GHash, EdgeHash: add debugging function to measure the hash quality

Can use to check on improvements to hash functions.

4 files changed, 80 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_edgehash.h b/source/blender/blenlib/BLI_edgehash.h
index c0529d9032d..a5ec69cae3a 100644
--- a/source/blender/blenlib/BLI_edgehash.h
+++ b/source/blender/blenlib/BLI_edgehash.h
@@ -114,5 +114,9 @@ BLI_INLINE void BLI_edgesetIterator_getKey(EdgeSetIterator *esi, unsigned int *r
 BLI_INLINE void BLI_edgesetIterator_step(EdgeSetIterator *esi) { BLI_edgehashIterator_step((EdgeHashIterator *)esi); }
 BLI_INLINE bool BLI_edgesetIterator_isDone(EdgeSetIterator *esi) { return BLI_edgehashIterator_isDone((EdgeHashIterator *)esi); }
 
+#ifdef DEBUG
+double          BLI_edgehash_calc_quality(EdgeHash *eh);
+double          BLI_edgeset_calc_quality(EdgeSet *es);
+#endif
 
 #endif  /* __BLI_EDGEHASH_H__ */
diff --git a/source/blender/blenlib/BLI_ghash.h b/source/blender/blenlib/BLI_ghash.h
index a59023d4f9b..dc29a129dbf 100644
--- a/source/blender/blenlib/BLI_ghash.h
+++ b/source/blender/blenlib/BLI_ghash.h
@@ -224,6 +224,11 @@ BLI_INLINE bool BLI_gsetIterator_done(GSetIterator *gsi) { return BLI_ghashItera
 	     BLI_gsetIterator_done(&gs_iter_) == false;                           \
 	     BLI_gsetIterator_step(&gs_iter_), i_++)
 
+#ifdef DEBUG
+double BLI_ghash_calc_quality(GHash *gh);
+double BLI_gset_calc_quality(GSet *gs);
+#endif
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/source/blender/blenlib/intern/BLI_ghash.c b/source/blender/blenlib/intern/BLI_ghash.c
index b30553d0b5e..d24c180dae6 100644
--- a/source/blender/blenlib/intern/BLI_ghash.c
+++ b/source/blender/blenlib/intern/BLI_ghash.c
@@ -996,3 +996,39 @@ GSet *BLI_gset_pair_new(const char *info)
 }
 
 /** \} */
+
+
+/** \name Debugging & Introspection
+ * \{ */
+#ifdef DEBUG
+
+/**
+ * Measure how well the hash function performs
+ * (1.0 is approx as good as random distribution).
+ */
+double BLI_ghash_calc_quality(GHash *gh)
+{
+	uint64_t sum = 0;
+	unsigned int i;
+
+	if (gh->nentries == 0)
+		return -1.0;
+
+	for (i = 0; i < gh->nbuckets; i++) {
+		uint64_t count = 0;
+		Entry *e;
+		for (e = gh->buckets[i]; e; e = e->next) {
+			count += 1;
+		}
+		sum += count * (count + 1);
+	}
+	return ((double)sum * (double)gh->nbuckets /
+	        ((double)gh->nentries * (gh->nentries + 2 * gh->nbuckets - 1)));
+}
+double BLI_gset_calc_quality(GSet *gs)
+{
+	return BLI_ghash_calc_quality((GHash *)gs);
+}
+
+#endif
+/** \} */
diff --git a/source/blender/blenlib/intern/edgehash.c b/source/blender/blenlib/intern/edgehash.c
index aa571bbc1c5..b4b3f0dbda3 100644
--- a/source/blender/blenlib/intern/edgehash.c
+++ b/source/blender/blenlib/intern/edgehash.c
@@ -623,3 +623,38 @@ void BLI_edgeset_free(EdgeSet *es)
 }
 
 /** \} */
+
+/** \name Debugging & Introspection
+ * \{ */
+#ifdef DEBUG
+
+/**
+ * Measure how well the hash function performs
+ * (1.0 is approx as good as random distribution).
+ */
+double BLI_edgehash_calc_quality(EdgeHash *eh)
+{
+	uint64_t sum = 0;
+	unsigned int i;
+
+	if (eh->nentries == 0)
+		return -1.0;
+
+	for (i = 0; i < eh->nbuckets; i++) {
+		uint64_t count = 0;
+		EdgeEntry *e;
+		for (e = eh->buckets[i]; e; e = e->next) {
+			count += 1;
+		}
+		sum += count * (count + 1);
+	}
+	return ((double)sum * (double)eh->nbuckets /
+	        ((double)eh->nentries * (eh->nentries + 2 * eh->nbuckets - 1)));
+}
+double BLI_edgeset_calc_quality(EdgeSet *es)
+{
+	return BLI_edgehash_calc_quality((EdgeHash *)es);
+}
+
+#endif
+/** \} */