Bug#20752: BENCHMARK with many iterations returns too quickly

In BENCHMARK(count, expr), count could overflow/wrap-around.
Patch changes to a sufficiently large data-type. Adds a warning
for negative count values.


mysql-test/r/func_str.result:
  show that a negative 'count' for BENCHMARK(count, expr)
  throws a warning and returns NULL.
mysql-test/t/func_str.test:
  show that a negative 'count' for BENCHMARK(count, expr)
  throws a warning and returns NULL.
sql/item_func.cc:
  use ulonglong rather than ulong in BENCHMARK(count, expr)
  throw warning on negative 'count'; return SQL-NULL.

1 files changed, 5 insertions, 0 deletions

diff --git a/mysql-test/r/func_str.result b/mysql-test/r/func_str.result
index 6f6edd5112b..8bb764ad608 100644
--- a/mysql-test/r/func_str.result
+++ b/mysql-test/r/func_str.result
@@ -1431,6 +1431,11 @@ benchmark(100, NULL)
 select benchmark(NULL, 1+1);
 benchmark(NULL, 1+1)
 NULL
+select benchmark(-1, 1);
+benchmark(-1, 1)
+NULL
+Warnings:
+Error	1411	Incorrect count value: '-1' for function benchmark
 set @password="password";
 set @my_data="clear text to encode";
 select md5(encode(@my_data, "password"));