[PATCH] name-rev: Fix non-shortest description

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

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Uwe Kleine-König noticed that under certain circumstances, name-rev
picked a non-optimal tag.  Jeff King analyzed that name-rev only
takes into account the number of merge traversals, and then the
_last_ number in the description.

As an easy way to fix it, use a weighting factor for merge traversals:
A merge traversal is now made 65535 times more expensive than a
first-parent traversal.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---

	On Thu, 23 Aug 2007, Uwe Kleine-K?nig wrote:

	> I want to check to which kernel version I need to upgrade to get 
	> a certain feature.  For my case it was introduced in 
	> 0567a0c022d5b.
	> 
	> zeisberg@cassiopeia:~/gsrc/linux-2.6$ 
	> 	rev=0567a0c022d5b343370a343121f38fd89925de55
	> 
	> zeisberg@cassiopeia:~/gsrc/linux-2.6$ git name-rev --tags $rev
	> 0567a0c02[...] tags/v2.6.22~1686^2~1^3~5
	> 
	> zeisberg@cassiopeia:~/gsrc/linux-2.6$ git name-rev --refs=*-rc1 $rev
	> 0567a0c02[...] tags/v2.6.22-rc1~1009^2~1^3~5

	This fixes it.

 builtin-name-rev.c |   21 +++++++++++----------
 1 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/builtin-name-rev.c b/builtin-name-rev.c
index 61eba34..03083e9 100644
--- a/builtin-name-rev.c
+++ b/builtin-name-rev.c
@@ -11,14 +11,17 @@ static const char name_rev_usage[] =
 
 typedef struct rev_name {
 	const char *tip_name;
-	int merge_traversals;
 	int generation;
+	int distance;
 } rev_name;
 
 static long cutoff = LONG_MAX;
 
+/* How many generations are maximally preferred over _one_ merge traversal? */
+#define MERGE_TRAVERSAL_WEIGHT 65535
+
 static void name_rev(struct commit *commit,
-		const char *tip_name, int merge_traversals, int generation,
+		const char *tip_name, int generation, int distance,
 		int deref)
 {
 	struct rev_name *name = (struct rev_name *)commit->util;
@@ -45,13 +48,11 @@ static void name_rev(struct commit *commit,
 		name = xmalloc(sizeof(rev_name));
 		commit->util = name;
 		goto copy_data;
-	} else if (name->merge_traversals > merge_traversals ||
-			(name->merge_traversals == merge_traversals &&
-			 name->generation > generation)) {
+	} else if (name->distance > distance) {
 copy_data:
 		name->tip_name = tip_name;
-		name->merge_traversals = merge_traversals;
 		name->generation = generation;
+		name->distance = distance;
 	} else
 		return;
 
@@ -74,11 +75,11 @@ copy_data:
 				sprintf(new_name, "%.*s^%d", len, tip_name,
 						parent_number);
 
-			name_rev(parents->item, new_name,
-				merge_traversals + 1 , 0, 0);
+			name_rev(parents->item, new_name, 0,
+				distance + MERGE_TRAVERSAL_WEIGHT, 0);
 		} else {
-			name_rev(parents->item, tip_name, merge_traversals,
-				generation + 1, 0);
+			name_rev(parents->item, tip_name, generation + 1,
+				distance + 1, 0);
 		}
 	}
 }
-- 
1.5.3.rc6.52.g5113-dirty