src/cs16-bfly4/samples1-scalar.c

// Copyright 2022 Google LLC
//
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree.

#include <assert.h>
#include <stddef.h>
#include <stdint.h>

#include <xnnpack/math.h>
#include <xnnpack/fft.h>


void xnn_cs16_bfly4_samples1_ukernel__scalar(
    size_t samples,
    int16_t* data,
    const size_t stride,
    const int16_t* twiddle)
{
  assert(samples == 1);
  assert(data != NULL);
  assert(stride != 0);
  assert(twiddle != NULL);

  int32_t vout0r = (int32_t) data[0];
  int32_t vout0i = (int32_t) data[1];
  int32_t vout1r = (int32_t) data[2];
  int32_t vout1i = (int32_t) data[3];
  int32_t vout2r = (int32_t) data[4];
  int32_t vout2i = (int32_t) data[5];
  int32_t vout3r = (int32_t) data[6];
  int32_t vout3i = (int32_t) data[7];

  // Note 32767 / 4 = 8191.  Should be 8192.
  vout0r = math_asr_s32(vout0r * 8191 + 16384, 15);
  vout0i = math_asr_s32(vout0i * 8191 + 16384, 15);
  vout1r = math_asr_s32(vout1r * 8191 + 16384, 15);
  vout1i = math_asr_s32(vout1i * 8191 + 16384, 15);
  vout2r = math_asr_s32(vout2r * 8191 + 16384, 15);
  vout2i = math_asr_s32(vout2i * 8191 + 16384, 15);
  vout3r = math_asr_s32(vout3r * 8191 + 16384, 15);
  vout3i = math_asr_s32(vout3i * 8191 + 16384, 15);

  const int32_t vtmp5r = vout0r - vout2r;
  const int32_t vtmp5i = vout0i - vout2i;
  vout0r += vout2r;
  vout0i += vout2i;
  const int32_t vtmp3r = vout1r + vout3r;
  const int32_t vtmp3i = vout1i + vout3i;
  const int32_t vtmp4r = vout1r - vout3r;
  const int32_t vtmp4i = vout1i - vout3i;
  vout2r = vout0r - vtmp3r;
  vout2i = vout0i - vtmp3i;

  vout0r += vtmp3r;
  vout0i += vtmp3i;

  vout1r = vtmp5r + vtmp4i;
  vout1i = vtmp5i - vtmp4r;
  vout3r = vtmp5r - vtmp4i;
  vout3i = vtmp5i + vtmp4r;

  data[0] = (int16_t) vout0r;
  data[1] = (int16_t) vout0i;
  data[2] = (int16_t) vout1r;
  data[3] = (int16_t) vout1i;
  data[4] = (int16_t) vout2r;
  data[5] = (int16_t) vout2i;
  data[6] = (int16_t) vout3r;
  data[7] = (int16_t) vout3i;
}