Optimize the n=1 case of array_rand()

diff --git a/ext/standard/array.c b/ext/standard/array.c
index efe309515c71481d4bc1262965858527fb6e4f7a..3ffced130ceee062710572430336e17bb5bc6d52 100644 (file)
--- a/ext/standard/array.c
+++ b/ext/standard/array.c
@@ -5033,7 +5033,7 @@ PHP_FUNCTION(array_multisort)
 PHP_FUNCTION(array_rand)
 {
        zval *input;
-       zend_long randval, num_req = 1;
+       zend_long num_req = 1;
        zend_string *string_key;
        zend_ulong num_key;
        int i;
@@ -5054,17 +5054,32 @@ PHP_FUNCTION(array_rand)
        }
 
        if (num_req == 1) {
-               randval = php_mt_rand_range(0, num_avail - 1);
+               HashTable *ht = Z_ARRVAL_P(input);
 
-               ZEND_HASH_FOREACH_KEY(Z_ARRVAL_P(input), num_key, string_key) {
-                       if (randval-- == 0) {
-                               if (string_key) {
-                                       RETURN_STR_COPY(string_key);
+               /* Compact the hashtable if less than 3/8 of elements are used */
+               if (num_avail < ht->nNumUsed - (ht->nNumUsed>>1) - (ht->nNumUsed>>2)) {
+                       if (ht->u.flags & HASH_FLAG_PACKED) {
+                               zend_hash_packed_to_hash(ht);
+                       } else {
+                               zend_hash_rehash(ht);
+                       }
+               }
+
+               /* Sample random buckets until we hit one that is not empty.
+                * The worst case probability of hitting an empty element is 1-3/8. The worst case
+                * probability of hitting N empty elements in a row is (1-3/8)**N.
+                * For N=10 this becomes smaller than 1%. */
+               do {
+                       zend_long randval = php_mt_rand_range(0, ht->nNumUsed - 1);
+                       Bucket *bucket = &ht->arData[randval];
+                       if (!Z_ISUNDEF(bucket->val)) {
+                               if (bucket->key) {
+                                       RETURN_STR_COPY(bucket->key);
                                } else {
-                                       RETURN_LONG(num_key);
+                                       RETURN_LONG(bucket->h);
                                }
                        }
-               } ZEND_HASH_FOREACH_END();
+               } while (1);
        }
 
        if (num_req <= 0 || num_req > num_avail) {
@@ -5086,7 +5101,7 @@ PHP_FUNCTION(array_rand)
 
        i = num_req;
        while (i) {
-               randval = php_mt_rand_range(0, num_avail - 1);
+               zend_long randval = php_mt_rand_range(0, num_avail - 1);
                if (!zend_bitset_in(bitset, randval)) {
                        zend_bitset_incl(bitset, randval);
                        i--;