unit MATHUTYS;

interface

const MUID = '(c) J R Stockton  www.merlyn.demon.co.uk  >= 2008-03-18' ;

// These have a 64-bit sequence; System.random is 32-bit
// Effective randomness must be verified
// These are inadequate for crypto; seek "Random" Web sites
var RandSeed64 : UInt64 ;
procedure Randomise64 ;
function Random64 : extended ; overload ;
function Random64(const UI64 : UInt64) : UInt64 ; overload ;

implementation

uses Windows ;

{$OVERFLOWCHECKS ON} {$RANGECHECKS ON}

const
Factor = 6364136223846793005 { Said to be OK by Knuth } ;
HalfTo64 = 1.0 / (65536.0 * 65536.0 * 65536.0 * 65536.0) ;

procedure Randomise64 ;
begin
  { B := } QueryPerformanceCounter(Int64(RandSeed64)) ;
  end {Randomise64} ;

function Random64 : extended ; overload ;
begin
  {$OVERFLOWCHECKS OFF} {$RANGECHECKS OFF}
  RandSeed64 := RandSeed64*Factor + 1 ;
  {$RANGECHECKS ON} {$OVERFLOWCHECKS ON} 
  Result := RandSeed64*HalfTo64 ;
  end {Random64} ;

function Random64(const UI64 : UInt64) : UInt64 ; overload ;
begin
  Result := Trunc((Random64)*UI64) ;
  end {Random64} ;


end.