Random Numbers in Ada

Ada’s Ada.Numerics.Float_Random and Ada.Numerics.Discrete_Random packages provide pseudorandom number generation.

with Ada.Text_IO;
with Ada.Numerics.Float_Random;
with Ada.Numerics.Discrete_Random;

procedure Random_Numbers is
   use Ada.Text_IO;
   
   package Random_Int is new Ada.Numerics.Discrete_Random (Integer);
   
   Gen : Ada.Numerics.Float_Random.Generator;
   Int_Gen : Random_Int.Generator;
begin
   -- For example, Random_Int.Random returns a random Integer n,
   -- 0 <= n < 100.
   Random_Int.Reset(Int_Gen);
   Put(Random_Int.Random(Int_Gen, 0, 99)'Image & ",");
   Put_Line(Random_Int.Random(Int_Gen, 0, 99)'Image);

   -- Ada.Numerics.Float_Random.Random returns a Float f,
   -- 0.0 <= f < 1.0.
   Ada.Numerics.Float_Random.Reset(Gen);
   Put_Line(Ada.Numerics.Float_Random.Random(Gen)'Image);

   -- This can be used to generate random floats in
   -- other ranges, for example 5.0 <= f' < 10.0.
   Put(Float'Image((Ada.Numerics.Float_Random.Random(Gen) * 5.0) + 5.0) & ",");
   Put_Line(Float'Image((Ada.Numerics.Float_Random.Random(Gen) * 5.0) + 5.0));

   -- If you want a known seed, you can use Reset with a specific seed value.
   Ada.Numerics.Float_Random.Reset(Gen, 42);
   Random_Int.Reset(Int_Gen, 1024);
   
   Put(Random_Int.Random(Int_Gen, 0, 99)'Image & ",");
   Put_Line(Random_Int.Random(Int_Gen, 0, 99)'Image);

   -- Using the same seed will produce the same sequence of random numbers.
   Ada.Numerics.Float_Random.Reset(Gen, 42);
   Random_Int.Reset(Int_Gen, 1024);
   
   Put(Random_Int.Random(Int_Gen, 0, 99)'Image & ",");
   Put_Line(Random_Int.Random(Int_Gen, 0, 99)'Image);
end Random_Numbers;

To run the program, save it as random_numbers.adb and use the Ada compiler (e.g., GNAT):

$ gnatmake random_numbers.adb
$ ./random_numbers
 68, 56
 8.09022814E-01
 5.84012508E+00, 6.93705630E+00
 94, 49
 94, 49

Some of the generated numbers may be different when you run the sample.

See the Ada Reference Manual, specifically the Ada.Numerics.Float_Random and Ada.Numerics.Discrete_Random packages, for references on other random quantities that Ada can provide.

In Ada, we use separate packages for generating random floating-point numbers (Ada.Numerics.Float_Random) and random integers (Ada.Numerics.Discrete_Random). The Discrete_Random package is generic and needs to be instantiated with the desired integer type.

Unlike the original example, Ada doesn’t provide a built-in PCG (Permuted Congruential Generator). Instead, we demonstrate how to use a specific seed to get reproducible random sequences, which is conceptually similar to creating a new source with a known seed.

Time Formatting Parsing in Ada

Number Parsing in Ada

Learn X By Example

Title here

Random Numbers in Ada