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.

4 files changed, 51 insertions, 50 deletions

diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index 183a628f8e4..b6d3f45f4c2 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -1720,68 +1720,65 @@ String *Item_func_encrypt::val_str(String *str)
 #endif	/* HAVE_CRYPT */
 }
 
+bool Item_func_encode::seed()
+{
+  char buf[80];
+  ulong rand_nr[2];
+  String *key, tmp(buf, sizeof(buf), system_charset_info);
+
+  if (!(key= args[1]->val_str(&tmp)))
+    return TRUE;
+
+  hash_password(rand_nr, key->ptr(), key->length());
+  sql_crypt.init(rand_nr);
+
+  return FALSE;
+}
+
 void Item_func_encode::fix_length_and_dec()
 {
   max_length=args[0]->max_length;
   maybe_null=args[0]->maybe_null || args[1]->maybe_null;
   collation.set(&my_charset_bin);
+  /* Precompute the seed state if the item is constant. */
+  seeded= args[1]->const_item() &&
+          (args[1]->result_type() == STRING_RESULT) && !seed();
 }
 
 String *Item_func_encode::val_str(String *str)
 {
   String *res;
-  char pw_buff[80];
-  String tmp_pw_value(pw_buff, sizeof(pw_buff), system_charset_info);
-  String *password;
   DBUG_ASSERT(fixed == 1);
 
   if (!(res=args[0]->val_str(str)))
   {
-    null_value=1; /* purecov: inspected */
-    return 0; /* purecov: inspected */
+    null_value= 1;
+    return NULL;
   }
 
-  if (!(password=args[1]->val_str(& tmp_pw_value)))
+  if (!seeded && seed())
   {
-    null_value=1;
-    return 0;
+    null_value= 1;
+    return NULL;
   }
 
-  null_value=0;
-  res=copy_if_not_alloced(str,res,res->length());
-  SQL_CRYPT sql_crypt(password->ptr(), password->length());
-  sql_crypt.init();
-  sql_crypt.encode((char*) res->ptr(),res->length());
-  res->set_charset(&my_charset_bin);
+  null_value= 0;
+  res= copy_if_not_alloced(str, res, res->length());
+  transform(res);
+  sql_crypt.reinit();
+
   return res;
 }
 
-String *Item_func_decode::val_str(String *str)
+void Item_func_encode::transform(String *res)
 {
-  String *res;
-  char pw_buff[80];
-  String tmp_pw_value(pw_buff, sizeof(pw_buff), system_charset_info);
-  String *password;
-  DBUG_ASSERT(fixed == 1);
-
-  if (!(res=args[0]->val_str(str)))
-  {
-    null_value=1; /* purecov: inspected */
-    return 0; /* purecov: inspected */
-  }
-
-  if (!(password=args[1]->val_str(& tmp_pw_value)))
-  {
-    null_value=1;
-    return 0;
-  }
+  sql_crypt.encode((char*) res->ptr(),res->length());
+  res->set_charset(&my_charset_bin);
+}
 
-  null_value=0;
-  res=copy_if_not_alloced(str,res,res->length());
-  SQL_CRYPT sql_crypt(password->ptr(), password->length());
-  sql_crypt.init();
+void Item_func_decode::transform(String *res)
+{
   sql_crypt.decode((char*) res->ptr(),res->length());
-  return res;
 }
 
 
diff --git a/sql/item_strfunc.h b/sql/item_strfunc.h
index 2cdb45100ae..59241872e63 100644
--- a/sql/item_strfunc.h
+++ b/sql/item_strfunc.h
@@ -351,12 +351,22 @@ public:
 
 class Item_func_encode :public Item_str_func
 {
+private:
+  /** Whether the PRNG has already been seeded. */
+  bool seeded;
+protected:
+  SQL_CRYPT sql_crypt;
 public:
   Item_func_encode(Item *a, Item *seed):
     Item_str_func(a, seed) {}
   String *val_str(String *);
   void fix_length_and_dec();
   const char *func_name() const { return "encode"; }
+protected:
+  virtual void transform(String *);
+private:
+  /** Provide a seed for the PRNG sequence. */
+  bool seed();
 };
 
 
@@ -364,8 +374,9 @@ class Item_func_decode :public Item_func_encode
 {
 public:
   Item_func_decode(Item *a, Item *seed): Item_func_encode(a, seed) {}
-  String *val_str(String *);
   const char *func_name() const { return "decode"; }
+protected:
+  void transform(String *);
 };
 
 
diff --git a/sql/sql_crypt.cc b/sql/sql_crypt.cc
index c4f93cc2a33..3d7d248782b 100644
--- a/sql/sql_crypt.cc
+++ b/sql/sql_crypt.cc
@@ -28,14 +28,7 @@
 
 #include "mysql_priv.h"
 
-SQL_CRYPT::SQL_CRYPT(const char *password, uint length)
-{
-  ulong rand_nr[2];
-  hash_password(rand_nr,password, length);
-  crypt_init(rand_nr);
-}
-
-void SQL_CRYPT::crypt_init(ulong *rand_nr)
+void SQL_CRYPT::init(ulong *rand_nr)
 {
   uint i;
   randominit(&rand,rand_nr[0],rand_nr[1]);
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);
 };