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diff --git a/third_party/jpeg-xl/lib/jxl/entropy_coder.h b/third_party/jpeg-xl/lib/jxl/entropy_coder.h
new file mode 100644
index 0000000000..e4afa7a631
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+++ b/third_party/jpeg-xl/lib/jxl/entropy_coder.h
@@ -0,0 +1,45 @@
+// 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_ENTROPY_CODER_H_
+#define LIB_JXL_ENTROPY_CODER_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "lib/jxl/ac_context.h"
+#include "lib/jxl/base/compiler_specific.h"
+#include "lib/jxl/dec_bit_reader.h"
+#include "lib/jxl/field_encodings.h"
+
+// Entropy coding and context modeling of DC and AC coefficients, as well as AC
+// strategy and quantization field.
+
+namespace jxl {
+
+static JXL_INLINE int32_t PredictFromTopAndLeft(
+    const int32_t* const JXL_RESTRICT row_top,
+    const int32_t* const JXL_RESTRICT row, size_t x, int32_t default_val) {
+  if (x == 0) {
+    return row_top == nullptr ? default_val : row_top[x];
+  }
+  if (row_top == nullptr) {
+    return row[x - 1];
+  }
+  return (row_top[x] + row[x - 1] + 1) / 2;
+}
+
+static constexpr U32Enc kDCThresholdDist(Bits(4), BitsOffset(8, 16),
+                                         BitsOffset(16, 272),
+                                         BitsOffset(32, 65808));
+
+static constexpr U32Enc kQFThresholdDist(Bits(2), BitsOffset(3, 4),
+                                         BitsOffset(5, 12), BitsOffset(8, 44));
+
+Status DecodeBlockCtxMap(BitReader* br, BlockCtxMap* block_ctx_map);
+
+}  // namespace jxl
+
+#endif  // LIB_JXL_ENTROPY_CODER_H_