[PATCH] pack-objects: fix delta cache size accounting

[Nicolas Pitre <nico@cam.org>]

The wrong value was substracted from delta_cache_size when replacing
a cached delta, as trg_entry->delta_size was used after the old size
had been replaced by the new size.

Noticed by Linus.

Signed-off-by: Nicolas Pitre <nico@cam.org> 
---

On Fri, 7 Dec 2007, Linus Torvalds wrote:

> The code in try_delta() that replaces a delta cache entry with another one 
> seems very buggy wrt that whole "delta_cache_size" update. It does
> 
> 	delta_cache_size -= trg_entry->delta_size;
> 
> to account for the old delta going away, but it does this *after* having 
> already replaced trg_entry->delta_size with the new delta entry.

Doh!  Mea culpa.

diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index 4f44658..350ece4 100644
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c
@@ -1422,10 +1422,6 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 		}
 	}
 
-	trg_entry->delta = src_entry;
-	trg_entry->delta_size = delta_size;
-	trg->depth = src->depth + 1;
-
 	/*
 	 * Handle memory allocation outside of the cache
 	 * accounting lock.  Compiler will optimize the strangeness
@@ -1439,7 +1435,7 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 		trg_entry->delta_data = NULL;
 	}
 	if (delta_cacheable(src_size, trg_size, delta_size)) {
-		delta_cache_size += trg_entry->delta_size;
+		delta_cache_size += delta_size;
 		cache_unlock();
 		trg_entry->delta_data = xrealloc(delta_buf, delta_size);
 	} else {
@@ -1447,6 +1443,10 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 		free(delta_buf);
 	}
 
+	trg_entry->delta = src_entry;
+	trg_entry->delta_size = delta_size;
+	trg->depth = src->depth + 1;
+
 	return 1;
 }