From 02532148107b3ec8b05a114ef95335b03bd73b9c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Robert=20J=C3=B6rdens?= <rj@quartiq.de>
Date: Tue, 22 Jun 2021 22:53:51 +0200
Subject: [PATCH] lowpass: make it work for k=0

---
 dsp/src/lowpass.rs | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/dsp/src/lowpass.rs b/dsp/src/lowpass.rs
index 265929b..7573e28 100644
--- a/dsp/src/lowpass.rs
+++ b/dsp/src/lowpass.rs
@@ -25,7 +25,6 @@ impl<const N: usize> Lowpass<N> {
     /// Filtered output y.
     pub fn update(&mut self, x: i32, k: u8) -> i32 {
         debug_assert!(k & 31 == k);
-        debug_assert!((k - 1) & 31 == k - 1);
         // This is an unrolled and optimized first-order IIR loop
         // that works for all possible time constants.
         // Note T-DF-I and the zeros at Nyquist.
@@ -35,6 +34,6 @@ impl<const N: usize> Lowpass<N> {
             *y += dy;
             x = *y - (dy >> 1);
         }
-        x.saturating_add((self.y.len() as i32) << (k - 1))
+        x.saturating_add((self.y.len() as i32) << (k - 1).max(0))
     }
 }