The previous hash bucket culling resulted in a somewhat unpredictable
number of hash bucket entries in the order of magnitude of HASH_LIMIT.
Replace this with a Bresenham-like algorithm leaving us with exactly
HASH_LIMIT entries by uniform culling.
Signed-off-by: David Kastrup <dak@xxxxxxx>
---
This is to be applied on top of the patch for packing the index
structure. Which is the reason it is posted as a followup to the
respective article. In contrast to that patch, this patch has only
been tested/reviewed by myself as to yet.
diff-delta.c | 41 +++++++++++++++++++++++++++++++----------
1 files changed, 31 insertions(+), 10 deletions(-)
diff --git a/diff-delta.c b/diff-delta.c
index d355e5e..1a8d6fb 100644
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -207,19 +207,40 @@ struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
* the reference buffer.
*/
for (i = 0; i < hsize; i++) {
- if (hash_count[i] < HASH_LIMIT)
+ int acc;
+
+ if (hash_count[i] <= HASH_LIMIT)
continue;
+
+ entries -= hash_count[i] - HASH_LIMIT;
+ /* We leave exactly HASH_LIMIT entries in the bucket */
+
entry = hash[i];
+ acc = 0;
do {
- struct unpacked_index_entry *keep = entry;
- int skip = hash_count[i] / HASH_LIMIT;
- do {
- --entries;
- entry = entry->next;
- } while(--skip && entry);
- ++entries;
- keep->next = entry;
- } while(entry);
+ acc += hash_count[i] - HASH_LIMIT;
+ if (acc > 0) {
+ struct unpacked_index_entry *keep = entry;
+ do {
+ entry = entry->next;
+ acc -= HASH_LIMIT;
+ } while (acc > 0);
+ keep->next = entry->next;
+ }
+ entry = entry->next;
+ } while (entry);
+
+ /* Assume that this loop is gone through exactly
+ * HASH_LIMIT times and is entered and left with
+ * acc==0. So the first statement in the loop
+ * contributes (hash_count[i]-HASH_LIMIT)*HASH_LIMIT
+ * to the accumulator, and the inner loop consequently
+ * is run (hash_count[i]-HASH_LIMIT) times, removing
+ * one element from the list each time. Since acc
+ * balances out to 0 at the final run, the inner loop
+ * body can't be left with entry==NULL. So we indeed
+ * encounter entry==NULL in the outer loop only.
+ */
}
free(hash_count);
--
1.5.3.GIT
-
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