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diff --git a/third_party/aom/av1/encoder/cost.h b/third_party/aom/av1/encoder/cost.h
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+++ b/third_party/aom/av1/encoder/cost.h
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+/*
+ * Copyright (c) 2016, Alliance for Open Media. All rights reserved
+ *
+ * This source code is subject to the terms of the BSD 2 Clause License and
+ * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
+ * was not distributed with this source code in the LICENSE file, you can
+ * obtain it at www.aomedia.org/license/software. If the Alliance for Open
+ * Media Patent License 1.0 was not distributed with this source code in the
+ * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
+ */
+
+#ifndef AOM_AV1_ENCODER_COST_H_
+#define AOM_AV1_ENCODER_COST_H_
+
+#include "aom_dsp/prob.h"
+#include "aom/aom_integer.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern const uint16_t av1_prob_cost[128];
+
+// The factor to scale from cost in bits to cost in av1_prob_cost units.
+#define AV1_PROB_COST_SHIFT 9
+
+// Cost of coding an n bit literal, using 128 (i.e. 50%) probability
+// for each bit.
+#define av1_cost_literal(n) ((n) * (1 << AV1_PROB_COST_SHIFT))
+
+// Calculate the cost of a symbol with probability p15 / 2^15
+static INLINE int av1_cost_symbol(aom_cdf_prob p15) {
+  // p15 can be out of range [1, CDF_PROB_TOP - 1]. Clamping it, so that the
+  // following cost calculation works correctly. Otherwise, if p15 =
+  // CDF_PROB_TOP, shift would be -1, and "p15 << shift" would be wrong.
+  p15 = (aom_cdf_prob)clamp(p15, 1, CDF_PROB_TOP - 1);
+  assert(0 < p15 && p15 < CDF_PROB_TOP);
+  const int shift = CDF_PROB_BITS - 1 - get_msb(p15);
+  const int prob = get_prob(p15 << shift, CDF_PROB_TOP);
+  assert(prob >= 128);
+  return av1_prob_cost[prob - 128] + av1_cost_literal(shift);
+}
+
+void av1_cost_tokens_from_cdf(int *costs, const aom_cdf_prob *cdf,
+                              const int *inv_map);
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // AOM_AV1_ENCODER_COST_H_