Difference between revisions of "Delphi compatible LCG Random"
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end; | end; | ||
+ | end.</syntaxhighlight> | ||
+ | <br> | ||
+ | A small demo | ||
+ | <syntaxhighlight> | ||
+ | program lcgdemo; | ||
+ | // Compile and run in both Delphi and FPC and compare the output. | ||
+ | // It is exactly the same | ||
+ | {$ifdef fpc}{$mode objfpc} | ||
+ | {$Macro on}{$define random := LCGRandom} | ||
+ | {$endif} | ||
+ | {$ifdef mswindows}{$apptype console}{$endif} | ||
+ | uses lcg_random; | ||
+ | |||
+ | var i:integer; | ||
+ | begin | ||
+ | RandSeed := 999; // default delphi randseed is zero | ||
+ | for i := 1 to 20 do | ||
+ | begin | ||
+ | write(Random(100):4); // Delphi: Random FPC:LCGRandom | ||
+ | if i mod 5 = 0then writeln; | ||
+ | end; | ||
+ | |||
+ | RandSeed := 999; // default delphi randseed is zero | ||
+ | for i := 1 to 20 do | ||
+ | begin | ||
+ | write(Random:4:8,' ');// Delphi: Random FPC:LCGRandom | ||
+ | if i mod 5 = 0 then writeln; | ||
+ | end; | ||
+ | Readln; | ||
end.</syntaxhighlight> | end.</syntaxhighlight> | ||
[[Category:Statistical algorithms]] | [[Category:Statistical algorithms]] | ||
[[Category:Modelling and Simulation]] | [[Category:Modelling and Simulation]] |
Revision as of 20:59, 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.
{$ifdef fpc}{$mode objfpc}{$endif}
interface
function LCGRandom: extended; overload;inline;
function LCGRandom(const range:longint):longint;overload;inline;
implementation
function IM:cardinal;inline;
begin
RandSeed := RandSeed * 134775813 + 1;
Result := RandSeed;
end;
function LCGRandom: extended; overload;inline;
begin
Result := IM * 2.32830643653870e-10;
end;
function LCGRandom(const range:longint):longint;overload;inline;
begin
Result := IM * range shr 32;
end;
end.
A small demo
program lcgdemo;
// Compile and run in both Delphi and FPC and compare the output.
// It is exactly the same
{$ifdef fpc}{$mode objfpc}
{$Macro on}{$define random := LCGRandom}
{$endif}
{$ifdef mswindows}{$apptype console}{$endif}
uses lcg_random;
var i:integer;
begin
RandSeed := 999; // default delphi randseed is zero
for i := 1 to 20 do
begin
write(Random(100):4); // Delphi: Random FPC:LCGRandom
if i mod 5 = 0then writeln;
end;
RandSeed := 999; // default delphi randseed is zero
for i := 1 to 20 do
begin
write(Random:4:8,' ');// Delphi: Random FPC:LCGRandom
if i mod 5 = 0 then writeln;
end;
Readln;
end.