move IMA ADPCM decoder into codec_support

[nihav.git] / nihav-codec-support / src / codecs / imaadpcm.rs

diff --git a/nihav-codec-support/src/codecs/imaadpcm.rs b/nihav-codec-support/src/codecs/imaadpcm.rs
new file mode 100644 (file)
index 0000000..6ff92eb
--- /dev/null
+++ b/nihav-codec-support/src/codecs/imaadpcm.rs
@@ -0,0 +1,60 @@
+//! IMA ADPCM decoding functionality.
+
+///! IMA ADPCM step change table.
+pub const IMA_STEPS: [i8; 16] = [
+    -1, -1, -1, -1, 2, 4, 6, 8,
+    -1, -1, -1, -1, 2, 4, 6, 8
+];
+
+///! IMA ADPCM step size table.
+pub const IMA_STEP_TABLE: [i32; 89] = [
+        7,     8,     9,    10,    11,    12,    13,    14,
+       16,    17,    19,    21,    23,    25,    28,    31,
+       34,    37,    41,    45,    50,    55,    60,    66,
+       73,    80,    88,    97,   107,   118,   130,   143,
+      157,   173,   190,   209,   230,   253,   279,   307,
+      337,   371,   408,   449,   494,   544,   598,   658,
+      724,   796,   876,   963,  1060,  1166,  1282,  1411,
+     1552,  1707,  1878,  2066,  2272,  2499,  2749,  3024,
+     3327,  3660,  4026,  4428,  4871,  5358,  5894,  6484,
+     7132,  7845,  8630,  9493, 10442, 11487, 12635, 13899,
+    15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767
+];
+
+///! Maximum step value for IMA ADPCM.
+pub const IMA_MAX_STEP: u8 = 88;
+
+///! Decoder for IMA ADPCM.
+pub struct IMAState {
+    ///! Current sample value.
+    pub predictor:  i32,
+    ///! Current step index.
+    pub step:       usize,
+}
+
+impl IMAState {
+    ///! Constructs a new instance of `IMAState`.
+    pub fn new() -> Self {
+        Self {
+            predictor:  0,
+            step:       0,
+        }
+    }
+    ///! Re-initialises decoder with new predictor and step values.
+    pub fn reset(&mut self, predictor: i16, step: u8) {
+        self.predictor  = i32::from(predictor);
+        self.step       = step.min(IMA_MAX_STEP) as usize;
+    }
+    ///! Computes a new sample value from an input nibble.
+    pub fn expand_sample(&mut self, nibble: u8) -> i16 {
+        let istep = (self.step as isize) + (IMA_STEPS[(nibble & 0xF) as usize] as isize);
+        let sign = (nibble & 8) != 0;
+        let diff = (i32::from(2 * (nibble & 7) + 1) * IMA_STEP_TABLE[self.step]) >> 3;
+        let sample = if !sign { self.predictor + diff } else { self.predictor - diff };
+        self.predictor = sample.max(i32::from(std::i16::MIN)).min(i32::from(std::i16::MAX));
+        self.step = istep.max(0).min(IMA_MAX_STEP as isize) as usize;
+        self.predictor as i16
+    }
+}
+
+