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/buf_ans.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_DSP_BUF_ANS_H_
+#define AOM_DSP_BUF_ANS_H_
+// Buffered forward ANS writer.
+// Symbols are written to the writer in forward (decode) order and serialized
+// backwards due to ANS's stack like behavior.
+
+#include <assert.h>
+#include "./aom_config.h"
+#include "aom/aom_integer.h"
+#include "aom_dsp/ans.h"
+#include "aom_dsp/answriter.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif  // __cplusplus
+
+#define ANS_METHOD_RABS 0
+#define ANS_METHOD_RANS 1
+
+struct buffered_ans_symbol {
+  unsigned int method : 1;  // one of ANS_METHOD_RABS or ANS_METHOD_RANS
+  // TODO(aconverse): Should be possible to write this in terms of start for ABS
+  unsigned int val_start : RANS_PROB_BITS;  // Boolean value for ABS
+                                            // start in symbol cycle for Rans
+  unsigned int prob : RANS_PROB_BITS;       // Probability of this symbol
+};
+
+struct BufAnsCoder {
+  struct aom_internal_error_info *error;
+  struct buffered_ans_symbol *buf;
+  struct AnsCoder ans;
+  int size;
+  int offset;
+  int output_bytes;
+#if ANS_MAX_SYMBOLS
+  int window_size;
+#endif
+};
+
+// Allocate a buffered ANS coder to store size symbols.
+// When ANS_MAX_SYMBOLS is turned on, the size is the fixed size of each ANS
+// partition.
+// When ANS_MAX_SYMBOLS is turned off, size is merely an initial hint and the
+// buffer will grow on demand
+void aom_buf_ans_alloc(struct BufAnsCoder *c,
+                       struct aom_internal_error_info *error, int hint);
+
+void aom_buf_ans_free(struct BufAnsCoder *c);
+
+#if !ANS_MAX_SYMBOLS
+void aom_buf_ans_grow(struct BufAnsCoder *c);
+#endif
+
+void aom_buf_ans_flush(struct BufAnsCoder *const c);
+
+static INLINE void buf_ans_write_init(struct BufAnsCoder *const c,
+                                      uint8_t *const output_buffer) {
+  c->offset = 0;
+  c->output_bytes = 0;
+  ans_write_init(&c->ans, output_buffer);
+}
+
+static INLINE void buf_rabs_write(struct BufAnsCoder *const c, uint8_t val,
+                                  AnsP8 prob) {
+  assert(c->offset <= c->size);
+#if !ANS_MAX_SYMBOLS
+  if (c->offset == c->size) {
+    aom_buf_ans_grow(c);
+  }
+#endif
+  c->buf[c->offset].method = ANS_METHOD_RABS;
+  c->buf[c->offset].val_start = val;
+  c->buf[c->offset].prob = prob;
+  ++c->offset;
+#if ANS_MAX_SYMBOLS
+  if (c->offset == c->size) aom_buf_ans_flush(c);
+#endif
+}
+
+// Buffer one symbol for encoding using rANS.
+// cum_prob: The cumulative probability before this symbol (the offset of
+// the symbol in the symbol cycle)
+// prob: The probability of this symbol (l_s from the paper)
+// RANS_PRECISION takes the place of m from the paper.
+static INLINE void buf_rans_write(struct BufAnsCoder *const c,
+                                  aom_cdf_prob cum_prob, aom_cdf_prob prob) {
+  assert(c->offset <= c->size);
+#if !ANS_MAX_SYMBOLS
+  if (c->offset == c->size) {
+    aom_buf_ans_grow(c);
+  }
+#endif
+  c->buf[c->offset].method = ANS_METHOD_RANS;
+  c->buf[c->offset].val_start = cum_prob;
+  c->buf[c->offset].prob = prob;
+  ++c->offset;
+#if ANS_MAX_SYMBOLS
+  if (c->offset == c->size) aom_buf_ans_flush(c);
+#endif
+}
+
+static INLINE void buf_rabs_write_bit(struct BufAnsCoder *c, int bit) {
+  buf_rabs_write(c, bit, 128);
+}
+
+static INLINE void buf_rabs_write_literal(struct BufAnsCoder *c, int literal,
+                                          int bits) {
+  int bit;
+
+  assert(bits < 31);
+  for (bit = bits - 1; bit >= 0; bit--)
+    buf_rabs_write_bit(c, 1 & (literal >> bit));
+}
+
+static INLINE int buf_ans_write_end(struct BufAnsCoder *const c) {
+  assert(c->offset == 0);
+  return c->output_bytes;
+}
+#ifdef __cplusplus
+}  // extern "C"
+#endif  // __cplusplus
+#endif  // AOM_DSP_BUF_ANS_H_