From fc9419e580c78dec63c668613bb1c56359468567 Mon Sep 17 00:00:00 2001
From: Matt McPherrin <git@mcpherrin.ca>
Date: Wed, 15 Jul 2015 15:27:15 -0700
Subject: [PATCH] A basic implementation, mostly untested!
---
src/lib.rs | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 65 insertions(+), 1 deletion(-)
diff --git a/src/lib.rs b/src/lib.rs
index a93251b..bfe3258 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,67 @@
+// This (implicitly/naively) uses a rectangular window. Some way to set up a window function
+// will be needed probably -- if mutating your samples before calling this isn't sufficient.
+
+/// Set up parameters (and some precomputed values for those).
+#[derive(Clone, Copy)]
+pub struct Parameters {
+ // Parameters we're working with
+ window_size: u32,
+ // Precomputed value:
+ sine: f32,
+ cosine: f32,
+ term_coefficient: f32,
+}
+
+pub struct Partial {
+ params: Parameters,
+ //count: u32,
+ prev: f32,
+ prevprev: f32,
+}
+
+impl Parameters {
+ pub fn new(target_freq: f32, sample_rate: f32, window_size: u32) -> Self {
+ use std::f32;
+ let k = target_freq * (window_size as f32) / sample_rate;
+ let omega = (f32::consts::PI * 2. * k) / (window_size as f32);
+ let cosine = omega.cos();
+ Parameters {
+ window_size: window_size,
+ sine: omega.sin(),
+ cosine: cosine,
+ term_coefficient: 2. * cosine,
+ }
+ }
+
+ pub fn start(self) -> Partial {
+ Partial{ params: self, prev: 0., prevprev: 0. }
+ }
+}
+
+impl Partial {
+ pub fn add(mut self, samples: &[u16]) -> Self {
+ for &sample in samples {
+ let this = self.params.term_coefficient * self.prev - self.prevprev + (sample as f32);
+ self.prevprev = self.prev;
+ self.prev = this;
+ }
+ self
+ }
+ pub fn finish(self) -> (f32, f32) {
+ let real = self.prev - self.prevprev * self.params.cosine;
+ let imag = self.prevprev * self.params.sine;
+ (real, imag)
+ }
+
+ pub fn finish_mag(self) -> f32 {
+ let (real, imag) = self.finish();
+ (real*real + imag*imag).sqrt()
+ }
+}
+
#[test]
-fn it_works() {
+fn zero_data() {
+ let p = Parameters::new(1800., 44100., 256);
+ assert!(p.start().add(&[0; 256]).finish_mag() == 0.);
+ assert!(p.start().add(&[0; 128]).add(&[0;128]).finish_mag() == 0.);
}
--
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