pxdct 0.3.2

/*
 * // Copyright (c) Radzivon Bartoshyk 1/2026. 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::avx::stored::AvxStoreD;
use crate::avx::util::{boring_avx_mixed_radix, fma};
use crate::bidirectional::BidirectionalStore;
use crate::dct4::radixq_dct4_rotation_twiddle;
use crate::util::{DctConstants, DctSample, try_vec, validate_scratch};
use crate::{PxdctError, PxdctExecutor};
use num_traits::{AsPrimitive, One};
use std::sync::Arc;

#[target_feature(enable = "avx2")]
pub(crate) fn dct4_radix_n_rotation_twiddles_avxd(
    q: usize,
    q_modules: usize,
    len: usize,
) -> Vec<AvxStoreD> {
    let main_q = q;
    let inner_groups = (main_q.saturating_sub(3)) / 2 + 1;

    let working_modules = q_modules;
    let main_groups = working_modules / 4;
    let has_remainder = !working_modules.is_multiple_of(4) as usize;
    let mut twiddles = Vec::with_capacity((main_groups + has_remainder) * 2 * inner_groups);

    let mut uk = 0usize;
    while uk + 4 <= working_modules {
        let k = uk;

        let mut array_re = [0.; 4];
        let mut array_im = [0.; 4];
        for m in 0..inner_groups {
            for i in 0..4 {
                let layer = radixq_dct4_rotation_twiddle(main_q, m, (k + i).as_(), len);
                array_re[i] = layer.re;
                array_im[i] = layer.im;
            }

            twiddles.push(AvxStoreD::load(array_re.as_ref()));
            twiddles.push(AvxStoreD::load(array_im.as_ref()));
        }

        uk += 4;
    }

    let remainder = working_modules - (working_modules / 4) * 4;
    if remainder > 0 {
        let k = uk;

        let mut array_re = [0.; 4];
        let mut array_im = [0.; 4];
        for m in 0..inner_groups {
            for i in 0..remainder {
                let layer = radixq_dct4_rotation_twiddle(main_q, m, (k + i).as_(), len);
                array_re[i] = layer.re;
                array_im[i] = layer.im;
            }

            twiddles.push(AvxStoreD::load(array_re.as_ref()));
            twiddles.push(AvxStoreD::load(array_im.as_ref()));
        }
    }

    twiddles
}

pub(crate) struct AvxDct4MixedRadix3d {
    inner_dct4: Arc<dyn PxdctExecutor<f64> + Send + Sync>,
    inner_dct_scratch_size: usize,
    rotation_twiddles: Vec<AvxStoreD>,
    execution_length: usize,
    q_modules: usize,
    s: usize,
}

impl AvxDct4MixedRadix3d {
    pub(crate) fn new(
        len: usize,
        dct4: Arc<dyn PxdctExecutor<f64> + Send + Sync>,
    ) -> Result<Self, PxdctError> {
        assert_eq!(
            dct4.length(),
            len / 3,
            "DCT-IV Mixed-Radix-3 length DCTs must be third of DCT-IV"
        );

        let inner_dct4_scratch_size = dct4.scratch_size();

        Ok(Self {
            inner_dct4: dct4,
            inner_dct_scratch_size: inner_dct4_scratch_size,
            execution_length: len,
            rotation_twiddles: unsafe { dct4_radix_n_rotation_twiddles_avxd(3, len / 3, len) },
            q_modules: len / 3,
            s: 2 * len / 3,
        })
    }
}

boring_avx_mixed_radix!(AvxDct4MixedRadix3d, f64);

impl AvxDct4MixedRadix3d {
    #[inline]
    #[target_feature(enable = "avx2", enable = "fma")]
    fn exec_block<S: BidirectionalStore<f64>, const N: usize>(
        &self,
        data: &mut S,
        a_buffer: &[f64],
        s_buffer: &[f64],
        c_buffer: &[f64],
        uk: usize,
        k: usize,
    ) {
        let c_v = AvxStoreD::load_n::<N>(unsafe { c_buffer.get_unchecked(k..) });
        let s_v =
            AvxStoreD::load_n::<N>(unsafe { s_buffer.get_unchecked(self.q_modules - k - N..) })
                .reverse_n::<N>();
        let a_v = AvxStoreD::load_n::<N>(unsafe { a_buffer.get_unchecked(k..) });

        let twiddle_re = unsafe { *self.rotation_twiddles.get_unchecked(uk) };
        let twiddle_im = unsafe { *self.rotation_twiddles.get_unchecked(uk + 1) };

        let mut u0 = fma(c_v, twiddle_re, s_v * twiddle_im);
        let mut u1 = u0;
        let mut v0 = fma(c_v, twiddle_im, -s_v * twiddle_re);

        u0 += a_v;
        u1 *= f64::HALF;
        v0 *= f64::SQRT_3_OVER_2;
        u1 = u1 - a_v;

        let uc0 = u1 - v0;
        let uc1 = u1 + v0;

        u0.write_n::<N>(data.slice_from_mut(k..));
        uc1.write_n::<N>(data.slice_from_mut(self.s + k..));
        uc0.reverse_n::<N>()
            .write_n::<N>(data.slice_from_mut(self.s - N - k..));
    }

    #[inline]
    #[target_feature(enable = "avx2", enable = "fma")]
    fn execute_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 q_modules = self.execution_length / 3;
        let (a_buffer, c_s_buffer) = scratch.split_at_mut(q_modules);
        let (c_buffer, s_buffer) = c_s_buffer.split_at_mut(q_modules);

        // Step 1: Decompose input into A (center), C (even-symmetric), S (odd-symmetric) buffers
        for (n, dst) in a_buffer.iter_mut().enumerate() {
            *dst = data[n * 3 + 1];
        }

        // Extract and combine symmetric pairs with sign alternation for S buffer
        for (m, (c_buffer, s_buffer)) in c_buffer
            .chunks_exact_mut(q_modules)
            .zip(s_buffer.chunks_exact_mut(q_modules))
            .enumerate()
        {
            let mut sign = f64::one();
            for (n, (c_dst, s_dst)) in c_buffer.iter_mut().zip(s_buffer.iter_mut()).enumerate() {
                let u0 = data[3 * n + m];
                let u1 = data[3 * n + 3 - m - 1];

                *c_dst = u0 + u1;
                *s_dst = (u0 - u1).mulsign(sign);

                sign = -sign;
            }
        }

        // Step 2: Apply DCT-IV to all buffers (A, C₀, C₁, S₀, S₁)
        self.inner_dct4
            .execute_with_scratch(scratch, inner_scratch)?;

        let (a_buffer, c_s_buffer) = scratch.split_at_mut(q_modules);
        let (c_buffer, s_buffer) = c_s_buffer.split_at_mut(q_modules);

        // Step 4: Handle rotation twiddles
        let mut k = 0usize;
        let mut uk = 0usize;

        while k + 4 <= q_modules {
            self.exec_block::<S, 4>(data, a_buffer, s_buffer, c_buffer, uk, k);
            k += 4;
            uk += 2;
        }

        let remainder = q_modules - k;
        if remainder == 3 {
            self.exec_block::<S, 3>(data, a_buffer, s_buffer, c_buffer, uk, k);
        } else if remainder == 2 {
            self.exec_block::<S, 2>(data, a_buffer, s_buffer, c_buffer, uk, k);
        } else if remainder == 1 {
            self.exec_block::<S, 1>(data, a_buffer, s_buffer, c_buffer, uk, k);
        }
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::dct4::Dct4Butterfly3;
    use crate::tests::naive_dct4;
    use crate::util::has_valid_avx;
    use rand::RngExt;

    #[test]
    fn test_split_dct4() {
        if !has_valid_avx() {
            return;
        }
        let mut input = vec![0.; 9];
        for z in input.iter_mut() {
            *z = rand::rng().random_range(1.0..2.0);
        }
        let mut input = vec![
            1.8842070837939089f64,
            1.744160875935288,
            1.0859464680821782,
            1.8842070837939089,
            1.744160875935288,
            1.0859464680821782,
            1.8842070837939089,
            1.744160875935288,
            1.0859464680821782,
        ];
        let reference_input0 = input.clone();
        let reference_input = naive_dct4(&reference_input0);
        let bf = AvxDct4MixedRadix3d::new(9, Arc::new(Dct4Butterfly3::default())).unwrap();
        bf.execute(&mut input).unwrap();
        input
            .iter()
            .zip(reference_input.iter())
            .enumerate()
            .for_each(|(i, (&src, &r0))| {
                if (src - r0).abs() > 1e-1 {
                    println!(
                        "Difference must be < {}, but it was {}, at position {i}",
                        1e-1,
                        (src - r0).abs()
                    )
                }
            });
    }
}