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| </pre><pre class="rust"><code><span class="comment">// Copyright 2018-2021 Developers of the Rand project.</span> |
| <span class="comment">// Copyright 2017 Paul Dicker.</span> |
| <span class="comment">// Copyright 2014-2017, 2019 Melissa O'Neill and PCG Project contributors</span> |
| <span class="comment">//</span> |
| <span class="comment">// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or</span> |
| <span class="comment">// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license</span> |
| <span class="comment">// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your</span> |
| <span class="comment">// option. This file may not be copied, modified, or distributed</span> |
| <span class="comment">// except according to those terms.</span> |
| |
| <span class="doccomment">//! PCG random number generators</span> |
| |
| <span class="comment">// This is the cheap multiplier used by PCG for 128-bit state.</span> |
| <span class="kw">const</span> <span class="ident">MULTIPLIER</span>: <span class="ident">u64</span> <span class="op">=</span> <span class="number">15750249268501108917</span>; |
| |
| <span class="kw">use</span> <span class="ident">core::fmt</span>; |
| <span class="kw">use</span> <span class="ident">rand_core</span>::{<span class="ident">impls</span>, <span class="ident">le</span>, <span class="ident">Error</span>, <span class="ident">RngCore</span>, <span class="ident">SeedableRng</span>}; |
| <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"serde1"</span>)]</span> <span class="kw">use</span> <span class="ident">serde</span>::{<span class="ident">Deserialize</span>, <span class="ident">Serialize</span>}; |
| |
| <span class="doccomment">/// A PCG random number generator (CM DXSM 128/64 (LCG) variant).</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// Permuted Congruential Generator with 128-bit state, internal Linear</span> |
| <span class="doccomment">/// Congruential Generator, and 64-bit output via "double xorshift multiply"</span> |
| <span class="doccomment">/// output function.</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// This is a 128-bit LCG with explicitly chosen stream with the PCG-DXSM</span> |
| <span class="doccomment">/// output function. This corresponds to `pcg_engines::cm_setseq_dxsm_128_64`</span> |
| <span class="doccomment">/// from pcg_cpp and `PCG64DXSM` from NumPy.</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// Despite the name, this implementation uses 32 bytes (256 bit) space</span> |
| <span class="doccomment">/// comprising 128 bits of state and 128 bits stream selector. These are both</span> |
| <span class="doccomment">/// set by `SeedableRng`, using a 256-bit seed.</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// Note that while two generators with different stream parameter may be</span> |
| <span class="doccomment">/// closely correlated, this is [mitigated][upgrading-pcg64] by the DXSM output function.</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// [upgrading-pcg64]: https://numpy.org/doc/stable/reference/random/upgrading-pcg64.html</span> |
| <span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>)]</span> |
| <span class="attribute">#[<span class="ident">cfg_attr</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"serde1"</span>, <span class="ident">derive</span>(<span class="ident">Serialize</span>, <span class="ident">Deserialize</span>))]</span> |
| <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Lcg128CmDxsm64</span> { |
| <span class="ident">state</span>: <span class="ident">u128</span>, |
| <span class="ident">increment</span>: <span class="ident">u128</span>, |
| } |
| |
| <span class="doccomment">/// [`Lcg128CmDxsm64`] is also known as `PCG64DXSM`.</span> |
| <span class="kw">pub</span> <span class="kw">type</span> <span class="ident">Pcg64Dxsm</span> <span class="op">=</span> <span class="ident">Lcg128CmDxsm64</span>; |
| |
| <span class="kw">impl</span> <span class="ident">Lcg128CmDxsm64</span> { |
| <span class="doccomment">/// Multi-step advance functions (jump-ahead, jump-back)</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// The method used here is based on Brown, "Random Number Generation</span> |
| <span class="doccomment">/// with Arbitrary Stride,", Transactions of the American Nuclear</span> |
| <span class="doccomment">/// Society (Nov. 1994). The algorithm is very similar to fast</span> |
| <span class="doccomment">/// exponentiation.</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// Even though delta is an unsigned integer, we can pass a</span> |
| <span class="doccomment">/// signed integer to go backwards, it just goes "the long way round".</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// Using this function is equivalent to calling `next_64()` `delta`</span> |
| <span class="doccomment">/// number of times.</span> |
| <span class="attribute">#[<span class="ident">inline</span>]</span> |
| <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">advance</span>(<span class="kw-2">&mut</span> <span class="self">self</span>, <span class="ident">delta</span>: <span class="ident">u128</span>) { |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">acc_mult</span>: <span class="ident">u128</span> <span class="op">=</span> <span class="number">1</span>; |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">acc_plus</span>: <span class="ident">u128</span> <span class="op">=</span> <span class="number">0</span>; |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_mult</span> <span class="op">=</span> <span class="ident">MULTIPLIER</span> <span class="kw">as</span> <span class="ident">u128</span>; |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur_plus</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">increment</span>; |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">mdelta</span> <span class="op">=</span> <span class="ident">delta</span>; |
| |
| <span class="kw">while</span> <span class="ident">mdelta</span> <span class="op">></span> <span class="number">0</span> { |
| <span class="kw">if</span> (<span class="ident">mdelta</span> <span class="op">&</span> <span class="number">1</span>) <span class="op">!</span><span class="op">=</span> <span class="number">0</span> { |
| <span class="ident">acc_mult</span> <span class="op">=</span> <span class="ident">acc_mult</span>.<span class="ident">wrapping_mul</span>(<span class="ident">cur_mult</span>); |
| <span class="ident">acc_plus</span> <span class="op">=</span> <span class="ident">acc_plus</span>.<span class="ident">wrapping_mul</span>(<span class="ident">cur_mult</span>).<span class="ident">wrapping_add</span>(<span class="ident">cur_plus</span>); |
| } |
| <span class="ident">cur_plus</span> <span class="op">=</span> <span class="ident">cur_mult</span>.<span class="ident">wrapping_add</span>(<span class="number">1</span>).<span class="ident">wrapping_mul</span>(<span class="ident">cur_plus</span>); |
| <span class="ident">cur_mult</span> <span class="op">=</span> <span class="ident">cur_mult</span>.<span class="ident">wrapping_mul</span>(<span class="ident">cur_mult</span>); |
| <span class="ident">mdelta</span> <span class="op">/</span><span class="op">=</span> <span class="number">2</span>; |
| } |
| <span class="self">self</span>.<span class="ident">state</span> <span class="op">=</span> <span class="ident">acc_mult</span>.<span class="ident">wrapping_mul</span>(<span class="self">self</span>.<span class="ident">state</span>).<span class="ident">wrapping_add</span>(<span class="ident">acc_plus</span>); |
| } |
| |
| <span class="doccomment">/// Construct an instance compatible with PCG seed and stream.</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// Note that the highest bit of the `stream` parameter is discarded</span> |
| <span class="doccomment">/// to simplify upholding internal invariants.</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// Note that while two generators with different stream parameter may be</span> |
| <span class="doccomment">/// closely correlated, this is [mitigated][upgrading-pcg64] by the DXSM output function.</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// PCG specifies the following default values for both parameters:</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// - `state = 0xcafef00dd15ea5e5`</span> |
| <span class="doccomment">/// - `stream = 0xa02bdbf7bb3c0a7ac28fa16a64abf96`</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// [upgrading-pcg64]: https://numpy.org/doc/stable/reference/random/upgrading-pcg64.html</span> |
| <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">state</span>: <span class="ident">u128</span>, <span class="ident">stream</span>: <span class="ident">u128</span>) -> <span class="self">Self</span> { |
| <span class="comment">// The increment must be odd, hence we discard one bit:</span> |
| <span class="kw">let</span> <span class="ident">increment</span> <span class="op">=</span> (<span class="ident">stream</span> <span class="op"><</span><span class="op"><</span> <span class="number">1</span>) <span class="op">|</span> <span class="number">1</span>; |
| <span class="ident"><span class="self">Self</span>::from_state_incr</span>(<span class="ident">state</span>, <span class="ident">increment</span>) |
| } |
| |
| <span class="attribute">#[<span class="ident">inline</span>]</span> |
| <span class="kw">fn</span> <span class="ident">from_state_incr</span>(<span class="ident">state</span>: <span class="ident">u128</span>, <span class="ident">increment</span>: <span class="ident">u128</span>) -> <span class="self">Self</span> { |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">pcg</span> <span class="op">=</span> <span class="self">Self</span> { <span class="ident">state</span>, <span class="ident">increment</span> }; |
| <span class="comment">// Move away from initial value:</span> |
| <span class="ident">pcg</span>.<span class="ident">state</span> <span class="op">=</span> <span class="ident">pcg</span>.<span class="ident">state</span>.<span class="ident">wrapping_add</span>(<span class="ident">pcg</span>.<span class="ident">increment</span>); |
| <span class="ident">pcg</span>.<span class="ident">step</span>(); |
| <span class="ident">pcg</span> |
| } |
| |
| <span class="attribute">#[<span class="ident">inline</span>(<span class="ident">always</span>)]</span> |
| <span class="kw">fn</span> <span class="ident">step</span>(<span class="kw-2">&mut</span> <span class="self">self</span>) { |
| <span class="comment">// prepare the LCG for the next round</span> |
| <span class="self">self</span>.<span class="ident">state</span> <span class="op">=</span> <span class="self">self</span> |
| .<span class="ident">state</span> |
| .<span class="ident">wrapping_mul</span>(<span class="ident">MULTIPLIER</span> <span class="kw">as</span> <span class="ident">u128</span>) |
| .<span class="ident">wrapping_add</span>(<span class="self">self</span>.<span class="ident">increment</span>); |
| } |
| } |
| |
| <span class="comment">// Custom Debug implementation that does not expose the internal state</span> |
| <span class="kw">impl</span> <span class="ident">fmt::Debug</span> <span class="kw">for</span> <span class="ident">Lcg128CmDxsm64</span> { |
| <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&mut</span> <span class="ident">fmt::Formatter</span>) -> <span class="ident">fmt::Result</span> { |
| <span class="macro">write!</span>(<span class="ident">f</span>, <span class="string">"Lcg128CmDxsm64 {{}}"</span>) |
| } |
| } |
| |
| <span class="kw">impl</span> <span class="ident">SeedableRng</span> <span class="kw">for</span> <span class="ident">Lcg128CmDxsm64</span> { |
| <span class="kw">type</span> <span class="ident">Seed</span> <span class="op">=</span> [<span class="ident">u8</span>; <span class="number">32</span>]; |
| |
| <span class="doccomment">/// We use a single 255-bit seed to initialise the state and select a stream.</span> |
| <span class="doccomment">/// One `seed` bit (lowest bit of `seed[8]`) is ignored.</span> |
| <span class="kw">fn</span> <span class="ident">from_seed</span>(<span class="ident">seed</span>: <span class="ident"><span class="self">Self</span>::Seed</span>) -> <span class="self">Self</span> { |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">seed_u64</span> <span class="op">=</span> [<span class="number">0u64</span>; <span class="number">4</span>]; |
| <span class="ident">le::read_u64_into</span>(<span class="kw-2">&</span><span class="ident">seed</span>, <span class="kw-2">&mut</span> <span class="ident">seed_u64</span>); |
| <span class="kw">let</span> <span class="ident">state</span> <span class="op">=</span> <span class="ident">u128::from</span>(<span class="ident">seed_u64</span>[<span class="number">0</span>]) <span class="op">|</span> (<span class="ident">u128::from</span>(<span class="ident">seed_u64</span>[<span class="number">1</span>]) <span class="op"><</span><span class="op"><</span> <span class="number">64</span>); |
| <span class="kw">let</span> <span class="ident">incr</span> <span class="op">=</span> <span class="ident">u128::from</span>(<span class="ident">seed_u64</span>[<span class="number">2</span>]) <span class="op">|</span> (<span class="ident">u128::from</span>(<span class="ident">seed_u64</span>[<span class="number">3</span>]) <span class="op"><</span><span class="op"><</span> <span class="number">64</span>); |
| |
| <span class="comment">// The increment must be odd, hence we discard one bit:</span> |
| <span class="ident"><span class="self">Self</span>::from_state_incr</span>(<span class="ident">state</span>, <span class="ident">incr</span> <span class="op">|</span> <span class="number">1</span>) |
| } |
| } |
| |
| <span class="kw">impl</span> <span class="ident">RngCore</span> <span class="kw">for</span> <span class="ident">Lcg128CmDxsm64</span> { |
| <span class="attribute">#[<span class="ident">inline</span>]</span> |
| <span class="kw">fn</span> <span class="ident">next_u32</span>(<span class="kw-2">&mut</span> <span class="self">self</span>) -> <span class="ident">u32</span> { |
| <span class="self">self</span>.<span class="ident">next_u64</span>() <span class="kw">as</span> <span class="ident">u32</span> |
| } |
| |
| <span class="attribute">#[<span class="ident">inline</span>]</span> |
| <span class="kw">fn</span> <span class="ident">next_u64</span>(<span class="kw-2">&mut</span> <span class="self">self</span>) -> <span class="ident">u64</span> { |
| <span class="kw">let</span> <span class="ident">val</span> <span class="op">=</span> <span class="ident">output_dxsm</span>(<span class="self">self</span>.<span class="ident">state</span>); |
| <span class="self">self</span>.<span class="ident">step</span>(); |
| <span class="ident">val</span> |
| } |
| |
| <span class="attribute">#[<span class="ident">inline</span>]</span> |
| <span class="kw">fn</span> <span class="ident">fill_bytes</span>(<span class="kw-2">&mut</span> <span class="self">self</span>, <span class="ident">dest</span>: <span class="kw-2">&mut</span> [<span class="ident">u8</span>]) { |
| <span class="ident">impls::fill_bytes_via_next</span>(<span class="self">self</span>, <span class="ident">dest</span>) |
| } |
| |
| <span class="attribute">#[<span class="ident">inline</span>]</span> |
| <span class="kw">fn</span> <span class="ident">try_fill_bytes</span>(<span class="kw-2">&mut</span> <span class="self">self</span>, <span class="ident">dest</span>: <span class="kw-2">&mut</span> [<span class="ident">u8</span>]) -> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">Error</span><span class="op">></span> { |
| <span class="self">self</span>.<span class="ident">fill_bytes</span>(<span class="ident">dest</span>); |
| <span class="prelude-val">Ok</span>(()) |
| } |
| } |
| |
| <span class="attribute">#[<span class="ident">inline</span>(<span class="ident">always</span>)]</span> |
| <span class="kw">fn</span> <span class="ident">output_dxsm</span>(<span class="ident">state</span>: <span class="ident">u128</span>) -> <span class="ident">u64</span> { |
| <span class="comment">// See https://github.com/imneme/pcg-cpp/blob/ffd522e7188bef30a00c74dc7eb9de5faff90092/include/pcg_random.hpp#L1016</span> |
| <span class="comment">// for a short discussion of the construction and its original implementation.</span> |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">hi</span> <span class="op">=</span> (<span class="ident">state</span> <span class="op">></span><span class="op">></span> <span class="number">64</span>) <span class="kw">as</span> <span class="ident">u64</span>; |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">lo</span> <span class="op">=</span> <span class="ident">state</span> <span class="kw">as</span> <span class="ident">u64</span>; |
| |
| <span class="ident">lo</span> <span class="op">|</span><span class="op">=</span> <span class="number">1</span>; |
| <span class="ident">hi</span> <span class="op">^</span><span class="op">=</span> <span class="ident">hi</span> <span class="op">></span><span class="op">></span> <span class="number">32</span>; |
| <span class="ident">hi</span> <span class="op">=</span> <span class="ident">hi</span>.<span class="ident">wrapping_mul</span>(<span class="ident">MULTIPLIER</span>); |
| <span class="ident">hi</span> <span class="op">^</span><span class="op">=</span> <span class="ident">hi</span> <span class="op">></span><span class="op">></span> <span class="number">48</span>; |
| <span class="ident">hi</span> <span class="op">=</span> <span class="ident">hi</span>.<span class="ident">wrapping_mul</span>(<span class="ident">lo</span>); |
| |
| <span class="ident">hi</span> |
| } |
| </code></pre></div> |
| </section><section id="search" class="content hidden"></section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="rand_pcg" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.60.0-nightly (1bd4fdc94 2022-01-12)" ></div> |
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