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Diffstat (limited to '')
-rw-r--r-- | third_party/jpeg-xl/lib/jxl/enc_linalg.cc | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/third_party/jpeg-xl/lib/jxl/enc_linalg.cc b/third_party/jpeg-xl/lib/jxl/enc_linalg.cc new file mode 100644 index 0000000000..fe2090a909 --- /dev/null +++ b/third_party/jpeg-xl/lib/jxl/enc_linalg.cc @@ -0,0 +1,52 @@ +// Copyright (c) the JPEG XL 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. + +#include "lib/jxl/enc_linalg.h" + +#include <cmath> + +#include "lib/jxl/base/compiler_specific.h" +#include "lib/jxl/base/status.h" + +namespace jxl { + +void ConvertToDiagonal(const ImageD& A, ImageD* const JXL_RESTRICT diag, + ImageD* const JXL_RESTRICT U) { +#if JXL_ENABLE_ASSERT + JXL_ASSERT(A.xsize() == 2); + JXL_ASSERT(A.ysize() == 2); + JXL_ASSERT(std::abs(A.Row(0)[1] - A.Row(1)[0]) < 1e-15); +#endif + + if (std::abs(A.ConstRow(0)[1]) < 1e-15) { + // Already diagonal. + diag->Row(0)[0] = A.ConstRow(0)[0]; + diag->Row(0)[1] = A.ConstRow(1)[1]; + U->Row(0)[0] = U->Row(1)[1] = 1.0; + U->Row(0)[1] = U->Row(1)[0] = 0.0; + return; + } + double b = -(A.Row(0)[0] + A.Row(1)[1]); + double c = A.Row(0)[0] * A.Row(1)[1] - A.Row(0)[1] * A.Row(0)[1]; + double d = b * b - 4.0 * c; + double sqd = std::sqrt(d); + double l1 = (-b - sqd) * 0.5; + double l2 = (-b + sqd) * 0.5; + + double v1[2] = {A.Row(0)[0] - l1, A.Row(1)[0]}; + double v1n = 1.0 / std::hypot(v1[0], v1[1]); + v1[0] = v1[0] * v1n; + v1[1] = v1[1] * v1n; + + diag->Row(0)[0] = l1; + diag->Row(0)[1] = l2; + + U->Row(0)[0] = v1[1]; + U->Row(0)[1] = -v1[0]; + U->Row(1)[0] = v1[0]; + U->Row(1)[1] = v1[1]; +} + +} // namespace jxl |