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// Copyright 2019 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
use std::fs::File;
use std::io::{self, Read};
/// A simple prng based on a Linear congruential generator
/// https://en.wikipedia.org/wiki/Linear_congruential_generator
pub struct SimpleRng {
seed: u64,
}
impl SimpleRng {
/// Create a new SimpleRng
pub fn new(seed: u64) -> SimpleRng {
SimpleRng { seed }
}
/// Generate random u64
pub fn rng(&mut self) -> u64 {
// a simple Linear congruential generator
let a: u64 = 6364136223846793005;
let c: u64 = 1442695040888963407;
self.seed = a.wrapping_mul(self.seed).wrapping_add(c);
self.seed
}
}
/// Samples `/dev/urandom` and generates a random ASCII string of length `len`
pub fn urandom_str(len: usize) -> io::Result<String> {
const ASCII_CHARS: &'static [u8] = b"
ABCDEFGHIJKLMNOPQRSTUVWXYZ\
abcdefghijklmnopqrstuvwxyz\
0123456789";
File::open("/dev/urandom")?
.bytes()
.map(|b| b.map(|b| ASCII_CHARS[b as usize % ASCII_CHARS.len()] as char))
.take(len)
.collect::<io::Result<String>>()
}
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