Initial commit of Ben's raytracer

real/ben-raytrace/Random/Lehmer64.hs

+{-# LANGUAGE CPP #-}
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE UndecidableInstances #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE UnboxedTuples #-}
+{-# LANGUAGE MagicHash #-}
+{-# OPTIONS_GHC -fobject-code #-}
+
+module Random.Lehmer64 (GenState, mkGenState) where
+
+import System.Random.Stateful
+import GHC.Word
+import GHC.Prim (timesWord2#)
+
+type GenState = Lehmer64State
+
+mkGenState :: Word64 -> GenState
+mkGenState x = Lehmer64State x x
+
+data Lehmer64State = Lehmer64State !Word64 !Word64
+
+timesWord2 :: Word -> Word -> (Word, Word)
+timesWord2 (W# a) (W# b) =
+  case timesWord2# a b of (# x, y #) -> (W# x, W# y)
+
+instance RandomGen Lehmer64State where
+  split = error "Lehmer64 is not splittable"
+  genWord64 (Lehmer64State h l) =
+    let c = 0xda94042e4dd58b5
+        (!x, !y) = timesWord2 (fromIntegral c) (fromIntegral l)
+        l' = fromIntegral y
+        h' = fromIntegral x + h * c
+    in (h, Lehmer64State h' l')