[PATCH v2] commit.c: use the generic "sha1_pos" function for lookup

Dmitry S. Dolzhenko· Feb 26, 2014, 18:49 UTC · lore

Refactor binary search in "commit_graft_pos" function: use generic "sha1_pos" function.

Signed-off-by: Dmitry S. Dolzhenko <dmitrys.dolzhenko@yandex.ru>
---
 commit.c | 24 +++++++++---------------
 1 file changed, 9 insertions(+), 15 deletions(-)

Show changes to commit.c +9 −15

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)

-- 
1.8.3.2

Junio C Hamano· Feb 27, 2014, 19:06 UTC · re: Dmitry S. Dolzhenko · lore

Re: [PATCH v2] commit.c: use the generic "sha1_pos" function for lookup

"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)

v2commit.c: use the generic "sha1_pos" function for lookup