split nihav-codec-support crate from nihav-core

The former is intended just for NihAV decoders, the latter is for both
NihAV crates and for the code using NihAV.

1 files changed, 59 insertions, 0 deletions

diff --git a/nihav-codec-support/src/dsp/window.rs b/nihav-codec-support/src/dsp/window.rs
new file mode 100644
index 0000000..eb350e3
--- /dev/null
+++ b/nihav-codec-support/src/dsp/window.rs
@@ -0,0 +1,59 @@
+//! Window generating functions.
+use std::f32::consts;
+
+/// Known window types.
+#[derive(Debug,Clone,Copy,PartialEq)]
+pub enum WindowType {
+    /// Simple square window.
+    Square,
+    /// Simple sine window.
+    Sine,
+    /// Kaiser-Bessel derived window.
+    KaiserBessel(f32),
+}
+
+/// Calculates window coefficients for the requested window type and size.
+///
+/// Set `half` flag to calculate only the first half of the window.
+pub fn generate_window(mode: WindowType, scale: f32, size: usize, half: bool, dst: &mut [f32]) {
+    match mode {
+        WindowType::Square => {
+                for n in 0..size { dst[n] = scale; }
+            },
+        WindowType::Sine => {
+                let param = if half {
+                        consts::PI / ((2 * size) as f32)
+                    } else {
+                        consts::PI / (size as f32)
+                    };
+                for n in 0..size {
+                    dst[n] = (((n as f32) + 0.5) * param).sin() * scale;
+                }
+            },
+        WindowType::KaiserBessel(alpha) => {
+                let dlen = if half { size as f32 } else { (size as f32) * 0.5 };
+                let alpha2 = f64::from((alpha * consts::PI / dlen) * (alpha * consts::PI / dlen));
+
+                let mut kb: Vec<f64> = Vec::with_capacity(size);
+                let mut sum = 0.0;
+                for n in 0..size {
+                    let b = bessel_i0(((n * (size - n)) as f64) * alpha2);
+                    sum += b;
+                    kb.push(sum);
+                }
+                sum += 1.0;
+                for n in 0..size {
+                    dst[n] = (kb[n] / sum).sqrt() as f32;
+                }
+            },
+    };
+}
+
+fn bessel_i0(inval: f64) -> f64 {
+    let mut val: f64 = 1.0;
+    for n in (1..64).rev() {
+        val *= inval / f64::from(n * n);
+        val += 1.0;
+    }
+    val
+}