Import aom library

This is the reference implementation for the Alliance for Open Media's av1 video code.

The commit used was 4d668d7feb1f8abd809d1bca0418570a7f142a36.

third_party/aom/aom_dsp/entcode.h

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+/*
+ * Copyright (c) 2001-2016, 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.
+ */
+
+#if !defined(_entcode_H)
+#define _entcode_H (1)
+#include <limits.h>
+#include <stddef.h>
+#include "av1/common/odintrin.h"
+
+/*OPT: od_ec_window must be at least 32 bits, but if you have fast arithmetic
+   on a larger type, you can speed up the decoder by using it here.*/
+typedef uint32_t od_ec_window;
+
+#define OD_EC_WINDOW_SIZE ((int)sizeof(od_ec_window) * CHAR_BIT)
+
+/*The number of bits to use for the range-coded part of unsigned integers.*/
+#define OD_EC_UINT_BITS (4)
+
+/*The resolution of fractional-precision bit usage measurements, i.e.,
+   3 => 1/8th bits.*/
+#define OD_BITRES (3)
+
+/*With CONFIG_EC_SMALLMUL, the value stored in a CDF is 32768 minus the actual
+   Q15 cumulative probability (an "inverse" CDF).
+  This function converts from one representation to the other (and is its own
+   inverse).*/
+#if CONFIG_EC_SMALLMUL
+#define OD_ICDF(x) (32768U - (x))
+#else
+#define OD_ICDF(x) (x)
+#endif
+
+/*See entcode.c for further documentation.*/
+
+OD_WARN_UNUSED_RESULT uint32_t od_ec_tell_frac(uint32_t nbits_total,
+                                               uint32_t rng);
+
+#endif