Drizzled Public API Documentation

rand_function.cc
1 /* -*- mode: c++; c-basic-offset: 2; indent-tabs-mode: nil; -*-
2  * vim:expandtab:shiftwidth=2:tabstop=2:smarttab:
3  *
4  * Copyright (C) 2008 Sun Microsystems, Inc.
5  * Copyright (C) 2010 Stewart Smith
6  *
7  * This program is free software; you can redistribute it and/or modify
8  * it under the terms of the GNU General Public License as published by
9  * the Free Software Foundation; version 2 of the License.
10  *
11  * This program is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14  * GNU General Public License for more details.
15  *
16  * You should have received a copy of the GNU General Public License
17  * along with this program; if not, write to the Free Software
18  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
19  */
20 
21 #include <config.h>
22 #include <drizzled/plugin/function.h>
23 #include <drizzled/item/func.h>
24 #include <drizzled/function/math/real.h>
25 #include <drizzled/session.h>
26 
27 using namespace std;
28 using namespace drizzled;
29 
31 {
32  uint64_t seed1;
33  uint64_t seed2;
34  uint64_t max_value;
35  double max_value_dbl;
36  void _seed_random_int(uint64_t new_seed1, uint64_t new_seed2);
37 
38 public:
40  double val_real();
41  const char *func_name() const { return "rand"; }
42  bool const_item() const { return 0; }
43  void update_used_tables();
44  bool fix_fields(Session *session, Item **ref);
45 
47  {
48  return (n == 0 || n == 1);
49  }
50 
51 private:
52  void seed_random (Item * val);
53 };
54 
55 static uint32_t sql_rnd()
56 {
57  return (uint32_t) (rand() * 0xffffffff); /* make all bits random */
58 }
59 
60 
61 void RandFunction::seed_random(Item *arg)
62 {
63  /*
64  TODO: do not do reinit 'rand' for every execute of PS/SP if
65  args[0] is a constant.
66  */
67  uint64_t tmp= (uint64_t) arg->val_int();
68  _seed_random_int(tmp * 0x10001L + 55555555L, tmp * 0x10000001L);
69 }
70 
71 void RandFunction::_seed_random_int(uint64_t new_seed1, uint64_t new_seed2)
72 {
73  max_value= 0x3FFFFFFFL;
74  max_value_dbl=(double) max_value;
75  seed1= new_seed1 % max_value;
76  seed2= new_seed2 % max_value;
77 }
78 
79 bool RandFunction::fix_fields(Session *session,Item **ref)
80 {
81  if (Item_real_func::fix_fields(session, ref))
82  return true;
83 
84  used_tables_cache|= RAND_TABLE_BIT;
85  if (arg_count)
86  { // Only use argument once in query
87  /*
88  No need to send a Rand log event if seed was given eg: RAND(seed),
89  as it will be replicated in the query as such.
90  */
91  if (args[0]->const_item())
92  seed_random(args[0]);
93  }
94  else
95  {
96  uint64_t tmp= sql_rnd();
97  _seed_random_int(tmp + (uint64_t) ref, tmp + (uint64_t) session->thread_id);
98  }
99 
100  return false;
101 }
102 
103 void RandFunction::update_used_tables()
104 {
105  Item_real_func::update_used_tables();
106  used_tables_cache|= RAND_TABLE_BIT;
107 }
108 
110 {
111  assert(fixed == 1);
112  if (arg_count && !args[0]->const_item())
113  seed_random(args[0]);
114 
115  seed1= (seed1 * 3 + seed2) % max_value;
116  seed2= (seed1 + seed2 + 33) % max_value;
117  return (((double) seed1) / max_value_dbl);
118 }
119 
120 plugin::Create_function<RandFunction> *rand_function= NULL;
121 
122 static int initialize(module::Context &registry)
123 {
124  rand_function= new plugin::Create_function<RandFunction>("rand");
125  registry.add(rand_function);
126  return 0;
127 }
128 
129 DRIZZLE_DECLARE_PLUGIN
130 {
131  DRIZZLE_VERSION_ID,
132  "rand",
133  "1.0",
134  "Stewart Smith",
135  N_("RAND function"),
136  PLUGIN_LICENSE_GPL,
137  initialize,
138  NULL,
139  NULL,
140 }
141 DRIZZLE_DECLARE_PLUGIN_END;