Import aom library

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

The commit used was 4d668d7feb1f8abd809d1bca0418570a7f142a36.

1 files changed, 53 insertions, 0 deletions

diff --git a/third_party/aom/aom_dsp/entcode.c b/third_party/aom/aom_dsp/entcode.c
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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.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "./config.h"
+#endif
+
+#include "aom_dsp/entcode.h"
+
+/*Given the current total integer number of bits used and the current value of
+   rng, computes the fraction number of bits used to OD_BITRES precision.
+  This is used by od_ec_enc_tell_frac() and od_ec_dec_tell_frac().
+  nbits_total: The number of whole bits currently used, i.e., the value
+                returned by od_ec_enc_tell() or od_ec_dec_tell().
+  rng: The current value of rng from either the encoder or decoder state.
+  Return: The number of bits scaled by 2**OD_BITRES.
+          This will always be slightly larger than the exact value (e.g., all
+           rounding error is in the positive direction).*/
+uint32_t od_ec_tell_frac(uint32_t nbits_total, uint32_t rng) {
+  uint32_t nbits;
+  int l;
+  int i;
+  /*To handle the non-integral number of bits still left in the encoder/decoder
+     state, we compute the worst-case number of bits of val that must be
+     encoded to ensure that the value is inside the range for any possible
+     subsequent bits.
+    The computation here is independent of val itself (the decoder does not
+     even track that value), even though the real number of bits used after
+     od_ec_enc_done() may be 1 smaller if rng is a power of two and the
+     corresponding trailing bits of val are all zeros.
+    If we did try to track that special case, then coding a value with a
+     probability of 1/(1 << n) might sometimes appear to use more than n bits.
+    This may help explain the surprising result that a newly initialized
+     encoder or decoder claims to have used 1 bit.*/
+  nbits = nbits_total << OD_BITRES;
+  l = 0;
+  for (i = OD_BITRES; i-- > 0;) {
+    int b;
+    rng = rng * rng >> 15;
+    b = (int)(rng >> 16);
+    l = l << 1 | b;
+    rng >>= b;
+  }
+  return nbits - l;
+}