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/encoder/generic_encoder.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/bitwriter.h"
+#include "av1/common/generic_code.h"
+#include "av1/common/odintrin.h"
+#include "pvq_encoder.h"
+
+/** Encodes a value from 0 to N-1 (with N up to 16) based on a cdf and adapts
+ * the cdf accordingly.
+ *
+ * @param [in,out] w     multi-symbol entropy encoder
+ * @param [in]     val   variable being encoded
+ * @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)
+ */
+void aom_encode_cdf_adapt_q15(aom_writer *w, int val, uint16_t *cdf, int n,
+ int *count, int rate) {
+  int i;
+  if (*count == 0) {
+    /* On the first call, we normalize the cdf to (32768 - n). This should
+       eventually be moved to the state init, but for now it makes it much
+       easier to experiment and convert symbols to the Q15 adaptation.*/
+    int ft;
+    ft = cdf[n - 1];
+    for (i = 0; i < n; i++) {
+      cdf[i] = AOM_ICDF(cdf[i]*32768/ft);
+    }
+  }
+  aom_write_cdf(w, val, cdf, n);
+  aom_cdf_adapt_q15(val, cdf, n, count, rate);
+}
+
+/** 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] w     multi-symbol entropy encoder
+ * @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)
+ */
+void generic_encode(aom_writer *w, generic_encoder *model, int x,
+ int *ex_q16, int integration) {
+  int lg_q1;
+  int shift;
+  int id;
+  uint16_t *cdf;
+  int xs;
+  lg_q1 = log_ex(*ex_q16);
+  OD_LOG((OD_LOG_ENTROPY_CODER, OD_LOG_DEBUG,
+   "%d %d", *ex_q16, lg_q1));
+  /* 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 = (x + (1 << shift >> 1)) >> shift;
+  aom_write_symbol_pvq(w, OD_MINI(15, xs), cdf, 16);
+  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)));
+    /* Encode the tail of the distribution assuming exponential decay. */
+    aom_laplace_encode_special(w, xs - 15, decay);
+  }
+  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) {
+      aom_write_literal(w, x - (xs << shift) + (!special << (shift - 1)),
+       shift - special);
+    }
+  }
+  generic_model_update(ex_q16, x, integration);
+  OD_LOG((OD_LOG_ENTROPY_CODER, OD_LOG_DEBUG,
+   "enc: %d %d %d %d %d %x", *ex_q16, x, shift, id, xs, enc->rng));
+}
+
+/** Estimates the cost of encoding a value with generic_encode().
+ *
+ * @param [in,out] model generic probability model
+ * @param [in]     x     variable being encoded
+ * @param [in,out] ExQ16 expectation of x (adapted)
+ * @return number of bits (approximation)
+ */
+double generic_encode_cost(generic_encoder *model, int x, int *ex_q16) {
+  int lg_q1;
+  int shift;
+  int id;
+  uint16_t *cdf;
+  int xs;
+  int extra;
+  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 = (x + (1 << shift >> 1)) >> shift;
+  extra = 0;
+  if (shift) extra = shift - (xs == 0);
+  xs = OD_MINI(15, xs);
+  /* Shortcut: assume it's going to cost 2 bits for the Laplace coder. */
+  if (xs == 15) extra += 2;
+  return
+      extra - OD_LOG2((double)(cdf[xs] - (xs == 0 ? 0 : cdf[xs - 1]))/cdf[15]);
+}
+
+/*Estimates the cost of encoding a value with a given CDF.*/
+double od_encode_cdf_cost(int val, uint16_t *cdf, int n) {
+  int total_prob;
+  int prev_prob;
+  double val_prob;
+  OD_ASSERT(n > 0);
+  total_prob = cdf[n - 1];
+  if (val == 0) {
+    prev_prob = 0;
+  }
+  else {
+    prev_prob = cdf[val - 1];
+  }
+  val_prob = (cdf[val] - prev_prob) / (double)total_prob;
+  return -OD_LOG2(val_prob);
+}