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// Copyright 2005 Google Inc. All Rights Reserved.
// 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
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS-IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
// Author: (Eric Veach)
namespace S2 {
namespace internal {
// The canonical Hilbert traversal order looks like an inverted 'U':
// the subcells are visited in the order (0,0), (0,1), (1,1), (1,0).
// The following tables encode the traversal order for various
// orientations of the Hilbert curve (axes swapped and/or directions
// of the axes reversed).
// Together these flags define a cell orientation. If 'kSwapMask'
// is true, then canonical traversal order is flipped around the
// diagonal (i.e. i and j are swapped with each other). If
// 'kInvertMask' is true, then the traversal order is rotated by 180
// degrees (i.e. the bits of i and j are inverted, or equivalently,
// the axis directions are reversed).
int constexpr kSwapMask = 0x01;
int constexpr kInvertMask = 0x02;
// kIJtoPos[orientation][ij] -> pos
// Given a cell orientation and the (i,j)-index of a subcell (0=(0,0),
// 1=(0,1), 2=(1,0), 3=(1,1)), return the order in which this subcell is
// visited by the Hilbert curve (a position in the range [0..3]).
extern int const kIJtoPos[4][4];
// kPosToIJ[orientation][pos] -> ij
// Return the (i,j) index of the subcell at the given position 'pos' in the
// Hilbert curve traversal order with the given orientation. This is the
// inverse of the previous table:
// kPosToIJ[r][kIJtoPos[r][ij]] == ij
extern int const kPosToIJ[4][4];
// kPosToOrientation[pos] -> orientation_modifier
// Return a modifier indicating how the orientation of the child subcell
// with the given traversal position [0..3] is related to the orientation
// of the parent cell. The modifier should be XOR-ed with the parent
// orientation to obtain the curve orientation in the child.
extern int const kPosToOrientation[4];
// The U,V,W axes for each face.
extern double const kFaceUVWAxes[6][3][3];
// The precomputed neighbors of each face (see GetUVWFace).
extern int const kFaceUVWFaces[6][3][2];
} // namespace internal
} // namespace S2