pxdct 0.3.2

/*
 * // Copyright (c) Radzivon Bartoshyk 12/2025. All rights reserved.
 * //
 * // Redistribution and use in source and binary forms, with or without modification,
 * // are permitted provided that the following conditions are met:
 * //
 * // 1.  Redistributions of source code must retain the above copyright notice, this
 * // list of conditions and the following disclaimer.
 * //
 * // 2.  Redistributions in binary form must reproduce the above copyright notice,
 * // this list of conditions and the following disclaimer in the documentation
 * // and/or other materials provided with the distribution.
 * //
 * // 3.  Neither the name of the copyright holder nor the names of its
 * // contributors may be used to endorse or promote products derived from
 * // this software without specific prior written permission.
 * //
 * // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
use crate::bidirectional::BidirectionalStore;
use crate::mla::fmla;
use crate::neon::store_d::NeonStoreD;
use crate::neon::util::boring_neon_mixed_radix;
use crate::util::{DctConstants, mixed_radix_inner_twiddle, try_vec, validate_scratch};
use crate::{PxdctError, PxdctExecutor};
use num_traits::AsPrimitive;
use std::sync::Arc;

pub(crate) struct NeonDct2MixedRadix6d {
    inner_layer: Vec<NeonStoreD>,
    sixth_dct: Arc<dyn PxdctExecutor<f64> + Send + Sync>,
    inner_dct_scratch_size: usize,
    sixth_length: usize,
    execution_length: usize,
}

pub(crate) fn dct2_radix6_neon_groupd(len: usize) -> Vec<NeonStoreD> {
    let inner_layer_groups = len / 6;
    let simd_groups = inner_layer_groups.div_ceil(2);
    let mut inner_layer = Vec::with_capacity(simd_groups * 7);

    for g in 0..simd_groups {
        let mut re0 = [0f64; 2];
        let mut im0 = [0f64; 2];
        let mut re1 = [0f64; 2];
        let mut im1 = [0f64; 2];
        let mut re2 = [0f64; 2];
        let mut re3 = [0f64; 2];
        let mut im3 = [0f64; 2];

        for lane in 0..2 {
            let i = g * 2 + lane;
            if i < inner_layer_groups {
                let angle = (2. * i as f64 + 1.).as_();
                let t0 = mixed_radix_inner_twiddle(angle, len);
                let t1 = mixed_radix_inner_twiddle(2.0 * angle, len);
                let t2 = mixed_radix_inner_twiddle(3.0 * angle, len);
                let t3 = mixed_radix_inner_twiddle(5.0 * angle, len);

                re0[lane] = t0.re;
                im0[lane] = t0.im * f64::SQRT_3;

                re1[lane] = t1.re;
                im1[lane] = t1.im * f64::SQRT_3;

                re2[lane] = t2.re;

                re3[lane] = t3.re;
                im3[lane] = -t3.im * f64::SQRT_3;
            }
        }

        inner_layer.push(NeonStoreD::load(&re0));
        inner_layer.push(NeonStoreD::load(&im0));
        inner_layer.push(NeonStoreD::load(&re1));
        inner_layer.push(NeonStoreD::load(&im1));
        inner_layer.push(NeonStoreD::load(&re2));
        inner_layer.push(NeonStoreD::load(&re3));
        inner_layer.push(NeonStoreD::load(&im3));
    }
    inner_layer
}

impl NeonDct2MixedRadix6d {
    pub(crate) fn new(
        len: usize,
        sixth_dct: Arc<dyn PxdctExecutor<f64> + Send + Sync>,
    ) -> Result<NeonDct2MixedRadix6d, PxdctError> {
        assert_eq!(
            len,
            sixth_dct.length() * 6,
            "Invalid DCT was received, third size is not multiple of full size"
        );

        let sixth_dct_scratch_size = sixth_dct.scratch_size();
        let sixth_length = sixth_dct.length();

        Ok(NeonDct2MixedRadix6d {
            inner_layer: dct2_radix6_neon_groupd(len),
            sixth_dct,
            inner_dct_scratch_size: sixth_dct_scratch_size,
            execution_length: len,
            sixth_length,
        })
    }
}

impl NeonDct2MixedRadix6d {
    #[inline(always)]
    fn exec_block<S: BidirectionalStore<f64>, const N: usize>(
        &self,
        data: &mut S,
        a_buffer: &mut [f64],
        b_buffer: &mut [f64],
        c_buffer: &mut [f64],
        d_buffer: &mut [f64],
        e_buffer: &mut [f64],
        f_buffer: &mut [f64],
        twiddle_idx: usize,
        j: usize,
        s_n: usize,
        s_2n: usize,
        len: usize,
    ) {
        let ai = NeonStoreD::load_n::<N>(data.slice_from(j..));
        let mut bi = NeonStoreD::load_n::<N>(data.slice_from(s_n - j - N..));
        let ci = NeonStoreD::load_n::<N>(data.slice_from(s_n + j..));
        let mut di = NeonStoreD::load_n::<N>(data.slice_from(s_2n - j - N..));
        let ei = NeonStoreD::load_n::<N>(data.slice_from(s_2n + j..));
        let mut fi = NeonStoreD::load_n::<N>(data.slice_from(len - j - N..));

        bi = bi.reverse_n::<N>();
        di = di.reverse_n::<N>();
        fi = fi.reverse_n::<N>();

        let cos_sin_ai_re = unsafe { *self.inner_layer.get_unchecked(twiddle_idx) };
        let cos_sin_ai_im = unsafe { *self.inner_layer.get_unchecked(twiddle_idx + 1) };
        let cos_sin_2ai_re = unsafe { *self.inner_layer.get_unchecked(twiddle_idx + 2) };
        let cos_sin_2ai_im = unsafe { *self.inner_layer.get_unchecked(twiddle_idx + 3) };
        let cos_sin_3ai_re = unsafe { *self.inner_layer.get_unchecked(twiddle_idx + 4) };
        let cos_sin_5ai_re = unsafe { *self.inner_layer.get_unchecked(twiddle_idx + 5) };
        let cos_sin_5ai_im = unsafe { *self.inner_layer.get_unchecked(twiddle_idx + 6) };

        let s2 = bi + ei;
        let dcd = ci - di;
        let dbe = bi - ei;

        let ai2 = f64::TWO * ai;
        let fi2 = f64::TWO * fi;
        let scd = ci + di;

        let sdbedcd = dbe + dcd;
        let ai2dbedcd = ai2 + sdbedcd - fi2;
        let s2scd = s2 + scd;

        let a_comp = ai + s2scd + fi;
        let c_comp = ai2 - s2scd + fi2;
        let d_comp = f64::TWO * (ai - sdbedcd - fi);
        let dbedcd = dbe - dcd;

        let c_img = s2 - ci - di;
        let b_zet = dbedcd * cos_sin_ai_im;
        let c_zet = c_img * cos_sin_2ai_im;
        let f_zet = dbedcd * cos_sin_5ai_im;

        let e_comp = fmla(
            f64::TWO * cos_sin_2ai_re,
            fmla(c_comp, cos_sin_2ai_re, -c_zet),
            -c_comp,
        );

        unsafe {
            a_comp.write_n::<N>(a_buffer.get_unchecked_mut(j..));
            fmla(ai2dbedcd, cos_sin_ai_re, b_zet).write_n::<N>(b_buffer.get_unchecked_mut(j..));
            fmla(c_comp, cos_sin_2ai_re, c_zet).write_n::<N>(c_buffer.get_unchecked_mut(j..));
            (d_comp * cos_sin_3ai_re).write_n::<N>(d_buffer.get_unchecked_mut(j..));
            e_comp.write_n::<N>(e_buffer.get_unchecked_mut(j..));
            fmla(ai2dbedcd, cos_sin_5ai_re, f_zet).write_n::<N>(f_buffer.get_unchecked_mut(j..));
        }
    }

    #[inline(always)]
    fn execute_with_store<S: BidirectionalStore<f64>>(
        &self,
        data: &mut S,
        scratch: &mut [f64],
    ) -> Result<(), PxdctError> {
        let (scratch, inner_scratch) = scratch.split_at_mut(self.execution_length);

        let len = self.length();
        let sixth_length = self.sixth_length;
        let s_n = len / 3;
        let s_2n = 2 * len / 3;
        let (a_buffer, rem) = scratch.split_at_mut(sixth_length);
        let (b_buffer, rem) = rem.split_at_mut(sixth_length);
        let (c_buffer, rem) = rem.split_at_mut(sixth_length);
        let (d_buffer, rem) = rem.split_at_mut(sixth_length);
        let (e_buffer, rem) = rem.split_at_mut(sixth_length);
        let (f_buffer, _) = rem.split_at_mut(sixth_length);

        let mut j = 0usize;

        let mut twiddle_idx = 0usize;

        while j + 2 <= sixth_length {
            self.exec_block::<S, 2>(
                data,
                a_buffer,
                b_buffer,
                c_buffer,
                d_buffer,
                e_buffer,
                f_buffer,
                twiddle_idx,
                j,
                s_n,
                s_2n,
                len,
            );
            j += 2;
            twiddle_idx += 7;
        }

        let rem = sixth_length - j;

        if rem == 1 {
            self.exec_block::<S, 1>(
                data,
                a_buffer,
                b_buffer,
                c_buffer,
                d_buffer,
                e_buffer,
                f_buffer,
                twiddle_idx,
                j,
                s_n,
                s_2n,
                len,
            );
        }

        if a_buffer.len() > 1 {
            self.sixth_dct
                .execute_with_scratch(scratch, inner_scratch)?;
        }

        let (a_buffer, rem) = scratch.split_at_mut(sixth_length);
        let (b_buffer, rem) = rem.split_at_mut(sixth_length);
        let (c_buffer, rem) = rem.split_at_mut(sixth_length);
        let (d_buffer, rem) = rem.split_at_mut(sixth_length);
        let (e_buffer, rem) = rem.split_at_mut(sixth_length);
        let (f_buffer, _) = rem.split_at_mut(sixth_length);

        data[0] = a_buffer[0];
        let b0 = b_buffer[0] * f64::HALF;
        data[1] = b0;
        let c0 = c_buffer[0] * f64::HALF;
        data[2] = c0;
        let d0 = d_buffer[0] * f64::HALF;
        data[3] = d0;
        let e0 = e_buffer[0] * f64::HALF;
        data[4] = e0;
        let f0 = f_buffer[0] * f64::HALF;
        data[5] = f0;

        let mut b_diff = f0;
        let mut c_diff = e0;
        let mut e_diff = d0;
        let mut d_diff = c0;
        let mut f_diff = b0;

        for k in 1..sixth_length {
            let deferred_d_diff;
            let deferred_f_diff;
            unsafe {
                data[6 * k] = *a_buffer.get_unchecked(k);
            }
            unsafe {
                deferred_f_diff = *b_buffer.get_unchecked(k) - b_diff;
                data[6 * k + 1] = deferred_f_diff;
            }
            unsafe {
                deferred_d_diff = *c_buffer.get_unchecked(k) - c_diff;
                data[6 * k + 2] = deferred_d_diff;
            }
            unsafe {
                e_diff = *d_buffer.get_unchecked(k) - e_diff;
                data[6 * k + 3] = e_diff;
            }
            unsafe {
                let new_d = *e_buffer.get_unchecked(k) - d_diff;
                data[6 * k + 4] = new_d;
                c_diff = new_d;
                d_diff = deferred_d_diff;
            }
            unsafe {
                let new_f = *f_buffer.get_unchecked(k) - f_diff;
                b_diff = new_f;
                f_diff = deferred_f_diff;
                data[6 * k + 5] = new_f;
            }
        }
        Ok(())
    }
}

boring_neon_mixed_radix!(NeonDct2MixedRadix6d, f64);

#[cfg(test)]
mod tests {
    use super::*;
    use crate::butterflies::Dct2Butterfly6;
    use crate::tests::naive_dct2;

    #[test]
    fn test_radix6_dct2() {
        let mut input = vec![0.; 36];
        for (i, z) in input.iter_mut().enumerate() {
            *z = i as f64;
        }
        let reference_input = input.clone();
        let reference_input = naive_dct2(&reference_input);
        let bf = NeonDct2MixedRadix6d::new(36, Arc::new(Dct2Butterfly6::default())).unwrap();
        bf.execute(&mut input).unwrap();

        input
            .iter()
            .zip(reference_input.iter())
            .enumerate()
            .for_each(|(i, (&src, &r0))| {
                assert!(
                    (src - r0).abs() < 1e-3,
                    "Difference must be < {}, but it was {}, at position {i}",
                    1e-7,
                    (src - r0).abs()
                )
            });
    }
}