Add a decibel to gain conversion function

nih_plug/src/lib.rs

@@ -17,3 +17,4 @@
 pub mod debug;
 pub mod params;
 pub mod plugin;
+pub mod util;

nih_plug/src/util.rs

@@ -0,0 +1,46 @@
+// nih-plug: plugins, but rewritten in Rust
+// Copyright (C) 2022 Robbert van der Helm
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+pub const MINUS_INFINITY_DB: f32 = -100.0;
+
+/// Convert decibels to gain, treating anything below -100 dB as minus infinity.
+pub fn db_to_gain(dbs: f32) -> f32 {
+    if dbs > MINUS_INFINITY_DB {
+        10.0f32.powf(dbs * 0.05)
+    } else {
+        0.0
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_db_to_gain_positive() {
+        assert_eq!(db_to_gain(3.0), 1.4125376);
+    }
+
+    #[test]
+    fn test_db_to_gain_negative() {
+        assert_eq!(db_to_gain(-3.0), 1.4125376f32.recip());
+    }
+
+    #[test]
+    fn test_db_to_gain_minus_infinity() {
+        assert_eq!(db_to_gain(-100.0), 0.0);
+    }
+}