1 files changed, 108 insertions, 0 deletions
diff --git a/media/libjxl/src/lib/jxl/ac_strategy.cc b/media/libjxl/src/lib/jxl/ac_strategy.cc
new file mode 100644
index 0000000000..ada3bcb6f5
--- /dev/null
+++ b/media/libjxl/src/lib/jxl/ac_strategy.cc
@@ -0,0 +1,108 @@
+// 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/ac_strategy.h"
+
+#include <string.h>
+
+#include <algorithm>
+#include <numeric>  // iota
+#include <type_traits>
+#include <utility>
+
+#include "lib/jxl/base/bits.h"
+#include "lib/jxl/base/profiler.h"
+#include "lib/jxl/common.h"
+#include "lib/jxl/image_ops.h"
+
+namespace jxl {
+
+// Tries to generalize zig-zag order to non-square blocks. Surprisingly, in
+// square block frequency along the (i + j == const) diagonals is roughly the
+// same. For historical reasons, consecutive diagonals are traversed
+// in alternating directions - so called "zig-zag" (or "snake") order.
+template <bool is_lut>
+static void CoeffOrderAndLut(AcStrategy acs, coeff_order_t* out) {
+  size_t cx = acs.covered_blocks_x();
+  size_t cy = acs.covered_blocks_y();
+  CoefficientLayout(&cy, &cx);
+
+  // CoefficientLayout ensures cx >= cy.
+  // We compute the zigzag order for a cx x cx block, then discard all the
+  // lines that are not multiple of the ratio between cx and cy.
+  size_t xs = cx / cy;
+  size_t xsm = xs - 1;
+  size_t xss = CeilLog2Nonzero(xs);
+  // First half of the block
+  size_t cur = cx * cy;
+  for (size_t i = 0; i < cx * kBlockDim; i++) {
+    for (size_t j = 0; j <= i; j++) {
+      size_t x = j;
+      size_t y = i - j;
+      if (i % 2) std::swap(x, y);
+      if ((y & xsm) != 0) continue;
+      y >>= xss;
+      size_t val = 0;
+      if (x < cx && y < cy) {
+        val = y * cx + x;
+      } else {
+        val = cur++;
+      }
+      if (is_lut) {
+        out[y * cx * kBlockDim + x] = val;
+      } else {
+        out[val] = y * cx * kBlockDim + x;
+      }
+    }
+  }
+  // Second half
+  for (size_t ip = cx * kBlockDim - 1; ip > 0; ip--) {
+    size_t i = ip - 1;
+    for (size_t j = 0; j <= i; j++) {
+      size_t x = cx * kBlockDim - 1 - (i - j);
+      size_t y = cx * kBlockDim - 1 - j;
+      if (i % 2) std::swap(x, y);
+      if ((y & xsm) != 0) continue;
+      y >>= xss;
+      size_t val = cur++;
+      if (is_lut) {
+        out[y * cx * kBlockDim + x] = val;
+      } else {
+        out[val] = y * cx * kBlockDim + x;
+      }
+    }
+  }
+}
+
+void AcStrategy::ComputeNaturalCoeffOrder(coeff_order_t* order) const {
+  CoeffOrderAndLut</*is_lut=*/false>(*this, order);
+}
+void AcStrategy::ComputeNaturalCoeffOrderLut(coeff_order_t* lut) const {
+  CoeffOrderAndLut</*is_lut=*/true>(*this, lut);
+}
+
+// These definitions are needed before C++17.
+constexpr size_t AcStrategy::kMaxCoeffBlocks;
+constexpr size_t AcStrategy::kMaxBlockDim;
+constexpr size_t AcStrategy::kMaxCoeffArea;
+
+AcStrategyImage::AcStrategyImage(size_t xsize, size_t ysize)
+    : layers_(xsize, ysize) {
+  row_ = layers_.Row(0);
+  stride_ = layers_.PixelsPerRow();
+}
+
+size_t AcStrategyImage::CountBlocks(AcStrategy::Type type) const {
+  size_t ret = 0;
+  for (size_t y = 0; y < layers_.ysize(); y++) {
+    const uint8_t* JXL_RESTRICT row = layers_.ConstRow(y);
+    for (size_t x = 0; x < layers_.xsize(); x++) {
+      if (row[x] == ((static_cast<uint8_t>(type) << 1) | 1)) ret++;
+    }
+  }
+  return ret;
+}
+
+}  // namespace jxl