Bug#49141: Encode function is significantly slower in 5.1 compared to 5.0

The problem was that the multiple evaluations of a ENCODE or
DECODE function within a single statement caused the random
generator to be reinitialized at each evaluation, even though
the parameters were constants.

The solution is to initialize the random generator only once
if the password (seed) parameter is constant.

This patch borrows code and ideas from Georgi Kodinov's patch.

mysql-test/r/func_str.result:
  Add test case result.
mysql-test/r/ps.result:
  Add test case result.
mysql-test/t/func_str.test:
  Add test case for Bug#49141
mysql-test/t/ps.test:
  Add test case for Bug#49141
sql/item_strfunc.cc:
  Move seed generation code to a separate method.
  Seed only once if the password (seed) argument
  is constant.
  Remove duplicated code and use a transform method
  to apply encoding or decoding.
sql/item_strfunc.h:
  Add parameter to signal whether the PRNG is already seeded.
  Introduce transform method.
  Combine val_str methods.
sql/sql_crypt.cc:
  Remove method.
sql/sql_crypt.h:
  Seed is supplied as two long integers.

1 files changed, 4 insertions, 4 deletions

diff --git a/sql/sql_crypt.h b/sql/sql_crypt.h
index a5a6bee8a58..2b56c387bd1 100644
--- a/sql/sql_crypt.h
+++ b/sql/sql_crypt.h
@@ -23,15 +23,15 @@ class SQL_CRYPT :public Sql_alloc
   struct rand_struct rand,org_rand;
   char decode_buff[256],encode_buff[256];
   uint shift;
-  void crypt_init(ulong *seed);
  public:
-  SQL_CRYPT(const char *seed, uint length);
+  SQL_CRYPT() {}
   SQL_CRYPT(ulong *seed)
   {
-    crypt_init(seed);
+    init(seed);
   }
   ~SQL_CRYPT() {}
-  void init() { shift=0; rand=org_rand; }
+  void init(ulong *seed);
+  void reinit() { shift=0; rand=org_rand; }
   void encode(char *str, uint length);
   void decode(char *str, uint length);
 };