blob: c076956b43505a750ff3e5261fdd285d5d22757d (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
|
module T18730_A where
import Control.Monad (ap)
import Data.Word
import Data.Bits
newtype Gen a = MkGen
{ -- | Run the generator on a particular seed.
-- If you just want to get a random value out, consider using 'generate'.
unGen :: QCGen -> Int -> a
}
instance Functor Gen where
fmap f (MkGen h) =
MkGen (\r n -> f (h r n))
instance Applicative Gen where
pure x =
MkGen (\_ _ -> x)
(<*>) = ap
instance Monad Gen where
return = pure
MkGen m >>= k =
MkGen
( \r n ->
case split r of
(r1, r2) ->
let MkGen m' = k (m r1 n)
in m' r2 n
)
(>>) = (*>)
data QCGen = QCGen !Word64 !Word64
split :: QCGen -> (QCGen, QCGen)
split (QCGen seed gamma) =
(QCGen seed'' gamma, QCGen seed' (mixGamma seed''))
where
seed' = seed + gamma
seed'' = seed' + gamma
-- This piece appears to be critical
mixGamma :: Word64 -> Word64
mixGamma z0 =
if z0 >= 24
then z0
else z0 `xor` 0xaaaaaaaaaaaaaaaa
|
