htable: reduce size of htable by storing perfect bitnum, not mask.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

ccan/htable/htable.c

@@ -58,6 +58,15 @@ static inline bool entry_is_valid(uintptr_t e)
 	return e > HTABLE_DELETED;
 }
 
+/* We use 0 to mean we don't have a perfect bit, otherwise it's
+ * bit n - 1 */
+static inline uintptr_t ht_perfect_mask(const struct htable *ht)
+{
+	if (ht->perfect_bitnum > 0)
+		return (uintptr_t)1 << (ht->perfect_bitnum - 1);
+	return 0;
+}
+
 static inline uintptr_t get_hash_ptr_bits(const struct htable *ht,
 					  size_t hash)
 {
@@ -65,7 +74,7 @@ static inline uintptr_t get_hash_ptr_bits(const struct htable *ht,
 	 * end is quite expensive.  But the lower bits are redundant, so
 	 * we fold the value first. */
 	return (hash ^ (hash >> ht->bits))
-		& ht->common_mask & ~ht->perfect_bit;
+		& ht->common_mask & ~ht_perfect_mask(ht);
 }
 
 void htable_init(struct htable *ht,
@@ -75,7 +84,7 @@ void htable_init(struct htable *ht,
 	*ht = empty;
 	ht->rehash = rehash;
 	ht->priv = priv;
-	ht->table = &ht->perfect_bit;
+	ht->table = &ht->common_bits;
 }
 
 static inline size_t ht_max(const struct htable *ht)
@@ -102,7 +111,7 @@ bool htable_init_sized(struct htable *ht,
 
 	ht->table = htable_alloc(ht, sizeof(size_t) << ht->bits);
 	if (!ht->table) {
-		ht->table = &ht->perfect_bit;
+		ht->table = &ht->common_bits;
 		return false;
 	}
 	(void)htable_debug(ht, HTABLE_LOC);
@@ -111,7 +120,7 @@ bool htable_init_sized(struct htable *ht,
 	
 void htable_clear(struct htable *ht)
 {
-	if (ht->table != &ht->perfect_bit)
+	if (ht->table != &ht->common_bits)
 		htable_free(ht, (void *)ht->table);
 	htable_init(ht, ht->rehash, ht->priv);
 }
@@ -154,7 +163,7 @@ void *htable_firstval_(const struct htable *ht,
 		       struct htable_iter *i, size_t hash)
 {
 	i->off = hash_bucket(ht, hash);
-	return htable_val(ht, i, hash, ht->perfect_bit);
+	return htable_val(ht, i, hash, ht_perfect_mask(ht));
 }
 
 void *htable_nextval_(const struct htable *ht,
@@ -197,7 +206,7 @@ void *htable_prev_(const struct htable *ht, struct htable_iter *i)
 static void ht_add(struct htable *ht, const void *new, size_t h)
 {
 	size_t i;
-	uintptr_t perfect = ht->perfect_bit;
+	uintptr_t perfect = ht_perfect_mask(ht);
 
 	i = hash_bucket(ht, h);
 
@@ -223,16 +232,16 @@ static COLD bool double_table(struct htable *ht)
 	ht->bits++;
 
 	/* If we lost our "perfect bit", get it back now. */
-	if (!ht->perfect_bit && ht->common_mask) {
+	if (ht->perfect_bitnum == 0 && ht->common_mask) {
 		for (i = 0; i < sizeof(ht->common_mask) * CHAR_BIT; i++) {
 			if (ht->common_mask & ((size_t)1 << i)) {
-				ht->perfect_bit = (size_t)1 << i;
+				ht->perfect_bitnum = i + 1;
 				break;
 			}
 		}
 	}
 
-	if (oldtable != &ht->perfect_bit) {
+	if (oldtable != &ht->common_bits) {
 		for (i = 0; i < oldnum; i++) {
 			if (entry_is_valid(e = oldtable[i])) {
 				void *p = get_raw_ptr(ht, e);
@@ -262,7 +271,7 @@ static COLD void rehash_table(struct htable *ht)
 			continue;
 		if (e == HTABLE_DELETED)
 			ht->table[h] = 0;
-		else if (!(e & ht->perfect_bit)) {
+		else if (!(e & ht_perfect_mask(ht))) {
 			void *p = get_raw_ptr(ht, e);
 			ht->table[h] = 0;
 			ht_add(ht, p, ht->rehash(p, ht->priv));
@@ -290,7 +299,7 @@ static COLD void update_common(struct htable *ht, const void *p)
 
 		ht->common_mask = ~((uintptr_t)1 << i);
 		ht->common_bits = ((uintptr_t)p & ht->common_mask);
-		ht->perfect_bit = 1;
+		ht->perfect_bitnum = 1;
 		(void)htable_debug(ht, HTABLE_LOC);
 		return;
 	}
@@ -313,7 +322,8 @@ static COLD void update_common(struct htable *ht, const void *p)
 	/* Take away those bits from our mask, bits and perfect bit. */
 	ht->common_mask &= ~maskdiff;
 	ht->common_bits &= ~maskdiff;
-	ht->perfect_bit &= ~maskdiff;
+	if (ht_perfect_mask(ht) & maskdiff)
+		ht->perfect_bitnum = 0;
 	(void)htable_debug(ht, HTABLE_LOC);
 }
 

ccan/htable/htable.h

@@ -24,11 +24,10 @@
 struct htable {
 	size_t (*rehash)(const void *elem, void *priv);
 	void *priv;
-	unsigned int bits;
+	unsigned int bits, perfect_bitnum;
 	size_t elems, deleted;
 	/* These are the bits which are the same in all pointers. */
 	uintptr_t common_mask, common_bits;
-	uintptr_t perfect_bit;
 	uintptr_t *table;
 };
 
@@ -50,7 +49,7 @@ struct htable {
  *	static struct htable ht = HTABLE_INITIALIZER(ht, rehash, NULL);
  */
 #define HTABLE_INITIALIZER(name, rehash, priv)				\
-	{ rehash, priv, 0, 0, 0, -1, 0, 0, &name.perfect_bit }
+	{ rehash, priv, 0, 0, 0, 0, -1, 0, &name.common_bits }
 
 /**
  * htable_init - initialize an empty hash table.

ccan/htable/test/run-debug.c

@@ -194,17 +194,17 @@ int main(void)
 	/* Corner cases: wipe out the perfect bit using bogus pointer. */
 	htable_clear(&ht);
 	htable_add(&ht, hash(&val[NUM_VALS-1], NULL), &val[NUM_VALS-1]);
-	ok1(ht.perfect_bit);
-	perfect_bit = ht.perfect_bit;
+	ok1(ht_perfect_mask(&ht));
+	perfect_bit = ht_perfect_mask(&ht);
 	bad_pointer = (void *)((uintptr_t)&val[NUM_VALS-1] | perfect_bit);
 	htable_add(&ht, 0, bad_pointer);
-	ok1(ht.perfect_bit == 0);
+	ok1(ht_perfect_mask(&ht) == 0);
 	htable_del(&ht, 0, bad_pointer);
 
 	/* Enlarging should restore it... */
 	add_vals(&ht, val, 0, NUM_VALS-1);
 
-	ok1(ht.perfect_bit != 0);
+	ok1(ht_perfect_mask(&ht) != 0);
 	htable_clear(&ht);
 
 	ok1(htable_init_sized(&ht, hash, NULL, 1024));

ccan/htable/test/run.c

@@ -183,17 +183,17 @@ int main(void)
 	/* Corner cases: wipe out the perfect bit using bogus pointer. */
 	htable_clear(&ht);
 	htable_add(&ht, 0, (void *)((uintptr_t)&val[NUM_VALS-1]));
-	ok1(ht.perfect_bit);
-	perfect_bit = ht.perfect_bit;
+	ok1(ht_perfect_mask(&ht));
+	perfect_bit = ht_perfect_mask(&ht);
 	htable_add(&ht, 0, (void *)((uintptr_t)&val[NUM_VALS-1]
 				   | perfect_bit));
-	ok1(ht.perfect_bit == 0);
+	ok1(ht_perfect_mask(&ht) == 0);
 	htable_del(&ht, 0, (void *)((uintptr_t)&val[NUM_VALS-1] | perfect_bit));
 
 	/* Enlarging should restore it... */
 	add_vals(&ht, val, 0, NUM_VALS-1);
 
-	ok1(ht.perfect_bit != 0);
+	ok1(ht_perfect_mask(&ht) != 0);
 	htable_clear(&ht);
 
 	ok1(htable_init_sized(&ht, hash, NULL, 1024));

ccan/htable/tools/speed.c

@@ -74,8 +74,8 @@ static size_t perfect(const struct htable *ht)
 			continue;
 		if (hash_bucket(ht, ht->rehash(get_raw_ptr(ht, ht->table[i]),
 					       ht->priv)) == i) {
-			assert((ht->table[i] & ht->perfect_bit)
-			       == ht->perfect_bit);
+			assert((ht->table[i] & ht_perfect_mask(ht))
+			       == ht_perfect_mask(ht));
 			placed_perfect++;
 		}
 	}