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diff --git a/third_party/jpeg-xl/lib/jxl/enc_ac_strategy.h b/third_party/jpeg-xl/lib/jxl/enc_ac_strategy.h
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+++ b/third_party/jpeg-xl/lib/jxl/enc_ac_strategy.h
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+// 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.
+
+#ifndef LIB_JXL_ENC_AC_STRATEGY_H_
+#define LIB_JXL_ENC_AC_STRATEGY_H_
+
+#include <stdint.h>
+
+#include "lib/jxl/ac_strategy.h"
+#include "lib/jxl/base/data_parallel.h"
+#include "lib/jxl/base/status.h"
+#include "lib/jxl/common.h"
+#include "lib/jxl/dec_ans.h"
+#include "lib/jxl/enc_cache.h"
+#include "lib/jxl/enc_params.h"
+#include "lib/jxl/image.h"
+#include "lib/jxl/quant_weights.h"
+
+// `FindBestAcStrategy` uses heuristics to choose which AC strategy should be
+// used in each block, as well as the initial quantization field.
+
+namespace jxl {
+
+struct AuxOut;
+
+// AC strategy selection: utility struct.
+
+struct ACSConfig {
+  const DequantMatrices* JXL_RESTRICT dequant;
+  float info_loss_multiplier;
+  float info_loss_multiplier2;
+  float* JXL_RESTRICT quant_field_row;
+  size_t quant_field_stride;
+  float* JXL_RESTRICT masking_field_row;
+  size_t masking_field_stride;
+  const float* JXL_RESTRICT src_rows[3];
+  size_t src_stride;
+  // Cost for 1 (-1), 2 (-2) explicitly, cost for others computed with cost1 +
+  // cost2 + sqrt(q) * cost_delta.
+  float cost1;
+  float cost2;
+  float cost_delta;
+  float base_entropy;
+  float zeros_mul;
+  const float& Pixel(size_t c, size_t x, size_t y) const {
+    return src_rows[c][y * src_stride + x];
+  }
+  float Masking(size_t bx, size_t by) const {
+    JXL_DASSERT(masking_field_row[by * masking_field_stride + bx] > 0);
+    return masking_field_row[by * masking_field_stride + bx];
+  }
+  float Quant(size_t bx, size_t by) const {
+    JXL_DASSERT(quant_field_row[by * quant_field_stride + bx] > 0);
+    return quant_field_row[by * quant_field_stride + bx];
+  }
+};
+
+struct AcStrategyHeuristics {
+  void Init(const Image3F& src, PassesEncoderState* enc_state);
+  void ProcessRect(const Rect& rect);
+  void Finalize(AuxOut* aux_out);
+  ACSConfig config;
+  PassesEncoderState* enc_state;
+};
+
+// Debug.
+void DumpAcStrategy(const AcStrategyImage& ac_strategy, size_t xsize,
+                    size_t ysize, const char* tag, AuxOut* aux_out);
+
+}  // namespace jxl
+
+#endif  // LIB_JXL_ENC_AC_STRATEGY_H_