| 1 | use std::f32::consts; |
| 2 | use super::fft::*; |
| 3 | |
| 4 | pub struct IMDCT { |
| 5 | twiddle: Vec<FFTComplex>, |
| 6 | fft: FFT, |
| 7 | size: usize, |
| 8 | z: Vec<FFTComplex>, |
| 9 | } |
| 10 | |
| 11 | /* |
| 12 | fn imdct(src: &[f32], dst: &mut [f32], length: usize) { |
| 13 | for n in 0..length*2 { |
| 14 | dst[n] = 0.0; |
| 15 | for k in 0..length { |
| 16 | dst[n] += src[k] * (consts::PI / (length as f32) * ((n as f32) + 0.5 + ((length/2) as f32)) * ((k as f32) + 0.5)).cos(); |
| 17 | } |
| 18 | } |
| 19 | }*/ |
| 20 | |
| 21 | impl IMDCT { |
| 22 | pub fn new(size: usize, scaledown: bool) -> Self { |
| 23 | let mut twiddle: Vec<FFTComplex> = Vec::with_capacity(size / 4); |
| 24 | let factor = 2.0 * consts::PI / ((8 * size) as f32); |
| 25 | let scale = if scaledown { (1.0 / (size as f32)).sqrt() } else { 1.0 }; |
| 26 | for k in 0..size/4 { |
| 27 | twiddle.push(FFTComplex::exp(factor * ((8 * k + 1) as f32)).scale(scale)); |
| 28 | } |
| 29 | let fft = FFTBuilder::new_fft(size/4, false); |
| 30 | let mut z: Vec<FFTComplex> = Vec::with_capacity(size / 2); |
| 31 | z.resize(size / 2, FFTC_ZERO); |
| 32 | IMDCT { twiddle, fft, size, z } |
| 33 | } |
| 34 | pub fn imdct(&mut self, src: &[f32], dst: &mut [f32]) { |
| 35 | let size2 = self.size / 2; |
| 36 | let size4 = self.size / 4; |
| 37 | let size8 = self.size / 8; |
| 38 | for k in 0..size4 { |
| 39 | let c = FFTComplex { re: src[size2 - 2 * k - 1], im: src[ 2 * k] }; |
| 40 | self.z[k] = c * self.twiddle[k]; |
| 41 | } |
| 42 | self.fft.do_ifft_inplace(&mut self.z); |
| 43 | for k in 0..size4 { |
| 44 | self.z[k] *= self.twiddle[k]; |
| 45 | } |
| 46 | for n in 0..size8 { |
| 47 | dst[ 2 * n] = -self.z[size8 + n] .im; |
| 48 | dst[ 2 * n + 1] = self.z[size8 - n - 1].re; |
| 49 | dst[ size4 + 2 * n] = -self.z[ n] .re; |
| 50 | dst[ size4 + 2 * n + 1] = self.z[size4 - n - 1].im; |
| 51 | dst[ size2 + 2 * n] = -self.z[size8 + n] .re; |
| 52 | dst[ size2 + 2 * n + 1] = self.z[size8 - n - 1].im; |
| 53 | dst[3 * size4 + 2 * n] = self.z[ n] .im; |
| 54 | dst[3 * size4 + 2 * n + 1] = -self.z[size4 - n - 1].re; |
| 55 | } |
| 56 | } |
| 57 | } |