| 1 | //! IMA ADPCM decoding functionality. |
| 2 | |
| 3 | ///! IMA ADPCM step change table. |
| 4 | pub const IMA_STEPS: [i8; 16] = [ |
| 5 | -1, -1, -1, -1, 2, 4, 6, 8, |
| 6 | -1, -1, -1, -1, 2, 4, 6, 8 |
| 7 | ]; |
| 8 | |
| 9 | ///! IMA ADPCM step size table. |
| 10 | pub const IMA_STEP_TABLE: [i32; 89] = [ |
| 11 | 7, 8, 9, 10, 11, 12, 13, 14, |
| 12 | 16, 17, 19, 21, 23, 25, 28, 31, |
| 13 | 34, 37, 41, 45, 50, 55, 60, 66, |
| 14 | 73, 80, 88, 97, 107, 118, 130, 143, |
| 15 | 157, 173, 190, 209, 230, 253, 279, 307, |
| 16 | 337, 371, 408, 449, 494, 544, 598, 658, |
| 17 | 724, 796, 876, 963, 1060, 1166, 1282, 1411, |
| 18 | 1552, 1707, 1878, 2066, 2272, 2499, 2749, 3024, |
| 19 | 3327, 3660, 4026, 4428, 4871, 5358, 5894, 6484, |
| 20 | 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899, |
| 21 | 15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767 |
| 22 | ]; |
| 23 | |
| 24 | ///! Maximum step value for IMA ADPCM. |
| 25 | pub const IMA_MAX_STEP: u8 = 88; |
| 26 | |
| 27 | ///! Decoder for IMA ADPCM. |
| 28 | pub struct IMAState { |
| 29 | ///! Current sample value. |
| 30 | pub predictor: i32, |
| 31 | ///! Current step index. |
| 32 | pub step: usize, |
| 33 | } |
| 34 | |
| 35 | impl IMAState { |
| 36 | ///! Constructs a new instance of `IMAState`. |
| 37 | pub fn new() -> Self { |
| 38 | Self { |
| 39 | predictor: 0, |
| 40 | step: 0, |
| 41 | } |
| 42 | } |
| 43 | ///! Re-initialises decoder with new predictor and step values. |
| 44 | pub fn reset(&mut self, predictor: i16, step: u8) { |
| 45 | self.predictor = i32::from(predictor); |
| 46 | self.step = step.min(IMA_MAX_STEP) as usize; |
| 47 | } |
| 48 | ///! Computes a new sample value from an input nibble. |
| 49 | pub fn expand_sample(&mut self, nibble: u8) -> i16 { |
| 50 | let istep = (self.step as isize) + (IMA_STEPS[(nibble & 0xF) as usize] as isize); |
| 51 | let sign = (nibble & 8) != 0; |
| 52 | let diff = (i32::from(2 * (nibble & 7) + 1) * IMA_STEP_TABLE[self.step]) >> 3; |
| 53 | let sample = if !sign { self.predictor + diff } else { self.predictor - diff }; |
| 54 | self.predictor = sample.max(i32::from(std::i16::MIN)).min(i32::from(std::i16::MAX)); |
| 55 | self.step = istep.max(0).min(IMA_MAX_STEP as isize) as usize; |
| 56 | self.predictor as i16 |
| 57 | } |
| 58 | } |
| 59 | |
| 60 | impl Default for IMAState { |
| 61 | fn default() -> Self { |
| 62 | Self::new() |
| 63 | } |
| 64 | } |