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Fix issue 21609 - LinearCongruentialEngine fails for m = 0

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Cameron Ross 2021-02-04 00:25:53 -04:00 • committed by The Dlang Bot
parent d7b98833ce
commit df10d1e331
1 changed files with 31 additions and 2 deletions
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33
std/random.d
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@ -425,7 +425,7 @@ template isSeedable(Rng)
}
/**
Linear Congruential generator.
Linear Congruential generator. When m = 0, no modulus is used.
*/
struct LinearCongruentialEngine(UIntType, UIntType a, UIntType c, UIntType m)
if (isUnsigned!UIntType)
@ -603,7 +603,15 @@ Always `false` (random generators are infinite ranges).
*/
enum bool empty = false;
private UIntType _x = m ? (a + c) % m : (a + c);
// https://issues.dlang.org/show_bug.cgi?id=21610
static if (m)
{
private UIntType _x = (a + c) % m;
}
else
{
private UIntType _x = a + c;
}
}
/// Declare your own linear congruential engine
@ -628,6 +636,27 @@ Always `false` (random generators are infinite ranges).
auto n = rnd.front; // different across runs
}
/// Declare your own linear congruential engine
@safe unittest
{
// Visual C++'s LCG
alias MSVCLCG = LinearCongruentialEngine!(uint, 214013, 2531011, 0);
// seed with a constant
auto rnd = MSVCLCG(1);
auto n = rnd.front; // same for each run
assert(n == 2745024);
}
// Ensure that unseeded LCGs produce correct values
@safe unittest
{
alias LGE = LinearCongruentialEngine!(uint, 10000, 19682, 19683);
LGE rnd;
assert(rnd.front == 9999);
}
/**
Define $(D_PARAM LinearCongruentialEngine) generators with well-chosen
parameters. `MinstdRand0` implements Park and Miller's "minimal