htable: htable_pick helper to select a random entry.

[ccan] / ccan / htable / htable.c

diff --git a/ccan/htable/htable.c b/ccan/htable/htable.c
index 2028d336aec20bff59201c13074602dadd144ec7..cffd0619d338d8146365abd3f10e1b308ef4c4d4 100644 (file)
--- a/ccan/htable/htable.c
+++ b/ccan/htable/htable.c
@@ -11,6 +11,9 @@
 /* We use 0x1 as deleted marker. */
 #define HTABLE_DELETED (0x1)
 
+/* perfect_bitnum 63 means there's no perfect bitnum */
+#define NO_PERFECT_BIT (sizeof(uintptr_t) * CHAR_BIT - 1)
+
 static void *htable_default_alloc(struct htable *ht, size_t len)
 {
        return calloc(len, 1);
@@ -58,6 +61,11 @@ static inline bool entry_is_valid(uintptr_t e)
        return e > HTABLE_DELETED;
 }
 
+static inline uintptr_t ht_perfect_mask(const struct htable *ht)
+{
+       return (uintptr_t)2 << ht->perfect_bitnum;
+}
+
 static inline uintptr_t get_hash_ptr_bits(const struct htable *ht,
                                          size_t hash)
 {
@@ -65,7 +73,7 @@ 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 +83,7 @@ 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 +110,7 @@ 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 +119,7 @@ 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 +162,7 @@ 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 +205,7 @@ 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 +231,16 @@ 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 == NO_PERFECT_BIT && 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;
+                       if (ht->common_mask & ((size_t)2 << i)) {
+                               ht->perfect_bitnum = i;
                                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);
@@ -250,7 +258,7 @@ static COLD bool double_table(struct htable *ht)
 static COLD void rehash_table(struct htable *ht)
 {
        size_t start, i;
-       uintptr_t e;
+       uintptr_t e, perfect = ht_perfect_mask(ht);
 
        /* Beware wrap cases: we need to start from first empty bucket. */
        for (start = 0; ht->table[start]; start++);
@@ -262,7 +270,7 @@ 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 & perfect)) {
                        void *p = get_raw_ptr(ht, e);
                        ht->table[h] = 0;
                        ht_add(ht, p, ht->rehash(p, ht->priv));
@@ -290,7 +298,7 @@ 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 = 0;
                (void)htable_debug(ht, HTABLE_LOC);
                return;
        }
@@ -313,7 +321,8 @@ 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 = NO_PERFECT_BIT;
        (void)htable_debug(ht, HTABLE_LOC);
 }
 
@@ -356,6 +365,20 @@ void htable_delval_(struct htable *ht, struct htable_iter *i)
        ht->deleted++;
 }
 
+void *htable_pick_(const struct htable *ht, size_t seed, struct htable_iter *i)
+{
+       void *e;
+       struct htable_iter unwanted;
+
+       if (!i)
+               i = &unwanted;
+       i->off = seed % ((size_t)1 << ht->bits);
+       e = htable_next(ht, i);
+       if (!e)
+               e = htable_first(ht, i);
+       return e;
+}
+
 struct htable *htable_check(const struct htable *ht, const char *abortstr)
 {
        void *p;