libvpx: Add VP9 decoder.

source/libvpx/vp9/decoder/vp9_dboolhuff.h

+/*
+ *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+
+#ifndef VP9_DECODER_VP9_DBOOLHUFF_H_
+#define VP9_DECODER_VP9_DBOOLHUFF_H_
+#include <stddef.h>
+#include <limits.h>
+#include "vpx_ports/config.h"
+#include "vpx_ports/mem.h"
+#include "vpx/vpx_integer.h"
+
+typedef size_t VP9_BD_VALUE;
+
+# define VP9_BD_VALUE_SIZE ((int)sizeof(VP9_BD_VALUE)*CHAR_BIT)
+/*This is meant to be a large, positive constant that can still be efficiently
+   loaded as an immediate (on platforms like ARM, for example).
+  Even relatively modest values like 100 would work fine.*/
+# define VP9_LOTS_OF_BITS (0x40000000)
+
+typedef struct {
+  const unsigned char *user_buffer_end;
+  const unsigned char *user_buffer;
+  VP9_BD_VALUE         value;
+  int                  count;
+  unsigned int         range;
+} BOOL_DECODER;
+
+DECLARE_ALIGNED(16, extern const unsigned char, vp9_norm[256]);
+
+int vp9_start_decode(BOOL_DECODER *br,
+                     const unsigned char *source,
+                     unsigned int source_sz);
+
+void vp9_bool_decoder_fill(BOOL_DECODER *br);
+
+int vp9_decode_uniform(BOOL_DECODER *br, int n);
+int vp9_decode_term_subexp(BOOL_DECODER *br, int k, int num_syms);
+int vp9_inv_recenter_nonneg(int v, int m);
+
+/*The refill loop is used in several places, so define it in a macro to make
+   sure they're all consistent.
+  An inline function would be cleaner, but has a significant penalty, because
+   multiple BOOL_DECODER fields must be modified, and the compiler is not smart
+   enough to eliminate the stores to those fields and the subsequent reloads
+   from them when inlining the function.*/
+#define VP9DX_BOOL_DECODER_FILL(_count,_value,_bufptr,_bufend) \
+  do \
+  { \
+    int shift = VP9_BD_VALUE_SIZE - 8 - ((_count) + 8); \
+    int loop_end, x; \
+    int bits_left = (int)(((_bufend)-(_bufptr))*CHAR_BIT); \
+    \
+    x = shift + CHAR_BIT - bits_left; \
+    loop_end = 0; \
+    if(x >= 0) \
+    { \
+      (_count) += VP9_LOTS_OF_BITS; \
+      loop_end = x; \
+      if(!bits_left) break; \
+    } \
+    while(shift >= loop_end) \
+    { \
+      (_count) += CHAR_BIT; \
+      (_value) |= (VP9_BD_VALUE)*(_bufptr)++ << shift; \
+      shift -= CHAR_BIT; \
+    } \
+  } \
+  while(0) \
+
+
+static int decode_bool(BOOL_DECODER *br, int probability) {
+  unsigned int bit = 0;
+  VP9_BD_VALUE value;
+  unsigned int split;
+  VP9_BD_VALUE bigsplit;
+  int count;
+  unsigned int range;
+
+  split = 1 + (((br->range - 1) * probability) >> 8);
+
+  if (br->count < 0)
+    vp9_bool_decoder_fill(br);
+
+  value = br->value;
+  count = br->count;
+
+  bigsplit = (VP9_BD_VALUE)split << (VP9_BD_VALUE_SIZE - 8);
+
+  range = split;
+
+  if (value >= bigsplit) {
+    range = br->range - split;
+    value = value - bigsplit;
+    bit = 1;
+  }
+
+  {
+    register unsigned int shift = vp9_norm[range];
+    range <<= shift;
+    value <<= shift;
+    count -= shift;
+  }
+  br->value = value;
+  br->count = count;
+  br->range = range;
+
+  return bit;
+}
+
+static int decode_value(BOOL_DECODER *br, int bits) {
+  int z = 0;
+  int bit;
+
+  for (bit = bits - 1; bit >= 0; bit--) {
+    z |= (decode_bool(br, 0x80) << bit);
+  }
+
+  return z;
+}
+
+static int bool_error(BOOL_DECODER *br) {
+  /* Check if we have reached the end of the buffer.
+   *
+   * Variable 'count' stores the number of bits in the 'value' buffer, minus
+   * 8. The top byte is part of the algorithm, and the remainder is buffered
+   * to be shifted into it. So if count == 8, the top 16 bits of 'value' are
+   * occupied, 8 for the algorithm and 8 in the buffer.
+   *
+   * When reading a byte from the user's buffer, count is filled with 8 and
+   * one byte is filled into the value buffer. When we reach the end of the
+   * data, count is additionally filled with VP9_LOTS_OF_BITS. So when
+   * count == VP9_LOTS_OF_BITS - 1, the user's data has been exhausted.
+   */
+  if ((br->count > VP9_BD_VALUE_SIZE) && (br->count < VP9_LOTS_OF_BITS)) {
+    /* We have tried to decode bits after the end of
+     * stream was encountered.
+     */
+    return 1;
+  }
+
+  /* No error. */
+  return 0;
+}
+
+extern int vp9_decode_unsigned_max(BOOL_DECODER *br, int max);
+
+#endif