implemented some crossfade curves

src/dsp/helpers.rs

@@ -249,11 +249,54 @@ impl SplitMix64 {
     }
 }
 
+/// Linear crossfade.
+///
+/// * `v1` - signal 1, range -1.0 to 1.0
+/// * `v2` - signal 2, range -1.0 to 1.0
+/// * `mix` - mix position, range 0.0 to 1.0, mid is at 0.5
 #[inline]
 pub fn crossfade(v1: f32, v2: f32, mix: f32) -> f32 {
     v1 * (1.0 - mix) + v2 * mix
 }
 
+/// Constant power crossfade.
+///
+/// * `v1` - signal 1, range -1.0 to 1.0
+/// * `v2` - signal 2, range -1.0 to 1.0
+/// * `mix` - mix position, range 0.0 to 1.0, mid is at 0.5
+#[inline]
+pub fn crossfade_cpow(v1: f32, v2: f32, mix: f32) -> f32 {
+    let s1 = (mix * std::f32::consts::FRAC_PI_2).sin();
+    let s2 = ((1.0 - mix) * std::f32::consts::FRAC_PI_2).sin();
+    v1 * s2 + v2 * s1
+}
+
+const CROSS_LOG_MIN : f32 = -13.815510557964274; // (0.000001_f32).ln();
+const CROSS_LOG_MAX : f32 = 0.0;                 // (1.0_f32).ln();
+
+/// Logarithmic crossfade.
+///
+/// * `v1` - signal 1, range -1.0 to 1.0
+/// * `v2` - signal 2, range -1.0 to 1.0
+/// * `mix` - mix position, range 0.0 to 1.0, mid is at 0.5
+#[inline]
+pub fn crossfade_log(v1: f32, v2: f32, mix: f32) -> f32 {
+    let x =
+        (mix * (CROSS_LOG_MAX - CROSS_LOG_MIN) + CROSS_LOG_MIN)
+        .exp();
+    crossfade(v1, v2, x)
+}
+
+/// Exponential crossfade.
+///
+/// * `v1` - signal 1, range -1.0 to 1.0
+/// * `v2` - signal 2, range -1.0 to 1.0
+/// * `mix` - mix position, range 0.0 to 1.0, mid is at 0.5
+#[inline]
+pub fn crossfade_exp(v1: f32, v2: f32, mix: f32) -> f32 {
+    crossfade(v1, v2, mix * mix)
+}
+
 #[inline]
 pub fn clamp(f: f32, min: f32, max: f32) -> f32 {
          if f < min { min }