libgav1/src/dsp/convolve.inc

// Copyright 2020 The libgav1 Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Constants and utility functions used for convolve implementations.
// This will be included inside an anonymous namespace on files where these are
// necessary.

int GetNumTapsInFilter(const int filter_index) {
  if (filter_index < 2) {
    // Despite the names these only use 6 taps.
    // kInterpolationFilterEightTap
    // kInterpolationFilterEightTapSmooth
    return 6;
  }

  if (filter_index == 2) {
    // kInterpolationFilterEightTapSharp
    return 8;
  }

  if (filter_index == 3) {
    // kInterpolationFilterBilinear
    return 2;
  }

  assert(filter_index > 3);
  // For small sizes (width/height <= 4) the large filters are replaced with 4
  // tap options.
  // If the original filters were |kInterpolationFilterEightTap| or
  // |kInterpolationFilterEightTapSharp| then it becomes
  // |kInterpolationFilterSwitchable|.
  // If it was |kInterpolationFilterEightTapSmooth| then it becomes an unnamed 4
  // tap filter.
  return 4;
}

constexpr int kIntermediateStride = kMaxSuperBlockSizeInPixels;
constexpr int kHorizontalOffset = 3;
constexpr int kFilterIndexShift = 6;