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-- |
-- Module : Number.Generate
-- License : BSD-style
-- Maintainer : Vincent Hanquez <vincent@snarc.org>
-- Stability : experimental
-- Portability : Good
module Number.Generate
( generateMax
, generateBetween
, generateOfSize
) where
import Number.Serialize
import Crypto.Random
import qualified Data.ByteString as B
import Data.Bits ((.|.))
-- | generate a positive integer between 0 and m.
-- using as many bytes as necessary to the same size as m, that are converted to integer.
generateMax :: CryptoRandomGen g => g -> Integer -> Either GenError (Integer, g)
generateMax rng m = case genBytes (lengthBytes m) rng of
Left err -> Left err
Right (bs, rng') -> Right (os2ip bs `mod` m, rng')
-- | generate a number between the inclusive bound [low,high].
generateBetween :: CryptoRandomGen g => g -> Integer -> Integer -> Either GenError (Integer, g)
generateBetween rng low high = case generateMax rng (high - low + 1) of
Left err -> Left err
Right (v, rng') -> Right (low + v, rng')
-- | 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 2^(1+bits/8) by setting the 2 highest bits to 1.
generateOfSize :: CryptoRandomGen g => g -> Int -> Either GenError (Integer, g)
generateOfSize rng bits = case genBytes (bits `div` 8) rng of
Left err -> Left err
Right (bs, rng') -> Right (os2ip $ snd $ B.mapAccumL (\acc w -> (0, w .|. acc)) 0xc0 bs, rng')
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