - struct commit_graft *graft = commit_graft[mi];
> - int cmp = hashcmp(sha1, graft->sha1);
> - if (!cmp)
> - return mi;
> - if (cmp < 0)
> - hi = mi;
> - else
> - lo = mi + 1;
> - }
> - return -lo - 1;
> + return sha1_pos(sha1, commit_graft, commit_graft_nr,
> + commit_graft_sha1_access);
> }
>
> int register_commit_graft(struct commit_graft *graft, int ignore_dups)