Description

X'Compose(Fraction : X, Exponent : Integer) is an Ada attribute where X is any floating point type.

Floating point types are represented as:

${\displaystyle sign\times mantissa\times radix^{exponent}}$

where

sign is 1 or -1

mantissa is a fraction in base radix

radix is the hardware radix (usually 2)

exponent is an integer

'Compose(Fraction, Exponent) returns the floating point number Fraction with the exponent replaced with Exponent.

Example

with Ada.Text_IO;

procedure Compose is

   package T_IO renames Ada.Text_IO;
   package F_IO is new  Ada.Text_IO.Float_IO (Float);
   
   X : Float := 1.0;
begin
   T_IO.Put ("                   X = ");
   F_IO.Put(Item => X, Exp => 0);
   T_IO.New_Line;
   
   for Exp in -2..2 loop
      T_IO.Put ("Float'Compose(X, " & Integer'Image(Exp) & ") = ");
      F_IO.Put(Item => Float'Compose(X, Exp), Exp => 0);
      T_IO.New_Line;
   end loop;
   
end Compose;

The output with GNAT 4.6 on the x86-64 architecture is:

                   X =  1.00000
Float'Compose(X, -2) =  0.12500
Float'Compose(X, -1) =  0.25000
Float'Compose(X,  0) =  0.50000
Float'Compose(X,  1) =  1.00000
Float'Compose(X,  2) =  2.00000

See also