Difference between revisions of "Delphi compatible LCG Random"

From Free Pascal wiki
Jump to navigationJump to search
(Categorization)
Line 2: Line 2:
 
Many Freepascal programmers also maintain sourcecode in Delphi.<br>
 
Many Freepascal programmers also maintain sourcecode in Delphi.<br>
 
Even if you have moved to Freepascal from Delphi you may have data that relies on Delphi's Random.<br>
 
Even if you have moved to Freepascal from Delphi you may have data that relies on Delphi's Random.<br>
Here are cross-platform functions that generate Delphi-identical pseudo-random numbers:
+
Here are cross-platform functions that generate Delphi-identical pseudo-random numbers given the same RandSeed:
 
<syntaxhighlight>
 
<syntaxhighlight>
 
unit lcg_random;
 
unit lcg_random;
Line 36: Line 36:
  
 
end.</syntaxhighlight>
 
end.</syntaxhighlight>
 
[[Category:Statistical algorithms]]
 
[[Category:Modelling and Simulation]]
 

Revision as of 18:54, 26 March 2017

Delphi compatible random numbers

Many Freepascal programmers also maintain sourcecode in Delphi.
Even if you have moved to Freepascal from Delphi you may have data that relies on Delphi's Random.
Here are cross-platform functions that generate Delphi-identical pseudo-random numbers given the same RandSeed:

unit lcg_random;
// Delphi compatible LCG random number generator routines for Freepascal.
// (c)2017, Thaddy de Koning. Use as you like
// Algorithm, Delphi multiplier and increment taken from:
// https://en.wikipedia.org/wiki/Linear_congruential_generator
// The default Delphi RandomSeed is determined as zero.
{$mode objfpc}

interface

function LCGRandom: extended; overload;inline;
function LCGRandom(const range:longint):longint;overload;inline;

implementation

function IM:cardinal;inline;
begin
  RandSeed := RandSeed * 134775813  + 1;
  Result := RandSeed;
end;

function LCGRandom: extended; overload;inline;
begin
  Result := IM * 2.32830643653870e-10;
end;

function LCGRandom(const range:longint):longint;overload;inline;
begin
  Result := IM * range shr 32;
end;

end.