b64-ct 0.1.3

Fast and secure Base64 encoding/decoding. This crate provides an implementation of Base64 encoding/decoding that is designed to be resistant against software side-channel attacks (such as timing & cache attacks), see the documentation for details. On certain platforms it also uses SIMD making it very fast. This makes it suitable for e.g. decoding cryptographic private keys in PEM format. The API is very similar to the base64 implementation in the old rustc-serialize crate, making it easy to use in existing projects.
Documentation 
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/* Copyright (c) Fortanix, Inc.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

use rand::{distributions::Distribution, Rng};

struct Base64;

impl Distribution<u8> for Base64 {
    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> u8 {
        crate::misc::LUT_STANDARD[(rng.next_u32() & 0x3f) as usize]
    }
}

pub fn rand_base64_size(s: usize) -> std::vec::Vec<u8> {
    rand::thread_rng().sample_iter(&Base64).take(s).collect()
}

// `with_cartesian_products!(m (a b) (c d));` expands to `m!(a c); m!(a d); m!(b c); m!(b d);`.
#[macro_export]
macro_rules! with_cartesian_products {
    (@$m:ident $acc:tt ($($choice:tt)*) $rest:tt) => {
        $(with_cartesian_products!(@$rest $acc $choice $m);)*
    };
    (@() ($($acc:tt)*) $choice:tt $m:ident) => {
        $m!($($acc)* $choice);
    };
    (@($next:tt $($rest:tt)*) ($($acc:tt)*) $choice:tt $m:ident) => {
        with_cartesian_products!(@$m ($($acc)* $choice) $next ($($rest)*));
    };
    ($m:ident $next:tt $($rest:tt)*) => {
        with_cartesian_products!(@$m () $next ($($rest)*));
    };
}

#[macro_export]
macro_rules! generate_tests {
    (
        $_a:ident<$a:ident>: { $($(#[$am:meta])* $an:ident, $at:expr;)* },
        $_b:ident<$b:ident>: { $($(#[$bm:meta])* $bn:ident, $bt:expr;)* },
        tests: { $($tn:ident,)* },
    ) => {
        with_cartesian_products!( generate_tests ((@ $a $b)) ($($tn)*) ($(($(#[$am])* $an, $at))*) ($(($(#[$bm])*$bn, $bt))*) );
    };
    ((@ $a:ident $b:ident) $tn:ident ($(#[$am:meta])* $an:ident, $at:expr) ($(#[$bm:meta])* $bn:ident, $bt:expr)) => {
        paste::item! {
            $(#[$am])*
            $(#[$bm])*
            #[test]
            #[allow(non_snake_case)]
            fn [< $tn _ $a $an _ $b $bn >]() {
                $tn($at, $bt);
            }
        }
    }
}