Remove RandomNumberGenerator (#9198)

* Remove RandomNumberGenerator

This is not used in Substrate/Polkadot. If someone else needs it, they
can copy the code or use chacha.

* 

substrate/primitives/runtime/src/lib.rs

@@ -54,7 +54,6 @@ pub mod offchain;
 pub mod testing;
 pub mod traits;
 pub mod transaction_validity;
-pub mod random_number_generator;
 mod runtime_string;
 mod multiaddress;
 pub mod runtime_logger;
@@ -85,8 +84,6 @@ pub use sp_arithmetic::helpers_128bit;
 /// Re-export big_uint stuff.
 pub use sp_arithmetic::biguint;
 
-pub use random_number_generator::RandomNumberGenerator;
-
 pub use either::Either;
 
 /// An abstraction over justification for a block's validity under a consensus algorithm.

substrate/primitives/runtime/src/random_number_generator.rs

-// This file is part of Substrate.
-
-// Copyright (C) 2017-2021 Parity Technologies (UK) Ltd.
-// SPDX-License-Identifier: Apache-2.0
-
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-// 	http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-//! A simple pseudo random number generator that allows a stream of random numbers to be efficiently
-//! created from a single initial seed hash.
-
-use codec::{Encode, Decode};
-use crate::traits::{Hash, TrailingZeroInput};
-
-/// Pseudo-random number streamer. This retains the state of the random number stream. It's as
-/// secure as the combination of the seed with which it is constructed and the hash function it uses
-/// to cycle elements.
-///
-/// It can be saved and later reloaded using the Codec traits.
-///
-/// (It is recommended to use the `rand_chacha` crate as an alternative to this where possible.)
-///
-/// Example:
-/// ```
-/// use sp_runtime::traits::{Hash, BlakeTwo256};
-/// use sp_runtime::RandomNumberGenerator;
-/// let random_seed = BlakeTwo256::hash(b"Sixty-nine");
-/// let mut rng = <RandomNumberGenerator<BlakeTwo256>>::new(random_seed);
-/// assert_eq!(rng.pick_u32(100), 59);
-/// assert_eq!(rng.pick_item(&[1, 2, 3]), Some(&1));
-/// ```
-///
-/// This can use any cryptographic `Hash` function as the means of entropy-extension, and avoids
-/// needless extensions of entropy.
-///
-/// If you're persisting it over blocks, be aware that the sequence will start to repeat. This won't
-/// be a practical issue unless you're using tiny hash types (e.g. 64-bit) and pulling hundred of
-/// megabytes of data from it.
-#[derive(Encode, Decode)]
-pub struct RandomNumberGenerator<Hashing: Hash> {
-	current: Hashing::Output,
-	offset: u32,
-}
-
-impl<Hashing: Hash> RandomNumberGenerator<Hashing> {
-	/// A new source of random data.
-	pub fn new(seed: Hashing::Output) -> Self {
-		Self {
-			current: seed,
-			offset: 0,
-		}
-	}
-
-	fn offset(&self) -> usize { self.offset as usize }
-
-	/// Returns a number at least zero, at most `max`.
-	pub fn pick_u32(&mut self, max: u32) -> u32 {
-		let needed = (4 - max.leading_zeros() / 8) as usize;
-		let top = ((1 << (needed as u64 * 8)) / (max as u64 + 1) * (max as u64 + 1) - 1) as u32;
-		loop {
-			if self.offset() + needed > self.current.as_ref().len() {
-				// rehash
-				self.current = <Hashing as Hash>::hash(self.current.as_ref());
-				self.offset = 0;
-			}
-			let data = &self.current.as_ref()[self.offset()..self.offset() + needed];
-			self.offset += needed as u32;
-			let raw = u32::decode(&mut TrailingZeroInput::new(data)).unwrap_or(0);
-			if raw <= top {
-				break if max < u32::MAX {
-					raw % (max + 1)
-				} else {
-					raw
-				}
-			}
-		}
-	}
-
-	/// Returns a number at least zero, at most `max`.
-	///
-	/// This returns a `usize`, but internally it only uses `u32` so avoid consensus problems.
-	pub fn pick_usize(&mut self, max: usize) -> usize {
-		self.pick_u32(max as u32) as usize
-	}
-
-	/// Pick a random element from an array of `items`.
-	///
-	/// This is guaranteed to return `Some` except in the case that the given array `items` is
-	/// empty.
-	pub fn pick_item<'a, T>(&mut self, items: &'a [T]) -> Option<&'a T> {
-		if items.is_empty() {
-			None
-		} else {
-			Some(&items[self.pick_usize(items.len() - 1)])
-		}
-	}
-}
-
-#[cfg(test)]
-mod tests {
-	use super::RandomNumberGenerator;
-	use crate::traits::{Hash, BlakeTwo256};
-
-	#[test]
-	fn does_not_panic_on_max() {
-		let seed = BlakeTwo256::hash(b"Fourty-two");
-		let _random = RandomNumberGenerator::<BlakeTwo256>::new(seed).pick_u32(u32::MAX);
-	}
-}