modules/audio_processing/utility/ooura_fft_sse2.cc

/*
 *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include "modules/audio_processing/utility/ooura_fft.h"

#include <emmintrin.h>

#include "modules/audio_processing/utility/ooura_fft_tables_common.h"
#include "modules/audio_processing/utility/ooura_fft_tables_neon_sse2.h"
#include "rtc_base/system/arch.h"

namespace webrtc {

#if defined(WEBRTC_ARCH_X86_FAMILY)

namespace {
// These intrinsics were unavailable before VS 2008.
// TODO(andrew): move to a common file.
#if defined(_MSC_VER) && _MSC_VER < 1500
static __inline __m128 _mm_castsi128_ps(__m128i a) {
  return *(__m128*)&a;
}
static __inline __m128i _mm_castps_si128(__m128 a) {
  return *(__m128i*)&a;
}
#endif

}  // namespace

void cft1st_128_SSE2(float* a) {
  const __m128 mm_swap_sign = _mm_load_ps(k_swap_sign);
  int j, k2;

  for (k2 = 0, j = 0; j < 128; j += 16, k2 += 4) {
    __m128 a00v = _mm_loadu_ps(&a[j + 0]);
    __m128 a04v = _mm_loadu_ps(&a[j + 4]);
    __m128 a08v = _mm_loadu_ps(&a[j + 8]);
    __m128 a12v = _mm_loadu_ps(&a[j + 12]);
    __m128 a01v = _mm_shuffle_ps(a00v, a08v, _MM_SHUFFLE(1, 0, 1, 0));
    __m128 a23v = _mm_shuffle_ps(a00v, a08v, _MM_SHUFFLE(3, 2, 3, 2));
    __m128 a45v = _mm_shuffle_ps(a04v, a12v, _MM_SHUFFLE(1, 0, 1, 0));
    __m128 a67v = _mm_shuffle_ps(a04v, a12v, _MM_SHUFFLE(3, 2, 3, 2));

    const __m128 wk1rv = _mm_load_ps(&rdft_wk1r[k2]);
    const __m128 wk1iv = _mm_load_ps(&rdft_wk1i[k2]);
    const __m128 wk2rv = _mm_load_ps(&rdft_wk2r[k2]);
    const __m128 wk2iv = _mm_load_ps(&rdft_wk2i[k2]);
    const __m128 wk3rv = _mm_load_ps(&rdft_wk3r[k2]);
    const __m128 wk3iv = _mm_load_ps(&rdft_wk3i[k2]);
    __m128 x0v = _mm_add_ps(a01v, a23v);
    const __m128 x1v = _mm_sub_ps(a01v, a23v);
    const __m128 x2v = _mm_add_ps(a45v, a67v);
    const __m128 x3v = _mm_sub_ps(a45v, a67v);
    __m128 x0w;
    a01v = _mm_add_ps(x0v, x2v);
    x0v = _mm_sub_ps(x0v, x2v);
    x0w = _mm_shuffle_ps(x0v, x0v, _MM_SHUFFLE(2, 3, 0, 1));
    {
      const __m128 a45_0v = _mm_mul_ps(wk2rv, x0v);
      const __m128 a45_1v = _mm_mul_ps(wk2iv, x0w);
      a45v = _mm_add_ps(a45_0v, a45_1v);
    }
    {
      __m128 a23_0v, a23_1v;
      const __m128 x3w = _mm_shuffle_ps(x3v, x3v, _MM_SHUFFLE(2, 3, 0, 1));
      const __m128 x3s = _mm_mul_ps(mm_swap_sign, x3w);
      x0v = _mm_add_ps(x1v, x3s);
      x0w = _mm_shuffle_ps(x0v, x0v, _MM_SHUFFLE(2, 3, 0, 1));
      a23_0v = _mm_mul_ps(wk1rv, x0v);
      a23_1v = _mm_mul_ps(wk1iv, x0w);
      a23v = _mm_add_ps(a23_0v, a23_1v);

      x0v = _mm_sub_ps(x1v, x3s);
      x0w = _mm_shuffle_ps(x0v, x0v, _MM_SHUFFLE(2, 3, 0, 1));
    }
    {
      const __m128 a67_0v = _mm_mul_ps(wk3rv, x0v);
      const __m128 a67_1v = _mm_mul_ps(wk3iv, x0w);
      a67v = _mm_add_ps(a67_0v, a67_1v);
    }

    a00v = _mm_shuffle_ps(a01v, a23v, _MM_SHUFFLE(1, 0, 1, 0));
    a04v = _mm_shuffle_ps(a45v, a67v, _MM_SHUFFLE(1, 0, 1, 0));
    a08v = _mm_shuffle_ps(a01v, a23v, _MM_SHUFFLE(3, 2, 3, 2));
    a12v = _mm_shuffle_ps(a45v, a67v, _MM_SHUFFLE(3, 2, 3, 2));
    _mm_storeu_ps(&a[j + 0], a00v);
    _mm_storeu_ps(&a[j + 4], a04v);
    _mm_storeu_ps(&a[j + 8], a08v);
    _mm_storeu_ps(&a[j + 12], a12v);
  }
}

void cftmdl_128_SSE2(float* a) {
  const int l = 8;
  const __m128 mm_swap_sign = _mm_load_ps(k_swap_sign);
  int j0;

  __m128 wk1rv = _mm_load_ps(cftmdl_wk1r);
  for (j0 = 0; j0 < l; j0 += 2) {
    const __m128i a_00 = _mm_loadl_epi64((__m128i*)&a[j0 + 0]);
    const __m128i a_08 = _mm_loadl_epi64((__m128i*)&a[j0 + 8]);
    const __m128i a_32 = _mm_loadl_epi64((__m128i*)&a[j0 + 32]);
    const __m128i a_40 = _mm_loadl_epi64((__m128i*)&a[j0 + 40]);
    const __m128 a_00_32 =
        _mm_shuffle_ps(_mm_castsi128_ps(a_00), _mm_castsi128_ps(a_32),
                       _MM_SHUFFLE(1, 0, 1, 0));
    const __m128 a_08_40 =
        _mm_shuffle_ps(_mm_castsi128_ps(a_08), _mm_castsi128_ps(a_40),
                       _MM_SHUFFLE(1, 0, 1, 0));
    __m128 x0r0_0i0_0r1_x0i1 = _mm_add_ps(a_00_32, a_08_40);
    const __m128 x1r0_1i0_1r1_x1i1 = _mm_sub_ps(a_00_32, a_08_40);

    const __m128i a_16 = _mm_loadl_epi64((__m128i*)&a[j0 + 16]);
    const __m128i a_24 = _mm_loadl_epi64((__m128i*)&a[j0 + 24]);
    const __m128i a_48 = _mm_loadl_epi64((__m128i*)&a[j0 + 48]);
    const __m128i a_56 = _mm_loadl_epi64((__m128i*)&a[j0 + 56]);
    const __m128 a_16_48 =
        _mm_shuffle_ps(_mm_castsi128_ps(a_16), _mm_castsi128_ps(a_48),
                       _MM_SHUFFLE(1, 0, 1, 0));
    const __m128 a_24_56 =
        _mm_shuffle_ps(_mm_castsi128_ps(a_24), _mm_castsi128_ps(a_56),
                       _MM_SHUFFLE(1, 0, 1, 0));
    const __m128 x2r0_2i0_2r1_x2i1 = _mm_add_ps(a_16_48, a_24_56);
    const __m128 x3r0_3i0_3r1_x3i1 = _mm_sub_ps(a_16_48, a_24_56);

    const __m128 xx0 = _mm_add_ps(x0r0_0i0_0r1_x0i1, x2r0_2i0_2r1_x2i1);
    const __m128 xx1 = _mm_sub_ps(x0r0_0i0_0r1_x0i1, x2r0_2i0_2r1_x2i1);

    const __m128 x3i0_3r0_3i1_x3r1 = _mm_castsi128_ps(_mm_shuffle_epi32(
        _mm_castps_si128(x3r0_3i0_3r1_x3i1), _MM_SHUFFLE(2, 3, 0, 1)));
    const __m128 x3_swapped = _mm_mul_ps(mm_swap_sign, x3i0_3r0_3i1_x3r1);
    const __m128 x1_x3_add = _mm_add_ps(x1r0_1i0_1r1_x1i1, x3_swapped);
    const __m128 x1_x3_sub = _mm_sub_ps(x1r0_1i0_1r1_x1i1, x3_swapped);

    const __m128 yy0 =
        _mm_shuffle_ps(x1_x3_add, x1_x3_sub, _MM_SHUFFLE(2, 2, 2, 2));
    const __m128 yy1 =
        _mm_shuffle_ps(x1_x3_add, x1_x3_sub, _MM_SHUFFLE(3, 3, 3, 3));
    const __m128 yy2 = _mm_mul_ps(mm_swap_sign, yy1);
    const __m128 yy3 = _mm_add_ps(yy0, yy2);
    const __m128 yy4 = _mm_mul_ps(wk1rv, yy3);

    _mm_storel_epi64((__m128i*)&a[j0 + 0], _mm_castps_si128(xx0));
    _mm_storel_epi64(
        (__m128i*)&a[j0 + 32],
        _mm_shuffle_epi32(_mm_castps_si128(xx0), _MM_SHUFFLE(3, 2, 3, 2)));

    _mm_storel_epi64((__m128i*)&a[j0 + 16], _mm_castps_si128(xx1));
    _mm_storel_epi64(
        (__m128i*)&a[j0 + 48],
        _mm_shuffle_epi32(_mm_castps_si128(xx1), _MM_SHUFFLE(2, 3, 2, 3)));
    a[j0 + 48] = -a[j0 + 48];

    _mm_storel_epi64((__m128i*)&a[j0 + 8], _mm_castps_si128(x1_x3_add));
    _mm_storel_epi64((__m128i*)&a[j0 + 24], _mm_castps_si128(x1_x3_sub));

    _mm_storel_epi64((__m128i*)&a[j0 + 40], _mm_castps_si128(yy4));
    _mm_storel_epi64(
        (__m128i*)&a[j0 + 56],
        _mm_shuffle_epi32(_mm_castps_si128(yy4), _MM_SHUFFLE(2, 3, 2, 3)));
  }

  {
    int k = 64;
    int k1 = 2;
    int k2 = 2 * k1;
    const __m128 wk2rv = _mm_load_ps(&rdft_wk2r[k2 + 0]);
    const __m128 wk2iv = _mm_load_ps(&rdft_wk2i[k2 + 0]);
    const __m128 wk1iv = _mm_load_ps(&rdft_wk1i[k2 + 0]);
    const __m128 wk3rv = _mm_load_ps(&rdft_wk3r[k2 + 0]);
    const __m128 wk3iv = _mm_load_ps(&rdft_wk3i[k2 + 0]);
    wk1rv = _mm_load_ps(&rdft_wk1r[k2 + 0]);
    for (j0 = k; j0 < l + k; j0 += 2) {
      const __m128i a_00 = _mm_loadl_epi64((__m128i*)&a[j0 + 0]);
      const __m128i a_08 = _mm_loadl_epi64((__m128i*)&a[j0 + 8]);
      const __m128i a_32 = _mm_loadl_epi64((__m128i*)&a[j0 + 32]);
      const __m128i a_40 = _mm_loadl_epi64((__m128i*)&a[j0 + 40]);
      const __m128 a_00_32 =
          _mm_shuffle_ps(_mm_castsi128_ps(a_00), _mm_castsi128_ps(a_32),
                         _MM_SHUFFLE(1, 0, 1, 0));
      const __m128 a_08_40 =
          _mm_shuffle_ps(_mm_castsi128_ps(a_08), _mm_castsi128_ps(a_40),
                         _MM_SHUFFLE(1, 0, 1, 0));
      __m128 x0r0_0i0_0r1_x0i1 = _mm_add_ps(a_00_32, a_08_40);
      const __m128 x1r0_1i0_1r1_x1i1 = _mm_sub_ps(a_00_32, a_08_40);

      const __m128i a_16 = _mm_loadl_epi64((__m128i*)&a[j0 + 16]);
      const __m128i a_24 = _mm_loadl_epi64((__m128i*)&a[j0 + 24]);
      const __m128i a_48 = _mm_loadl_epi64((__m128i*)&a[j0 + 48]);
      const __m128i a_56 = _mm_loadl_epi64((__m128i*)&a[j0 + 56]);
      const __m128 a_16_48 =
          _mm_shuffle_ps(_mm_castsi128_ps(a_16), _mm_castsi128_ps(a_48),
                         _MM_SHUFFLE(1, 0, 1, 0));
      const __m128 a_24_56 =
          _mm_shuffle_ps(_mm_castsi128_ps(a_24), _mm_castsi128_ps(a_56),
                         _MM_SHUFFLE(1, 0, 1, 0));
      const __m128 x2r0_2i0_2r1_x2i1 = _mm_add_ps(a_16_48, a_24_56);
      const __m128 x3r0_3i0_3r1_x3i1 = _mm_sub_ps(a_16_48, a_24_56);

      const __m128 xx = _mm_add_ps(x0r0_0i0_0r1_x0i1, x2r0_2i0_2r1_x2i1);
      const __m128 xx1 = _mm_sub_ps(x0r0_0i0_0r1_x0i1, x2r0_2i0_2r1_x2i1);
      const __m128 xx2 = _mm_mul_ps(xx1, wk2rv);
      const __m128 xx3 = _mm_mul_ps(
          wk2iv, _mm_castsi128_ps(_mm_shuffle_epi32(_mm_castps_si128(xx1),
                                                    _MM_SHUFFLE(2, 3, 0, 1))));
      const __m128 xx4 = _mm_add_ps(xx2, xx3);

      const __m128 x3i0_3r0_3i1_x3r1 = _mm_castsi128_ps(_mm_shuffle_epi32(
          _mm_castps_si128(x3r0_3i0_3r1_x3i1), _MM_SHUFFLE(2, 3, 0, 1)));
      const __m128 x3_swapped = _mm_mul_ps(mm_swap_sign, x3i0_3r0_3i1_x3r1);
      const __m128 x1_x3_add = _mm_add_ps(x1r0_1i0_1r1_x1i1, x3_swapped);
      const __m128 x1_x3_sub = _mm_sub_ps(x1r0_1i0_1r1_x1i1, x3_swapped);

      const __m128 xx10 = _mm_mul_ps(x1_x3_add, wk1rv);
      const __m128 xx11 = _mm_mul_ps(
          wk1iv, _mm_castsi128_ps(_mm_shuffle_epi32(_mm_castps_si128(x1_x3_add),
                                                    _MM_SHUFFLE(2, 3, 0, 1))));
      const __m128 xx12 = _mm_add_ps(xx10, xx11);

      const __m128 xx20 = _mm_mul_ps(x1_x3_sub, wk3rv);
      const __m128 xx21 = _mm_mul_ps(
          wk3iv, _mm_castsi128_ps(_mm_shuffle_epi32(_mm_castps_si128(x1_x3_sub),
                                                    _MM_SHUFFLE(2, 3, 0, 1))));
      const __m128 xx22 = _mm_add_ps(xx20, xx21);

      _mm_storel_epi64((__m128i*)&a[j0 + 0], _mm_castps_si128(xx));
      _mm_storel_epi64(
          (__m128i*)&a[j0 + 32],
          _mm_shuffle_epi32(_mm_castps_si128(xx), _MM_SHUFFLE(3, 2, 3, 2)));

      _mm_storel_epi64((__m128i*)&a[j0 + 16], _mm_castps_si128(xx4));
      _mm_storel_epi64(
          (__m128i*)&a[j0 + 48],
          _mm_shuffle_epi32(_mm_castps_si128(xx4), _MM_SHUFFLE(3, 2, 3, 2)));

      _mm_storel_epi64((__m128i*)&a[j0 + 8], _mm_castps_si128(xx12));
      _mm_storel_epi64(
          (__m128i*)&a[j0 + 40],
          _mm_shuffle_epi32(_mm_castps_si128(xx12), _MM_SHUFFLE(3, 2, 3, 2)));

      _mm_storel_epi64((__m128i*)&a[j0 + 24], _mm_castps_si128(xx22));
      _mm_storel_epi64(
          (__m128i*)&a[j0 + 56],
          _mm_shuffle_epi32(_mm_castps_si128(xx22), _MM_SHUFFLE(3, 2, 3, 2)));
    }
  }
}

void rftfsub_128_SSE2(float* a) {
  const float* c = rdft_w + 32;
  int j1, j2, k1, k2;
  float wkr, wki, xr, xi, yr, yi;

  static const ALIGN16_BEG float ALIGN16_END k_half[4] = {0.5f, 0.5f, 0.5f,
                                                          0.5f};
  const __m128 mm_half = _mm_load_ps(k_half);

  // Vectorized code (four at once).
  //    Note: commented number are indexes for the first iteration of the loop.
  for (j1 = 1, j2 = 2; j2 + 7 < 64; j1 += 4, j2 += 8) {
    // Load 'wk'.
    const __m128 c_j1 = _mm_loadu_ps(&c[j1]);       //  1,  2,  3,  4,
    const __m128 c_k1 = _mm_loadu_ps(&c[29 - j1]);  // 28, 29, 30, 31,
    const __m128 wkrt = _mm_sub_ps(mm_half, c_k1);  // 28, 29, 30, 31,
    const __m128 wkr_ =
        _mm_shuffle_ps(wkrt, wkrt, _MM_SHUFFLE(0, 1, 2, 3));  // 31, 30, 29, 28,
    const __m128 wki_ = c_j1;                                 //  1,  2,  3,  4,
    // Load and shuffle 'a'.
    const __m128 a_j2_0 = _mm_loadu_ps(&a[0 + j2]);    //   2,   3,   4,   5,
    const __m128 a_j2_4 = _mm_loadu_ps(&a[4 + j2]);    //   6,   7,   8,   9,
    const __m128 a_k2_0 = _mm_loadu_ps(&a[122 - j2]);  // 120, 121, 122, 123,
    const __m128 a_k2_4 = _mm_loadu_ps(&a[126 - j2]);  // 124, 125, 126, 127,
    const __m128 a_j2_p0 = _mm_shuffle_ps(
        a_j2_0, a_j2_4, _MM_SHUFFLE(2, 0, 2, 0));  //   2,   4,   6,   8,
    const __m128 a_j2_p1 = _mm_shuffle_ps(
        a_j2_0, a_j2_4, _MM_SHUFFLE(3, 1, 3, 1));  //   3,   5,   7,   9,
    const __m128 a_k2_p0 = _mm_shuffle_ps(
        a_k2_4, a_k2_0, _MM_SHUFFLE(0, 2, 0, 2));  // 126, 124, 122, 120,
    const __m128 a_k2_p1 = _mm_shuffle_ps(
        a_k2_4, a_k2_0, _MM_SHUFFLE(1, 3, 1, 3));  // 127, 125, 123, 121,
    // Calculate 'x'.
    const __m128 xr_ = _mm_sub_ps(a_j2_p0, a_k2_p0);
    // 2-126, 4-124, 6-122, 8-120,
    const __m128 xi_ = _mm_add_ps(a_j2_p1, a_k2_p1);
    // 3-127, 5-125, 7-123, 9-121,
    // Calculate product into 'y'.
    //    yr = wkr * xr - wki * xi;
    //    yi = wkr * xi + wki * xr;
    const __m128 a_ = _mm_mul_ps(wkr_, xr_);
    const __m128 b_ = _mm_mul_ps(wki_, xi_);
    const __m128 c_ = _mm_mul_ps(wkr_, xi_);
    const __m128 d_ = _mm_mul_ps(wki_, xr_);
    const __m128 yr_ = _mm_sub_ps(a_, b_);  // 2-126, 4-124, 6-122, 8-120,
    const __m128 yi_ = _mm_add_ps(c_, d_);  // 3-127, 5-125, 7-123, 9-121,
                                            // Update 'a'.
                                            //    a[j2 + 0] -= yr;
                                            //    a[j2 + 1] -= yi;
                                            //    a[k2 + 0] += yr;
    //    a[k2 + 1] -= yi;
    const __m128 a_j2_p0n = _mm_sub_ps(a_j2_p0, yr_);  //   2,   4,   6,   8,
    const __m128 a_j2_p1n = _mm_sub_ps(a_j2_p1, yi_);  //   3,   5,   7,   9,
    const __m128 a_k2_p0n = _mm_add_ps(a_k2_p0, yr_);  // 126, 124, 122, 120,
    const __m128 a_k2_p1n = _mm_sub_ps(a_k2_p1, yi_);  // 127, 125, 123, 121,
    // Shuffle in right order and store.
    const __m128 a_j2_0n = _mm_unpacklo_ps(a_j2_p0n, a_j2_p1n);
    //   2,   3,   4,   5,
    const __m128 a_j2_4n = _mm_unpackhi_ps(a_j2_p0n, a_j2_p1n);
    //   6,   7,   8,   9,
    const __m128 a_k2_0nt = _mm_unpackhi_ps(a_k2_p0n, a_k2_p1n);
    // 122, 123, 120, 121,
    const __m128 a_k2_4nt = _mm_unpacklo_ps(a_k2_p0n, a_k2_p1n);
    // 126, 127, 124, 125,
    const __m128 a_k2_0n = _mm_shuffle_ps(
        a_k2_0nt, a_k2_0nt, _MM_SHUFFLE(1, 0, 3, 2));  // 120, 121, 122, 123,
    const __m128 a_k2_4n = _mm_shuffle_ps(
        a_k2_4nt, a_k2_4nt, _MM_SHUFFLE(1, 0, 3, 2));  // 124, 125, 126, 127,
    _mm_storeu_ps(&a[0 + j2], a_j2_0n);
    _mm_storeu_ps(&a[4 + j2], a_j2_4n);
    _mm_storeu_ps(&a[122 - j2], a_k2_0n);
    _mm_storeu_ps(&a[126 - j2], a_k2_4n);
  }
  // Scalar code for the remaining items.
  for (; j2 < 64; j1 += 1, j2 += 2) {
    k2 = 128 - j2;
    k1 = 32 - j1;
    wkr = 0.5f - c[k1];
    wki = c[j1];
    xr = a[j2 + 0] - a[k2 + 0];
    xi = a[j2 + 1] + a[k2 + 1];
    yr = wkr * xr - wki * xi;
    yi = wkr * xi + wki * xr;
    a[j2 + 0] -= yr;
    a[j2 + 1] -= yi;
    a[k2 + 0] += yr;
    a[k2 + 1] -= yi;
  }
}

void rftbsub_128_SSE2(float* a) {
  const float* c = rdft_w + 32;
  int j1, j2, k1, k2;
  float wkr, wki, xr, xi, yr, yi;

  static const ALIGN16_BEG float ALIGN16_END k_half[4] = {0.5f, 0.5f, 0.5f,
                                                          0.5f};
  const __m128 mm_half = _mm_load_ps(k_half);

  a[1] = -a[1];
  // Vectorized code (four at once).
  //    Note: commented number are indexes for the first iteration of the loop.
  for (j1 = 1, j2 = 2; j2 + 7 < 64; j1 += 4, j2 += 8) {
    // Load 'wk'.
    const __m128 c_j1 = _mm_loadu_ps(&c[j1]);       //  1,  2,  3,  4,
    const __m128 c_k1 = _mm_loadu_ps(&c[29 - j1]);  // 28, 29, 30, 31,
    const __m128 wkrt = _mm_sub_ps(mm_half, c_k1);  // 28, 29, 30, 31,
    const __m128 wkr_ =
        _mm_shuffle_ps(wkrt, wkrt, _MM_SHUFFLE(0, 1, 2, 3));  // 31, 30, 29, 28,
    const __m128 wki_ = c_j1;                                 //  1,  2,  3,  4,
    // Load and shuffle 'a'.
    const __m128 a_j2_0 = _mm_loadu_ps(&a[0 + j2]);    //   2,   3,   4,   5,
    const __m128 a_j2_4 = _mm_loadu_ps(&a[4 + j2]);    //   6,   7,   8,   9,
    const __m128 a_k2_0 = _mm_loadu_ps(&a[122 - j2]);  // 120, 121, 122, 123,
    const __m128 a_k2_4 = _mm_loadu_ps(&a[126 - j2]);  // 124, 125, 126, 127,
    const __m128 a_j2_p0 = _mm_shuffle_ps(
        a_j2_0, a_j2_4, _MM_SHUFFLE(2, 0, 2, 0));  //   2,   4,   6,   8,
    const __m128 a_j2_p1 = _mm_shuffle_ps(
        a_j2_0, a_j2_4, _MM_SHUFFLE(3, 1, 3, 1));  //   3,   5,   7,   9,
    const __m128 a_k2_p0 = _mm_shuffle_ps(
        a_k2_4, a_k2_0, _MM_SHUFFLE(0, 2, 0, 2));  // 126, 124, 122, 120,
    const __m128 a_k2_p1 = _mm_shuffle_ps(
        a_k2_4, a_k2_0, _MM_SHUFFLE(1, 3, 1, 3));  // 127, 125, 123, 121,
    // Calculate 'x'.
    const __m128 xr_ = _mm_sub_ps(a_j2_p0, a_k2_p0);
    // 2-126, 4-124, 6-122, 8-120,
    const __m128 xi_ = _mm_add_ps(a_j2_p1, a_k2_p1);
    // 3-127, 5-125, 7-123, 9-121,
    // Calculate product into 'y'.
    //    yr = wkr * xr + wki * xi;
    //    yi = wkr * xi - wki * xr;
    const __m128 a_ = _mm_mul_ps(wkr_, xr_);
    const __m128 b_ = _mm_mul_ps(wki_, xi_);
    const __m128 c_ = _mm_mul_ps(wkr_, xi_);
    const __m128 d_ = _mm_mul_ps(wki_, xr_);
    const __m128 yr_ = _mm_add_ps(a_, b_);  // 2-126, 4-124, 6-122, 8-120,
    const __m128 yi_ = _mm_sub_ps(c_, d_);  // 3-127, 5-125, 7-123, 9-121,
                                            // Update 'a'.
                                            //    a[j2 + 0] = a[j2 + 0] - yr;
                                            //    a[j2 + 1] = yi - a[j2 + 1];
                                            //    a[k2 + 0] = yr + a[k2 + 0];
    //    a[k2 + 1] = yi - a[k2 + 1];
    const __m128 a_j2_p0n = _mm_sub_ps(a_j2_p0, yr_);  //   2,   4,   6,   8,
    const __m128 a_j2_p1n = _mm_sub_ps(yi_, a_j2_p1);  //   3,   5,   7,   9,
    const __m128 a_k2_p0n = _mm_add_ps(a_k2_p0, yr_);  // 126, 124, 122, 120,
    const __m128 a_k2_p1n = _mm_sub_ps(yi_, a_k2_p1);  // 127, 125, 123, 121,
    // Shuffle in right order and store.
    const __m128 a_j2_0n = _mm_unpacklo_ps(a_j2_p0n, a_j2_p1n);
    //   2,   3,   4,   5,
    const __m128 a_j2_4n = _mm_unpackhi_ps(a_j2_p0n, a_j2_p1n);
    //   6,   7,   8,   9,
    const __m128 a_k2_0nt = _mm_unpackhi_ps(a_k2_p0n, a_k2_p1n);
    // 122, 123, 120, 121,
    const __m128 a_k2_4nt = _mm_unpacklo_ps(a_k2_p0n, a_k2_p1n);
    // 126, 127, 124, 125,
    const __m128 a_k2_0n = _mm_shuffle_ps(
        a_k2_0nt, a_k2_0nt, _MM_SHUFFLE(1, 0, 3, 2));  // 120, 121, 122, 123,
    const __m128 a_k2_4n = _mm_shuffle_ps(
        a_k2_4nt, a_k2_4nt, _MM_SHUFFLE(1, 0, 3, 2));  // 124, 125, 126, 127,
    _mm_storeu_ps(&a[0 + j2], a_j2_0n);
    _mm_storeu_ps(&a[4 + j2], a_j2_4n);
    _mm_storeu_ps(&a[122 - j2], a_k2_0n);
    _mm_storeu_ps(&a[126 - j2], a_k2_4n);
  }
  // Scalar code for the remaining items.
  for (; j2 < 64; j1 += 1, j2 += 2) {
    k2 = 128 - j2;
    k1 = 32 - j1;
    wkr = 0.5f - c[k1];
    wki = c[j1];
    xr = a[j2 + 0] - a[k2 + 0];
    xi = a[j2 + 1] + a[k2 + 1];
    yr = wkr * xr + wki * xi;
    yi = wkr * xi - wki * xr;
    a[j2 + 0] = a[j2 + 0] - yr;
    a[j2 + 1] = yi - a[j2 + 1];
    a[k2 + 0] = yr + a[k2 + 0];
    a[k2 + 1] = yi - a[k2 + 1];
  }
  a[65] = -a[65];
}
#endif

}  // namespace webrtc