From 5703db0b80eba55b9d24662b4c3bf5c56c52f737 Mon Sep 17 00:00:00 2001
From: NetterSilver <133535268+Silvertree2010@users.noreply.github.com>
Date: Tue, 20 Oct 2026 17:24:47 +0200
Subject: [PATCH] Fix normalize producing inf samples for subnormal peaks

Found while testing crates/dsp/src/offline.rs:62-79

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
---
 crates/dsp/src/offline.rs             | 18 ++++++++++++++----
 crates/dsp/tests/offline_normalize.rs | 19 +++++++++++++++++++
 2 files changed, 33 insertions(+), 4 deletions(-)
 create mode 100644 crates/dsp/tests/offline_normalize.rs

diff --git a/crates/dsp/src/offline.rs b/crates/dsp/src/offline.rs
index 8bbc80a6..337f3589 100644
--- a/crates/dsp/src/offline.rs
+++ b/crates/dsp/src/offline.rs
@@ -65,19 +65,29 @@ pub fn normalize(ch: &mut [Vec<f32>], target_db: f32, per_channel: bool) {
         for c in ch.iter_mut() {
             let p = peak(std::slice::from_ref(c));
             if p > 0.0 {
-                let g = target / p;
-                c.iter_mut().for_each(|s| *s *= g);
+                scale_to(c.iter_mut(), target, p);
             }
         }
     } else {
         let p = peak(ch);
         if p > 0.0 {
-            let g = target / p;
-            ch.iter_mut().flatten().for_each(|s| *s *= g);
+            scale_to(ch.iter_mut().flatten(), target, p);
         }
     }
 }
 
+/// Scales samples whose peak is `p` to `target`. A subnormal `p` makes the f32 gain overflow to
+/// infinity, so that case scales in f64.
+fn scale_to<'a>(samples: impl Iterator<Item = &'a mut f32>, target: f32, p: f32) {
+    let g = target / p;
+    if g.is_finite() {
+        samples.for_each(|s| *s *= g);
+    } else {
+        let g = f64::from(target) / f64::from(p);
+        samples.for_each(|s| *s = (f64::from(*s) * g) as f32);
+    }
+}
+
 /// Applies a gain change in dB.
 pub fn gain(ch: &mut [Vec<f32>], db: f32) {
     let g = db_to_gain(if db.is_nan() { 0.0 } else { db.min(96.0) });
diff --git a/crates/dsp/tests/offline_normalize.rs b/crates/dsp/tests/offline_normalize.rs
new file mode 100644
index 00000000..6ed47973
--- /dev/null
+++ b/crates/dsp/tests/offline_normalize.rs
@@ -0,0 +1,19 @@
+use soundcraft_dsp::offline::{normalize, peak};
+
+#[test]
+fn normalize_subnormal_peak_stays_finite() {
+    for per_channel in [false, true] {
+        let mut c = vec![vec![1e-44f32, -1e-44]];
+        normalize(&mut c, 0.0, per_channel);
+        assert!(c[0].iter().all(|s| s.is_finite()), "{c:?}");
+        assert!((peak(&c) - 1.0).abs() < 1e-3, "{c:?}");
+    }
+}
+
+#[test]
+fn normalize_silent_and_normal_channels() {
+    let mut c = vec![vec![0.0f32; 4], vec![0.25, -0.5]];
+    normalize(&mut c, 0.0, true);
+    assert_eq!(c[0], vec![0.0; 4]);
+    assert!((peak(&c[1..]) - 1.0).abs() < 1e-5);
+}