src/rand.rs

// Copyright (C) 2018-2019, Cloudflare, Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
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//
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//       this list of conditions and the following disclaimer.
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//     * Redistributions in binary form must reproduce the above copyright
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// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
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pub fn rand_bytes(buf: &mut [u8]) {
    unsafe {
        RAND_bytes(buf.as_mut_ptr(), buf.len());
    }
}

pub fn rand_u8() -> u8 {
    let mut buf = [0; 1];

    rand_bytes(&mut buf);

    buf[0]
}

pub fn rand_u64() -> u64 {
    let mut buf = [0; 8];

    rand_bytes(&mut buf);

    u64::from_ne_bytes(buf)
}

pub fn rand_u64_uniform(max: u64) -> u64 {
    let chunk_size = u64::max_value() / max;
    let end_of_last_chunk = chunk_size * max;

    let mut r = rand_u64();

    while r >= end_of_last_chunk {
        r = rand_u64();
    }

    r / chunk_size
}

extern {
    fn RAND_bytes(buf: *mut u8, len: libc::size_t) -> libc::c_int;
}