Editing Linear congruential generator (section)

== Sample code ==

===Python code===
The following is an implementation of an LCG in [[Python (programming language)|Python]], in the form of a [[Generator (computer programming)|generator]]:

<syntaxhighlight lang="python">
from collections.abc import Generator

def lcg(modulus: int, a: int, c: int, seed: int) -> Generator[int, None, None]:
    """Linear congruential generator."""
    while True:
        seed = (a * seed + c) % modulus
        yield seed
</syntaxhighlight>

===Haskell code===
The following is an implementation of an LCG in [[Haskell]] utilizing a [[Lazy evaluation#Working_with_infinite_data_structures|lazy evaluation]] strategy to generate an infinite stream of output values in a list:

<syntaxhighlight lang="haskell">
-- Allowing a generic choice for a, c, m and x_0
linearCongruentialGenerator :: Integer -> Integer -> Integer -> Integer -> [Integer]
linearCongruentialGenerator a c modulus seed = lcgacmx0
  where lcgacmx0 = seed : map (\x -> (a*x + c) `mod` modulus) lcgacmx0

-- Specific parameters can be easily specified (eg. Knuth's MMIX parameters):
mmixLCG :: Integer -> [Integer]
mmixLCG = linearCongruentialGenerator 6364136223846793005 1442695040888963407 (2^(64 ::Integer))
</syntaxhighlight>

===Free Pascal===
Free Pascal uses a [[Mersenne Twister]] as its default pseudo random number generator whereas Delphi uses a LCG. Here is a Delphi compatible example in [[Free Pascal]] based on the information in the table above. Given the same RandSeed value it generates the same sequence of random numbers as Delphi.

<syntaxhighlight lang="pascal">
unit lcg_random;
{$ifdef fpc}{$mode delphi}{$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;</syntaxhighlight>

Like all pseudorandom number generators, a LCG needs to store state and alter it each time it generates a new number. Multiple threads may access this state simultaneously causing a race condition. Implementations should use different state each with unique initialization for different threads to avoid equal sequences of random numbers on simultaneously executing threads.