Added a Rust port of Leonhard Grünschloß's Sobol sampler.

The Halton sampler appears to be better, but it was fun to add
this anyway!

Cargo.lock

@@ -151,6 +151,7 @@ dependencies = [
  "rustc-serialize 0.3.23 (registry+https://github.com/rust-lang/crates.io-index)",
  "scoped_threadpool 0.1.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "simd 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sobol 0.1.0",
  "spectra_xyz 0.1.0",
  "time 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -180,6 +181,10 @@ name = "simd"
 version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "sobol"
+version = "0.1.0"
+
 [[package]]
 name = "strsim"
 version = "0.6.0"

Cargo.toml

@@ -1,5 +1,10 @@
 [workspace]
-members = ["sub_crates/mem_arena", "sub_crates/halton", "sub_crates/spectra_xyz"]
+members = [
+    "sub_crates/mem_arena",
+    "sub_crates/halton",
+    "sub_crates/sobol",
+    "sub_crates/spectra_xyz"
+]
 
 [package]
 name = "psychopath"
@@ -35,5 +40,8 @@ path = "sub_crates/halton"
 [dependencies.mem_arena]
 path = "sub_crates/mem_arena"
 
+[dependencies.sobol]
+path = "sub_crates/sobol"
+
 [dependencies.spectra_xyz]
 path = "sub_crates/spectra_xyz"

sub_crates/halton/build.rs

@@ -29,7 +29,7 @@ use std::path::Path;
 
 
 /// How many components to generate.
-const NUM_DIMENSIONS: usize = 128;
+const NUM_DIMENSIONS: usize = 256;
 
 fn main() {
     let out_dir = env::var("OUT_DIR").unwrap();

sub_crates/sobol/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "sobol"
+version = "0.1.0"
+authors = ["Nathan Vegdahl <cessen@cessen.com>"]
+license = "MIT"
+
+[lib]
+name = "sobol"
+path = "src/lib.rs"

sub_crates/sobol/src/lib.rs

@@ -0,0 +1,54 @@
+// Copyright (c) 2012 Leonhard Gruenschloss (leonhard@gruenschloss.org)
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights to
+// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+// of the Software, and to permit persons to whom the Software is furnished to do
+// so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// Adapted to Rust by Nathan Vegdahl (2017)
+
+mod matrices;
+
+pub use matrices::NUM_DIMENSIONS;
+use matrices::{SIZE, MATRICES};
+
+/// Compute one component of the Sobol'-sequence, where the component
+/// corresponds to the dimension parameter, and the index specifies
+/// the point inside the sequence. The scramble parameter can be used
+/// to permute elementary intervals, and might be chosen randomly to
+/// generate a randomized QMC sequence.
+#[inline]
+pub fn sample_with_scramble(dimension: u32, mut index: u32, scramble: u32) -> f32 {
+    assert!((dimension as usize) < NUM_DIMENSIONS);
+
+    let mut result = scramble;
+    let mut i = (dimension as usize) * SIZE;
+    while index != 0 {
+        if (index & 1) != 0 {
+            result ^= MATRICES[i];
+        }
+
+        index >>= 1;
+        i += 1;
+    }
+
+    return result as f32 * (1.0 / (1u64 << 32) as f32);
+}
+
+#[inline]
+pub fn sample(dimension: u32, index: u32) -> f32 {
+    sample_with_scramble(dimension, index, 0)
+}