-- | -- Module : Crypto.Number.Generate -- License : BSD-style -- Maintainer : Vincent Hanquez <vincent@snarc.org> -- Stability : experimental -- Portability : Good module Crypto.Number.Generate ( generateMax , generateBetween , generateOfSize ) where import Crypto.Number.Serialize import Crypto.Random.API import qualified Data.ByteString as B import Data.Bits ((.|.)) -- | generate a positive integer x, s.t. 0 <= x < m -- -- Note that depending on m value, the number distribution -- generated by this function is not necessarily uniform. generateMax :: CPRG g => g -> Integer -> (Integer, g) generateMax rng m = withRandomBytes rng (lengthBytes m) $ \bs -> os2ip bs `mod` m -- | generate a number between the inclusive bound [low,high]. generateBetween :: CPRG g => g -> Integer -> Integer -> (Integer, g) generateBetween rng low high = (low + v, rng') where (v, rng') = generateMax rng (high - low + 1) -- | generate a positive integer of a specific size in bits. -- the number of bits need to be multiple of 8. It will always returns -- an integer that is close to 2^(1+bits/8) by setting the 2 highest bits to 1. generateOfSize :: CPRG g => g -> Int -> (Integer, g) generateOfSize rng bits = withRandomBytes rng (bits `div` 8) $ \bs -> os2ip $ snd $ B.mapAccumL (\acc w -> (0, w .|. acc)) 0xc0 bs