feat: add dsp module for signal generation

examples/dsp/mod.rs

@@ -0,0 +1,2 @@
+pub mod osc;
+pub mod wavetable;

examples/dsp/osc.rs

@@ -0,0 +1,69 @@
+#![allow(dead_code)]
+#[allow(unused_imports)]
+use super::wavetable;
+
+// - wavetable oscillator -----------------------------------------------------
+
+pub struct Wavetable {
+    pub dx: f32, // frequency * (1 / fs)
+    phasor: f32,
+    shape: Shape,
+}
+
+pub enum Shape {
+    Sin,
+    Saw,
+}
+
+impl Wavetable {
+    pub const fn new(shape: Shape) -> Wavetable {
+        Wavetable {
+            shape: shape,
+            dx: 0.004_988_662_f32, // 220Hz @ fs=44100KHz
+            phasor: 0.,
+        }
+    }
+
+    pub fn step(&mut self) -> f32 {
+        let wt = match self.shape {
+            Shape::Saw => &wavetable::SAW,
+            Shape::Sin => &wavetable::SIN,
+        };
+
+        let wt_index = self.phasor * wavetable::LENGTH as f32;
+        let signal = wt[wt_index as usize];
+        self.phasor += self.dx;
+        if self.phasor >= 1.0_f32 {
+            self.phasor -= 1.0_f32;
+        }
+        signal
+    }
+
+    pub fn block(&mut self, buffer: &mut [f32; crate::BLOCK_LENGTH]) {
+        let wt = match self.shape {
+            Shape::Saw => &wavetable::SAW,
+            Shape::Sin => &wavetable::SIN,
+        };
+
+        let length = buffer.len();
+        let mut index = 0;
+        while index < length {
+            let wt_index = self.phasor * wavetable::LENGTH as f32;
+            let signal: f32 = wt[wt_index as usize];
+
+            buffer[index] = signal;
+            self.phasor += self.dx;
+            if self.phasor >= 1.0_f32 {
+                self.phasor -= 1.0_f32;
+            }
+            index += 1;
+        }
+    }
+
+    pub fn block2(&mut self, block: &mut [(f32, f32); crate::BLOCK_LENGTH]) {
+        for frame in block {
+            let sample = self.step();
+            *frame = (sample, sample);
+        }
+    }
+}