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------------------------------------------------------------------------------ --- Library for pseudo-random number generation in Curry. --- --- This library provides operations for generating pseudo-random --- number sequences. --- For any given seed, the sequences generated by the operations --- in this module should be **identical** to the sequences --- generated by the `java.util.Random package`. --- ------------------------------------------------------------------------------ --- The KiCS2 implementation is based on an algorithm taken from --- <http://en.wikipedia.org/wiki/Random_number_generation>. --- There is an assumption that all operations are implicitly --- executed mod 2^32 (unsigned 32-bit integers) !!! --- GHC computes between -2^29 and 2^29-1, thus the sequence --- is NOT as random as one would like. --- --- m_w = <choose-initializer>; /* must not be zero */ --- m_z = <choose-initializer>; /* must not be zero */ --- --- uint get_random() --- { --- m_z = 36969 * (m_z & 65535) + (m_z >> 16); --- m_w = 18000 * (m_w & 65535) + (m_w >> 16); --- return (m_z << 16) + m_w; /* 32-bit result */ --- } --- ------------------------------------------------------------------------------ --- The PAKCS implementation is a linear congruential pseudo-random number --- generator described in --- Donald E. Knuth, _The Art of Computer Programming_, --- Volume 2: _Seminumerical Algorithms_, section 3.2.1. --- ------------------------------------------------------------------------------ --- @author Sergio Antoy (with extensions by Michael Hanus) --- @version June 2017 ------------------------------------------------------------------------------ {-# LANGUAGE CPP #-} module System.Random ( nextInt, nextIntRange, nextBoolean, getRandomSeed , shuffle ) where import System ( getCPUTime ) import Time ( CalendarTime(..), getClockTime, toUTCTime ) ------------------------------------------------------------------ -- Private Operations ------------------------------------------------------------------ -- a few constants multiplier :: Int multiplier = 25214903917 addend :: Int addend = 11 powermask :: Int powermask = 48 mask :: Int mask = 281474976710656 -- 2^powermask intsize :: Int intsize = 32 intspan :: Int intspan = 4294967296 -- 2^intsize intlimit :: Int intlimit = 2147483648 -- 2^(intsize-1) -- the basic sequence of random values sequence :: Int -> [Int] sequence seed = next : sequence next where next = nextseed seed -- auxiliary private operations nextseed :: Int -> Int nextseed seed = (seed * multiplier + addend) `rem` mask xor :: Int -> Int -> Int xor x y = if (x==0) && (y==0) then 0 else lastBit + 2 * restBits where lastBit = if (x `rem` 2) == (y `rem` 2) then 0 else 1 restBits = xor (x `quot` 2) (y `quot` 2) power :: Int -> Int -> Int power base exp = binary 1 base exp where binary x b e = if (e == 0) then x else binary (x * if (e `rem` 2 == 1) then b else 1) (b * b) (e `quot` 2) nextIntBits :: Int -> Int -> [Int] nextIntBits seed bits = map adjust list where init = (xor seed multiplier) `rem` mask list = sequence init shift = power 2 (powermask - bits) adjust x = if arg > intlimit then arg - intspan else arg where arg = (x `quot` shift) `rem` intspan ------------------------------------------------------------------ -- Public Operations ------------------------------------------------------------------ --- Returns a sequence of pseudorandom, integer values. --- --- @param seed - The seed of the random sequence. nextInt :: Int -> [Int] nextInt seed = nextIntBits seed intsize --- Returns a pseudorandom sequence of values --- between 0 (inclusive) and the specified value (exclusive). --- --- @param seed - The seed of the random sequence. --- @param n - The bound on the random number to be returned. --- Must be positive. nextIntRange :: Int -> Int -> [Int] nextIntRange seed n | n>0 = if power_of_2 n then map adjust_a seq else map adjust_b (filter adjust_c seq) where seq = nextIntBits seed (intsize - 1) adjust_a x = (n * x) `quot` intlimit adjust_b x = x `rem` n adjust_c x = x - (x `rem` n) + (n - 1) >= 0 power_of_2 k = k == 2 || k > 2 && k `rem` 2 == 0 && power_of_2 (k `quot` 2) --- Returns a pseudorandom sequence of boolean values. --- --- @param seed - The seed of the random sequence. nextBoolean :: Int -> [Bool] nextBoolean seed = map (/= 0) (nextIntBits seed 1) --- Returns a time-dependent integer number as a seed for really random numbers. --- Should only be used as a seed for pseudorandom number sequence --- and not as a random number since the precision is limited to milliseconds getRandomSeed :: IO Int getRandomSeed = getClockTime >>= \time -> getCPUTime >>= \msecs -> let (CalendarTime y mo d h m s _) = toUTCTime time in return ((y+mo+d+h+(m+1)*(s+1)*(msecs+1)) `rem` mask) --- Computes a random permutation of the given list. --- --- @param rnd random seed --- @param l lists to shuffle --- @return shuffled list --- shuffle :: Int -> [a] -> [a] shuffle rnd xs = shuffleWithLen (nextInt rnd) (length xs) xs shuffleWithLen :: [Int] -> Int -> [a] -> [a] shuffleWithLen [] _ _ = error "Internal error in Random.shuffleWithLen" shuffleWithLen (r:rs) len xs | len == 0 = [] | otherwise = z : shuffleWithLen rs (len-1) (ys++zs) where (ys,z:zs) = splitAt (abs r `rem` len) xs {- Simple tests and examples testInt = take 20 (nextInt 0) testIntRange = take 120 (nextIntRange 0 6) testBoolean = take 20 (nextBoolean 0) reallyRandom = do seed <- getRandomSeed putStrLn (show (take 20 (nextIntRange seed 100))) -} |