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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT RUN-TIME COMPONENTS --
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4 -- --
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5 -- S Y S T E M . R A N D O M _ N U M B E R S --
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6 -- --
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7 -- S p e c --
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8 -- --
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131
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9 -- Copyright (C) 2007-2018, Free Software Foundation, Inc. --
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111
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10 -- --
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11 -- GNAT is free software; you can redistribute it and/or modify it under --
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12 -- terms of the GNU General Public License as published by the Free Soft- --
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13 -- ware Foundation; either version 3, or (at your option) any later ver- --
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14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
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17 -- --
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18 -- As a special exception under Section 7 of GPL version 3, you are granted --
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19 -- additional permissions described in the GCC Runtime Library Exception, --
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20 -- version 3.1, as published by the Free Software Foundation. --
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21 -- --
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22 -- You should have received a copy of the GNU General Public License and --
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23 -- a copy of the GCC Runtime Library Exception along with this program; --
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24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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25 -- <http://www.gnu.org/licenses/>. --
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26 -- --
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27 -- GNAT was originally developed by the GNAT team at New York University. --
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28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
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29 -- --
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30 ------------------------------------------------------------------------------
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31
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32 -- Extended pseudo-random number generation
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33
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34 -- This package provides a type representing pseudo-random number generators,
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35 -- and subprograms to extract various uniform distributions of numbers
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36 -- from them. It also provides types for representing initialization values
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37 -- and snapshots of internal generator state, which permit reproducible
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38 -- pseudo-random streams.
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39
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40 -- The generator currently provided by this package has an extremely long
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41 -- period (at least 2**19937-1), and passes the Big Crush test suite, with the
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42 -- exception of the two linear complexity tests. Therefore, it is suitable
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43 -- for simulations, but should not be used as a cryptographic pseudo-random
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44 -- source without additional processing.
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45
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46 -- Note: this package is in the System hierarchy so that it can be directly
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47 -- used by other predefined packages. User access to this package is via
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48 -- the package GNAT.Random_Numbers (file g-rannum.ads), which also extends
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49 -- its capabilities. The interfaces are different so as to include in
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50 -- System.Random_Numbers only the definitions necessary to implement the
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51 -- standard random-number packages Ada.Numerics.Float_Random and
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52 -- Ada.Numerics.Discrete_Random.
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53
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54 -- Note: this package is marked SPARK_Mode Off, because functions Random work
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55 -- by side-effect to change the value of the generator, hence they should not
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56 -- be called from SPARK code.
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57
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58 with Interfaces;
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59
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60 package System.Random_Numbers with
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61 SPARK_Mode => Off
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62 is
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63 type Generator is limited private;
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64 -- Generator encodes the current state of a random number stream, it is
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65 -- provided as input to produce the next random number, and updated so
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66 -- that it is ready to produce the next one.
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67
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68 type State is private;
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69 -- A non-limited version of a Generator's internal state
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70
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71 function Random (Gen : Generator) return Float;
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72 function Random (Gen : Generator) return Long_Float;
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73 -- Return pseudo-random numbers uniformly distributed on [0.0 .. 1.0)
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74
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75 function Random (Gen : Generator) return Interfaces.Unsigned_32;
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76 function Random (Gen : Generator) return Interfaces.Unsigned_64;
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77 -- Return pseudo-random numbers uniformly distributed on T'First .. T'Last
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78 -- for builtin integer types.
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79
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80 generic
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81 type Result_Subtype is (<>);
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82 Default_Min : Result_Subtype := Result_Subtype'Val (0);
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83 function Random_Discrete
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84 (Gen : Generator;
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85 Min : Result_Subtype := Default_Min;
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86 Max : Result_Subtype := Result_Subtype'Last) return Result_Subtype;
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87 -- Returns pseudo-random numbers uniformly distributed on Min .. Max
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88
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89 generic
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90 type Result_Subtype is digits <>;
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91 function Random_Float (Gen : Generator) return Result_Subtype;
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92 -- Returns pseudo-random numbers uniformly distributed on [0 .. 1)
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93
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94 type Initialization_Vector is
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95 array (Integer range <>) of Interfaces.Unsigned_32;
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96 -- Provides the most general initialization values for a generator (used
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97 -- in Reset). In general, there is little point in providing more than
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98 -- a certain number of values (currently 624).
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99
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100 procedure Reset (Gen : Generator);
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101 -- Re-initialize the state of Gen from the time of day
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102
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103 procedure Reset (Gen : Generator; Initiator : Initialization_Vector);
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104 procedure Reset (Gen : Generator; Initiator : Interfaces.Integer_32);
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105 procedure Reset (Gen : Generator; Initiator : Interfaces.Unsigned_32);
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106 procedure Reset (Gen : Generator; Initiator : Integer);
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107 -- Re-initialize Gen based on the Initiator in various ways. Identical
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108 -- values of Initiator cause identical sequences of values.
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109
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110 procedure Reset (Gen : Generator; From_State : Generator);
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111 -- Causes the state of Gen to be identical to that of From_State; Gen
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112 -- and From_State will produce identical sequences of values subsequently.
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113
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114 procedure Reset (Gen : Generator; From_State : State);
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115 procedure Save (Gen : Generator; To_State : out State);
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116 -- The sequence
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117 -- Save (Gen2, S); Reset (Gen1, S)
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118 -- has the same effect as Reset (Gen2, Gen1).
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119
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120 procedure Reset (Gen : Generator; From_Image : String);
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121 function Image (Gen : Generator) return String;
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122 -- The call
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123 -- Reset (Gen2, Image (Gen1))
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124 -- has the same effect as Reset (Gen2, Gen1);
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125
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126 Max_Image_Width : constant := 11 * 624;
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127 -- Maximum possible length of result of Image (...)
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128
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129 function Image (Of_State : State) return String;
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130 -- A String representation of Of_State. Identical to the result of
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131 -- Image (Gen), if Of_State has been set with Save (Gen, Of_State).
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132
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133 function Value (Coded_State : String) return State;
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134 -- Inverse of Image on States
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135
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136 private
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137
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138 N : constant := 624;
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139 -- The number of 32-bit integers in the shift register
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140
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141 M : constant := 397;
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142 -- Feedback distance from the current position
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143
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144 subtype State_Val is Interfaces.Unsigned_32;
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145 type State is array (0 .. N - 1) of State_Val;
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146
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147 type Writable_Access (Self : access Generator) is limited null record;
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148 -- Auxiliary type to make Generator a self-referential type
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149
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150 type Generator is limited record
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151 Writable : Writable_Access (Generator'Access);
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152 -- This self reference allows functions to modify Generator arguments
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153
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154 S : State := (others => 0);
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155 -- The shift register, a circular buffer
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156
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157 I : Integer := N;
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158 -- Current starting position in shift register S (N means uninitialized)
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159 -- We should avoid using the identifier I here ???
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160 end record;
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161
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162 end System.Random_Numbers;
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