From 17f3c6cc6c68d91fee29b1ec821609808ef2338f Mon Sep 17 00:00:00 2001
From: Robbert van der Helm <mail@robbertvanderhelm.nl>
Date: Mon, 7 Mar 2022 20:52:37 +0100
Subject: [PATCH] Add an in-place version of the Hann function

---
 src/util/window.rs | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/util/window.rs b/src/util/window.rs
index 0d8b60de..12423024 100644
--- a/src/util/window.rs
+++ b/src/util/window.rs
@@ -17,6 +17,18 @@ pub fn hann(size: usize) -> Vec<f32> {
         .collect()
 }
 
+/// The same as [`hann()`], but filling an existing slice instead.
+pub fn hann_in_place(window: &mut [f32]) {
+    let size = window.len();
+
+    // We want to scale `[0, size - 1]` to `[0, pi]`.
+    let scale = (size as f32 - 1.0).recip() * f32::consts::TAU;
+    for (i, sample) in window.iter_mut().enumerate() {
+        let cos = (i as f32 * scale).cos();
+        *sample = 0.5 - (0.5 * cos)
+    }
+}
+
 /// Multiply a buffer with a window function.
 #[inline]
 pub fn multiply_with_window(buffer: &mut [f32], window_function: &[f32]) {