htable: use precalculated list of primes (#3739)

extra-cmds/utiltest.c

@@ -215,6 +215,24 @@ static void test_htable_update(void)
 	hashTableDelete(htable);
 }
 
+static void test_htable_grow(void)
+{
+	hashTable *htable;
+	int i;
+	char keyBuf[20];
+
+	htable = hashTableNew (3, hashCstrhash, hashCstreq, eFree, NULL);
+
+	for (i = 0; i < 1000; ++i)
+	{
+		snprintf(keyBuf, sizeof(keyBuf), "str_%d", i);
+		hashTablePutItem (htable, strdup(keyBuf), strdup(keyBuf));
+	}
+
+	TEST_CHECK (strcmp (hashTableGetItem (htable, "str_123"), "str_123") == 0);
+	hashTableDelete(htable);
+}
+
 static void test_routines_strrstr(void)
 {
 	TEST_CHECK(strcmp(strrstr("abcdcdb", "cd"), "cdb") == 0);
@@ -225,6 +243,7 @@ TEST_LIST = {
    { "fname/absolute+cache", test_fname_absolute_with_cache },
    { "fname/relative",   test_fname_relative   },
    { "htable/update",    test_htable_update    },
+   { "htable/grow",      test_htable_grow      },
    { "routines/strrstr", test_routines_strrstr },
    { NULL, NULL }     /* zeroed record marking the end of the list */
 };

main/htable.c

@@ -258,24 +258,25 @@ static void       hashTablePutItem00    (hashTable *htable, void *key, void *val
 	htable->count++;
 }
 
-/* TODO: A pre-calculated array can be used instead of
- * finding a new one at runtume. */
+/* "doubling" primes smaller than 2^32 */
+static const unsigned int primes[] = {
+	3, 7, 17, 37, 79, 163, 331, 673, 1361, 2729, 5471, 10949, 21911,
+	43853, 87719, 175447, 350899, 701819, 1403641, 2807303, 5614657,
+	11229331, 22458671, 44917381, 89834777, 179669557, 359339171,
+	718678369, 1437356741, 2874713497,
+};
+
 static unsigned int
 prime_double(unsigned int i)
 {
+	unsigned int j;
+
 	Assert (i > 2);
 	Assert (i % 2);
 
-	for (unsigned int c = 2 * i + 1; ; c += 2)
-	{
-		for (unsigned int i0 = 3; i0 < i; i0 += 2)
-		{
-			if ((c % i0) == 0)
-				goto next;
-		}
-		return c;
-	next:;
-	}
+	for (j = 0; j < sizeof(primes) / sizeof(primes[0]); ++j)
+		if (primes[j] > i)
+			return primes[j];
 
 	return i;
 }