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//! 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;
#[derive(Clone,Copy,Debug)]
///! 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
}
}
impl Default for IMAState {
fn default() -> Self {
Self::new()
}
}
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