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/av1/decoder/generic_decoder.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.
+ */
+
+/* clang-format off */
+
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <stdio.h>
+
+#include "aom_dsp/bitreader.h"
+#include "av1/common/generic_code.h"
+#include "av1/common/odintrin.h"
+#include "pvq_decoder.h"
+
+/** Decodes a value from 0 to N-1 (with N up to 16) based on a cdf and adapts
+ * the cdf accordingly.
+ *
+ * @param [in,out] r     multi-symbol entropy decoder
+ * @param [in,out] cdf   CDF of the variable (Q15)
+ * @param [in]     n     number of values possible
+ * @param [in,out] count number of symbols encoded with that cdf so far
+ * @param [in]     rate  adaptation rate shift (smaller is faster)
+ * @return decoded variable
+ */
+int aom_decode_cdf_adapt_q15_(aom_reader *r, uint16_t *cdf, int n,
+ int *count, int rate ACCT_STR_PARAM) {
+  int val;
+  int i;
+  if (*count == 0) {
+    int ft;
+    ft = cdf[n - 1];
+    for (i = 0; i < n; i++) {
+      cdf[i] = AOM_ICDF(cdf[i]*32768/ft);
+    }
+  }
+  val = aom_read_cdf(r, cdf, n, ACCT_STR_NAME);
+  aom_cdf_adapt_q15(val, cdf, n, count, rate);
+  return val;
+}
+
+/** Encodes a random variable using a "generic" model, assuming that the
+ * distribution is one-sided (zero and up), has a single mode, and decays
+ * exponentially past the model.
+ *
+ * @param [in,out] r     multi-symbol entropy decoder
+ * @param [in,out] model generic probability model
+ * @param [in]     x     variable being encoded
+ * @param [in,out] ExQ16 expectation of x (adapted)
+ * @param [in]     integration integration period of ExQ16 (leaky average over
+ * 1<<integration samples)
+ *
+ * @retval decoded variable x
+ */
+int generic_decode_(aom_reader *r, generic_encoder *model,
+ int *ex_q16, int integration ACCT_STR_PARAM) {
+  int lg_q1;
+  int shift;
+  int id;
+  uint16_t *cdf;
+  int xs;
+  int lsb;
+  int x;
+  lsb = 0;
+  lg_q1 = log_ex(*ex_q16);
+  /* If expectation is too large, shift x to ensure that
+     all we have past xs=15 is the exponentially decaying tail
+     of the distribution. */
+  shift = OD_MAXI(0, (lg_q1 - 5) >> 1);
+  /* Choose the cdf to use: we have two per "octave" of ExQ16. */
+  id = OD_MINI(GENERIC_TABLES - 1, lg_q1);
+  cdf = model->cdf[id];
+  xs = aom_read_symbol_pvq(r, cdf, 16, ACCT_STR_NAME);
+  if (xs == 15) {
+    int e;
+    unsigned decay;
+    /* Estimate decay based on the assumption that the distribution is close
+       to Laplacian for large values. We should probably have an adaptive
+       estimate instead. Note: The 2* is a kludge that's not fully understood
+       yet. */
+    OD_ASSERT(*ex_q16 < INT_MAX >> 1);
+    e = ((2**ex_q16 >> 8) + (1 << shift >> 1)) >> shift;
+    decay = OD_MAXI(2, OD_MINI(254, 256*e/(e + 256)));
+    xs += aom_laplace_decode_special(r, decay, ACCT_STR_NAME);
+  }
+  if (shift != 0) {
+    int special;
+    /* Because of the rounding, there's only half the number of possibilities
+       for xs=0 */
+    special = xs == 0;
+    if (shift - special > 0) {
+      lsb = aom_read_literal(r, shift - special, ACCT_STR_NAME);
+    }
+    lsb -= !special << (shift - 1);
+  }
+  x = (xs << shift) + lsb;
+  generic_model_update(ex_q16, x, integration);
+  OD_LOG((OD_LOG_ENTROPY_CODER, OD_LOG_DEBUG,
+   "dec: %d %d %d %d %d %x", *ex_q16, x, shift, id, xs, dec->rng));
+  return x;
+}