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</pre><pre class="rust"><code><span class="comment">// Copyright 2018 Developers of the Rand project.
//
// Licensed under the Apache License, Version 2.0 &lt;LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0&gt; or the MIT license
// &lt;LICENSE-MIT or https://opensource.org/licenses/MIT&gt;, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
</span><span class="doccomment">//! The implementations of the `Standard` distribution for other built-in types.
</span><span class="kw">use </span>core::char;
<span class="kw">use </span>core::num::Wrapping;
<span class="attribute">#[cfg(feature = <span class="string">&quot;alloc&quot;</span>)]
</span><span class="kw">use </span>alloc::string::String;
<span class="kw">use </span><span class="kw">crate</span>::distributions::{Distribution, Standard, Uniform};
<span class="attribute">#[cfg(feature = <span class="string">&quot;alloc&quot;</span>)]
</span><span class="kw">use </span><span class="kw">crate</span>::distributions::DistString;
<span class="kw">use </span><span class="kw">crate</span>::Rng;
<span class="attribute">#[cfg(feature = <span class="string">&quot;serde1&quot;</span>)]
</span><span class="kw">use </span>serde::{Serialize, Deserialize};
<span class="attribute">#[cfg(feature = <span class="string">&quot;min_const_gen&quot;</span>)]
</span><span class="kw">use </span>core::mem::{<span class="self">self</span>, MaybeUninit};
<span class="comment">// ----- Sampling distributions -----
</span><span class="doccomment">/// Sample a `u8`, uniformly distributed over ASCII letters and numbers:
/// a-z, A-Z and 0-9.
///
/// # Example
///
/// ```
/// use rand::{Rng, thread_rng};
/// use rand::distributions::Alphanumeric;
///
/// let mut rng = thread_rng();
/// let chars: String = (0..7).map(|_| rng.sample(Alphanumeric) as char).collect();
/// println!(&quot;Random chars: {}&quot;, chars);
/// ```
///
/// The [`DistString`] trait provides an easier method of generating
/// a random `String`, and offers more efficient allocation:
/// ```
/// use rand::distributions::{Alphanumeric, DistString};
/// let string = Alphanumeric.sample_string(&amp;mut rand::thread_rng(), 16);
/// println!(&quot;Random string: {}&quot;, string);
/// ```
///
/// # Passwords
///
/// Users sometimes ask whether it is safe to use a string of random characters
/// as a password. In principle, all RNGs in Rand implementing `CryptoRng` are
/// suitable as a source of randomness for generating passwords (if they are
/// properly seeded), but it is more conservative to only use randomness
/// directly from the operating system via the `getrandom` crate, or the
/// corresponding bindings of a crypto library.
///
/// When generating passwords or keys, it is important to consider the threat
/// model and in some cases the memorability of the password. This is out of
/// scope of the Rand project, and therefore we defer to the following
/// references:
///
/// - [Wikipedia article on Password Strength](https://en.wikipedia.org/wiki/Password_strength)
/// - [Diceware for generating memorable passwords](https://en.wikipedia.org/wiki/Diceware)
</span><span class="attribute">#[derive(Debug, Clone, Copy)]
#[cfg_attr(feature = <span class="string">&quot;serde1&quot;</span>, derive(Serialize, Deserialize))]
</span><span class="kw">pub struct </span>Alphanumeric;
<span class="comment">// ----- Implementations of distributions -----
</span><span class="kw">impl </span>Distribution&lt;char&gt; <span class="kw">for </span>Standard {
<span class="attribute">#[inline]
</span><span class="kw">fn </span>sample&lt;R: Rng + <span class="question-mark">?</span>Sized&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, rng: <span class="kw-2">&amp;mut </span>R) -&gt; char {
<span class="comment">// A valid `char` is either in the interval `[0, 0xD800)` or
// `(0xDFFF, 0x11_0000)`. All `char`s must therefore be in
// `[0, 0x11_0000)` but not in the &quot;gap&quot; `[0xD800, 0xDFFF]` which is
// reserved for surrogates. This is the size of that gap.
</span><span class="kw">const </span>GAP_SIZE: u32 = <span class="number">0xDFFF </span>- <span class="number">0xD800 </span>+ <span class="number">1</span>;
<span class="comment">// Uniform::new(0, 0x11_0000 - GAP_SIZE) can also be used but it
// seemed slower.
</span><span class="kw">let </span>range = Uniform::new(GAP_SIZE, <span class="number">0x11_0000</span>);
<span class="kw">let </span><span class="kw-2">mut </span>n = range.sample(rng);
<span class="kw">if </span>n &lt;= <span class="number">0xDFFF </span>{
n -= GAP_SIZE;
}
<span class="kw">unsafe </span>{ char::from_u32_unchecked(n) }
}
}
<span class="doccomment">/// Note: the `String` is potentially left with excess capacity; optionally the
/// user may call `string.shrink_to_fit()` afterwards.
</span><span class="attribute">#[cfg(feature = <span class="string">&quot;alloc&quot;</span>)]
</span><span class="kw">impl </span>DistString <span class="kw">for </span>Standard {
<span class="kw">fn </span>append_string&lt;R: Rng + <span class="question-mark">?</span>Sized&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, rng: <span class="kw-2">&amp;mut </span>R, s: <span class="kw-2">&amp;mut </span>String, len: usize) {
<span class="comment">// A char is encoded with at most four bytes, thus this reservation is
// guaranteed to be sufficient. We do not shrink_to_fit afterwards so
// that repeated usage on the same `String` buffer does not reallocate.
</span>s.reserve(<span class="number">4 </span>* len);
s.extend(Distribution::&lt;char&gt;::sample_iter(<span class="self">self</span>, rng).take(len));
}
}
<span class="kw">impl </span>Distribution&lt;u8&gt; <span class="kw">for </span>Alphanumeric {
<span class="kw">fn </span>sample&lt;R: Rng + <span class="question-mark">?</span>Sized&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, rng: <span class="kw-2">&amp;mut </span>R) -&gt; u8 {
<span class="kw">const </span>RANGE: u32 = <span class="number">26 </span>+ <span class="number">26 </span>+ <span class="number">10</span>;
<span class="kw">const </span>GEN_ASCII_STR_CHARSET: <span class="kw-2">&amp;</span>[u8] = <span class="string">b&quot;ABCDEFGHIJKLMNOPQRSTUVWXYZ\
abcdefghijklmnopqrstuvwxyz\
0123456789&quot;</span>;
<span class="comment">// We can pick from 62 characters. This is so close to a power of 2, 64,
// that we can do better than `Uniform`. Use a simple bitshift and
// rejection sampling. We do not use a bitmask, because for small RNGs
// the most significant bits are usually of higher quality.
</span><span class="kw">loop </span>{
<span class="kw">let </span>var = rng.next_u32() &gt;&gt; (<span class="number">32 </span>- <span class="number">6</span>);
<span class="kw">if </span>var &lt; RANGE {
<span class="kw">return </span>GEN_ASCII_STR_CHARSET[var <span class="kw">as </span>usize];
}
}
}
}
<span class="attribute">#[cfg(feature = <span class="string">&quot;alloc&quot;</span>)]
</span><span class="kw">impl </span>DistString <span class="kw">for </span>Alphanumeric {
<span class="kw">fn </span>append_string&lt;R: Rng + <span class="question-mark">?</span>Sized&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, rng: <span class="kw-2">&amp;mut </span>R, string: <span class="kw-2">&amp;mut </span>String, len: usize) {
<span class="kw">unsafe </span>{
<span class="kw">let </span>v = string.as_mut_vec();
v.extend(<span class="self">self</span>.sample_iter(rng).take(len));
}
}
}
<span class="kw">impl </span>Distribution&lt;bool&gt; <span class="kw">for </span>Standard {
<span class="attribute">#[inline]
</span><span class="kw">fn </span>sample&lt;R: Rng + <span class="question-mark">?</span>Sized&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, rng: <span class="kw-2">&amp;mut </span>R) -&gt; bool {
<span class="comment">// We can compare against an arbitrary bit of an u32 to get a bool.
// Because the least significant bits of a lower quality RNG can have
// simple patterns, we compare against the most significant bit. This is
// easiest done using a sign test.
</span>(rng.next_u32() <span class="kw">as </span>i32) &lt; <span class="number">0
</span>}
}
<span class="macro">macro_rules! </span>tuple_impl {
<span class="comment">// use variables to indicate the arity of the tuple
</span>($(<span class="macro-nonterminal">$tyvar</span>:ident),* ) =&gt; {
<span class="comment">// the trailing commas are for the 1 tuple
</span><span class="kw">impl</span>&lt; $( <span class="macro-nonterminal">$tyvar </span>),* &gt;
Distribution&lt;( $( <span class="macro-nonterminal">$tyvar </span>),* , )&gt;
<span class="kw">for </span>Standard
<span class="kw">where </span>$( Standard: Distribution&lt;<span class="macro-nonterminal">$tyvar</span>&gt; ),*
{
<span class="attribute">#[inline]
</span><span class="kw">fn </span>sample&lt;R: Rng + <span class="question-mark">?</span>Sized&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, _rng: <span class="kw-2">&amp;mut </span>R) -&gt; ( $( <span class="macro-nonterminal">$tyvar </span>),* , ) {
(
<span class="comment">// use the $tyvar&#39;s to get the appropriate number of
// repeats (they&#39;re not actually needed)
</span>$(
_rng.gen::&lt;<span class="macro-nonterminal">$tyvar</span>&gt;()
),*
,
)
}
}
}
}
<span class="kw">impl </span>Distribution&lt;()&gt; <span class="kw">for </span>Standard {
<span class="attribute">#[allow(clippy::unused_unit)]
#[inline]
</span><span class="kw">fn </span>sample&lt;R: Rng + <span class="question-mark">?</span>Sized&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="kw">_</span>: <span class="kw-2">&amp;mut </span>R) -&gt; () {
()
}
}
<span class="macro">tuple_impl! </span>{A}
<span class="macro">tuple_impl! </span>{A, B}
<span class="macro">tuple_impl! </span>{A, B, C}
<span class="macro">tuple_impl! </span>{A, B, C, D}
<span class="macro">tuple_impl! </span>{A, B, C, D, E}
<span class="macro">tuple_impl! </span>{A, B, C, D, E, F}
<span class="macro">tuple_impl! </span>{A, B, C, D, E, F, G}
<span class="macro">tuple_impl! </span>{A, B, C, D, E, F, G, H}
<span class="macro">tuple_impl! </span>{A, B, C, D, E, F, G, H, I}
<span class="macro">tuple_impl! </span>{A, B, C, D, E, F, G, H, I, J}
<span class="macro">tuple_impl! </span>{A, B, C, D, E, F, G, H, I, J, K}
<span class="macro">tuple_impl! </span>{A, B, C, D, E, F, G, H, I, J, K, L}
<span class="attribute">#[cfg(feature = <span class="string">&quot;min_const_gen&quot;</span>)]
#[cfg_attr(doc_cfg, doc(cfg(feature = <span class="string">&quot;min_const_gen&quot;</span>)))]
</span><span class="kw">impl</span>&lt;T, <span class="kw">const </span>N: usize&gt; Distribution&lt;[T; N]&gt; <span class="kw">for </span>Standard
<span class="kw">where </span>Standard: Distribution&lt;T&gt;
{
<span class="attribute">#[inline]
</span><span class="kw">fn </span>sample&lt;R: Rng + <span class="question-mark">?</span>Sized&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, _rng: <span class="kw-2">&amp;mut </span>R) -&gt; [T; N] {
<span class="kw">let </span><span class="kw-2">mut </span>buff: [MaybeUninit&lt;T&gt;; N] = <span class="kw">unsafe </span>{ MaybeUninit::uninit().assume_init() };
<span class="kw">for </span>elem <span class="kw">in </span><span class="kw-2">&amp;mut </span>buff {
<span class="kw-2">*</span>elem = MaybeUninit::new(_rng.gen());
}
<span class="kw">unsafe </span>{ mem::transmute_copy::&lt;<span class="kw">_</span>, <span class="kw">_</span>&gt;(<span class="kw-2">&amp;</span>buff) }
}
}
<span class="attribute">#[cfg(not(feature = <span class="string">&quot;min_const_gen&quot;</span>))]
</span><span class="macro">macro_rules! </span>array_impl {
<span class="comment">// recursive, given at least one type parameter:
</span>{<span class="macro-nonterminal">$n</span>:expr, <span class="macro-nonterminal">$t</span>:ident, $(<span class="macro-nonterminal">$ts</span>:ident,)<span class="kw-2">*</span>} =&gt; {
<span class="macro">array_impl!</span>{(<span class="macro-nonterminal">$n </span>- <span class="number">1</span>), $(<span class="macro-nonterminal">$ts</span>,)<span class="kw-2">*</span>}
<span class="kw">impl</span>&lt;T&gt; Distribution&lt;[T; <span class="macro-nonterminal">$n</span>]&gt; <span class="kw">for </span>Standard <span class="kw">where </span>Standard: Distribution&lt;T&gt; {
<span class="attribute">#[inline]
</span><span class="kw">fn </span>sample&lt;R: Rng + <span class="question-mark">?</span>Sized&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, _rng: <span class="kw-2">&amp;mut </span>R) -&gt; [T; <span class="macro-nonterminal">$n</span>] {
[_rng.gen::&lt;<span class="macro-nonterminal">$t</span>&gt;(), $(_rng.gen::&lt;<span class="macro-nonterminal">$ts</span>&gt;()),<span class="kw-2">*</span>]
}
}
};
<span class="comment">// empty case:
</span>{<span class="macro-nonterminal">$n</span>:expr,} =&gt; {
<span class="kw">impl</span>&lt;T&gt; Distribution&lt;[T; <span class="macro-nonterminal">$n</span>]&gt; <span class="kw">for </span>Standard {
<span class="kw">fn </span>sample&lt;R: Rng + <span class="question-mark">?</span>Sized&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, _rng: <span class="kw-2">&amp;mut </span>R) -&gt; [T; <span class="macro-nonterminal">$n</span>] { [] }
}
};
}
<span class="attribute">#[cfg(not(feature = <span class="string">&quot;min_const_gen&quot;</span>))]
</span><span class="macro">array_impl! </span>{<span class="number">32</span>, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T,}
<span class="kw">impl</span>&lt;T&gt; Distribution&lt;<span class="prelude-ty">Option</span>&lt;T&gt;&gt; <span class="kw">for </span>Standard
<span class="kw">where </span>Standard: Distribution&lt;T&gt;
{
<span class="attribute">#[inline]
</span><span class="kw">fn </span>sample&lt;R: Rng + <span class="question-mark">?</span>Sized&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, rng: <span class="kw-2">&amp;mut </span>R) -&gt; <span class="prelude-ty">Option</span>&lt;T&gt; {
<span class="comment">// UFCS is needed here: https://github.com/rust-lang/rust/issues/24066
</span><span class="kw">if </span>rng.gen::&lt;bool&gt;() {
<span class="prelude-val">Some</span>(rng.gen())
} <span class="kw">else </span>{
<span class="prelude-val">None
</span>}
}
}
<span class="kw">impl</span>&lt;T&gt; Distribution&lt;Wrapping&lt;T&gt;&gt; <span class="kw">for </span>Standard
<span class="kw">where </span>Standard: Distribution&lt;T&gt;
{
<span class="attribute">#[inline]
</span><span class="kw">fn </span>sample&lt;R: Rng + <span class="question-mark">?</span>Sized&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, rng: <span class="kw-2">&amp;mut </span>R) -&gt; Wrapping&lt;T&gt; {
Wrapping(rng.gen())
}
}
<span class="attribute">#[cfg(test)]
</span><span class="kw">mod </span>tests {
<span class="kw">use super</span>::<span class="kw-2">*</span>;
<span class="kw">use </span><span class="kw">crate</span>::RngCore;
<span class="attribute">#[cfg(feature = <span class="string">&quot;alloc&quot;</span>)] </span><span class="kw">use </span>alloc::string::String;
<span class="attribute">#[test]
</span><span class="kw">fn </span>test_misc() {
<span class="kw">let </span>rng: <span class="kw-2">&amp;mut </span><span class="kw">dyn </span>RngCore = <span class="kw-2">&amp;mut </span><span class="kw">crate</span>::test::rng(<span class="number">820</span>);
rng.sample::&lt;char, <span class="kw">_</span>&gt;(Standard);
rng.sample::&lt;bool, <span class="kw">_</span>&gt;(Standard);
}
<span class="attribute">#[cfg(feature = <span class="string">&quot;alloc&quot;</span>)]
#[test]
</span><span class="kw">fn </span>test_chars() {
<span class="kw">use </span>core::iter;
<span class="kw">let </span><span class="kw-2">mut </span>rng = <span class="kw">crate</span>::test::rng(<span class="number">805</span>);
<span class="comment">// Test by generating a relatively large number of chars, so we also
// take the rejection sampling path.
</span><span class="kw">let </span>word: String = iter::repeat(())
.map(|()| rng.gen::&lt;char&gt;())
.take(<span class="number">1000</span>)
.collect();
<span class="macro">assert!</span>(!word.is_empty());
}
<span class="attribute">#[test]
</span><span class="kw">fn </span>test_alphanumeric() {
<span class="kw">let </span><span class="kw-2">mut </span>rng = <span class="kw">crate</span>::test::rng(<span class="number">806</span>);
<span class="comment">// Test by generating a relatively large number of chars, so we also
// take the rejection sampling path.
</span><span class="kw">let </span><span class="kw-2">mut </span>incorrect = <span class="bool-val">false</span>;
<span class="kw">for _ in </span><span class="number">0</span>..<span class="number">100 </span>{
<span class="kw">let </span>c: char = rng.sample(Alphanumeric).into();
incorrect |= !((<span class="string">&#39;0&#39;</span>..=<span class="string">&#39;9&#39;</span>).contains(<span class="kw-2">&amp;</span>c) ||
(<span class="string">&#39;A&#39;</span>..=<span class="string">&#39;Z&#39;</span>).contains(<span class="kw-2">&amp;</span>c) ||
(<span class="string">&#39;a&#39;</span>..=<span class="string">&#39;z&#39;</span>).contains(<span class="kw-2">&amp;</span>c) );
}
<span class="macro">assert!</span>(!incorrect);
}
<span class="attribute">#[test]
</span><span class="kw">fn </span>value_stability() {
<span class="kw">fn </span>test_samples&lt;T: Copy + core::fmt::Debug + PartialEq, D: Distribution&lt;T&gt;&gt;(
distr: <span class="kw-2">&amp;</span>D, zero: T, expected: <span class="kw-2">&amp;</span>[T],
) {
<span class="kw">let </span><span class="kw-2">mut </span>rng = <span class="kw">crate</span>::test::rng(<span class="number">807</span>);
<span class="kw">let </span><span class="kw-2">mut </span>buf = [zero; <span class="number">5</span>];
<span class="kw">for </span>x <span class="kw">in </span><span class="kw-2">&amp;mut </span>buf {
<span class="kw-2">*</span>x = rng.sample(<span class="kw-2">&amp;</span>distr);
}
<span class="macro">assert_eq!</span>(<span class="kw-2">&amp;</span>buf, expected);
}
test_samples(<span class="kw-2">&amp;</span>Standard, <span class="string">&#39;a&#39;</span>, <span class="kw-2">&amp;</span>[
<span class="string">&#39;\u{8cdac}&#39;</span>,
<span class="string">&#39;\u{a346a}&#39;</span>,
<span class="string">&#39;\u{80120}&#39;</span>,
<span class="string">&#39;\u{ed692}&#39;</span>,
<span class="string">&#39;\u{35888}&#39;</span>,
]);
test_samples(<span class="kw-2">&amp;</span>Alphanumeric, <span class="number">0</span>, <span class="kw-2">&amp;</span>[<span class="number">104</span>, <span class="number">109</span>, <span class="number">101</span>, <span class="number">51</span>, <span class="number">77</span>]);
test_samples(<span class="kw-2">&amp;</span>Standard, <span class="bool-val">false</span>, <span class="kw-2">&amp;</span>[<span class="bool-val">true</span>, <span class="bool-val">true</span>, <span class="bool-val">false</span>, <span class="bool-val">true</span>, <span class="bool-val">false</span>]);
test_samples(<span class="kw-2">&amp;</span>Standard, <span class="prelude-val">None </span><span class="kw">as </span><span class="prelude-ty">Option</span>&lt;bool&gt;, <span class="kw-2">&amp;</span>[
<span class="prelude-val">Some</span>(<span class="bool-val">true</span>),
<span class="prelude-val">None</span>,
<span class="prelude-val">Some</span>(<span class="bool-val">false</span>),
<span class="prelude-val">None</span>,
<span class="prelude-val">Some</span>(<span class="bool-val">false</span>),
]);
test_samples(<span class="kw-2">&amp;</span>Standard, Wrapping(<span class="number">0i32</span>), <span class="kw-2">&amp;</span>[
Wrapping(-<span class="number">2074640887</span>),
Wrapping(-<span class="number">1719949321</span>),
Wrapping(<span class="number">2018088303</span>),
Wrapping(-<span class="number">547181756</span>),
Wrapping(<span class="number">838957336</span>),
]);
<span class="comment">// We test only sub-sets of tuple and array impls
</span>test_samples(<span class="kw-2">&amp;</span>Standard, (), <span class="kw-2">&amp;</span>[(), (), (), (), ()]);
test_samples(<span class="kw-2">&amp;</span>Standard, (<span class="bool-val">false</span>,), <span class="kw-2">&amp;</span>[
(<span class="bool-val">true</span>,),
(<span class="bool-val">true</span>,),
(<span class="bool-val">false</span>,),
(<span class="bool-val">true</span>,),
(<span class="bool-val">false</span>,),
]);
test_samples(<span class="kw-2">&amp;</span>Standard, (<span class="bool-val">false</span>, <span class="bool-val">false</span>), <span class="kw-2">&amp;</span>[
(<span class="bool-val">true</span>, <span class="bool-val">true</span>),
(<span class="bool-val">false</span>, <span class="bool-val">true</span>),
(<span class="bool-val">false</span>, <span class="bool-val">false</span>),
(<span class="bool-val">true</span>, <span class="bool-val">false</span>),
(<span class="bool-val">false</span>, <span class="bool-val">false</span>),
]);
test_samples(<span class="kw-2">&amp;</span>Standard, [<span class="number">0u8</span>; <span class="number">0</span>], <span class="kw-2">&amp;</span>[[], [], [], [], []]);
test_samples(<span class="kw-2">&amp;</span>Standard, [<span class="number">0u8</span>; <span class="number">3</span>], <span class="kw-2">&amp;</span>[
[<span class="number">9</span>, <span class="number">247</span>, <span class="number">111</span>],
[<span class="number">68</span>, <span class="number">24</span>, <span class="number">13</span>],
[<span class="number">174</span>, <span class="number">19</span>, <span class="number">194</span>],
[<span class="number">172</span>, <span class="number">69</span>, <span class="number">213</span>],
[<span class="number">149</span>, <span class="number">207</span>, <span class="number">29</span>],
]);
}
}
</code></pre></div>
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