libvpx: Add VP9 decoder.

source/libvpx/vp9/decoder/vp9_dboolhuff.c

+/*
+ *  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.
+ */
+
+
+#include "vp9/decoder/vp9_dboolhuff.h"
+#include "vpx_ports/mem.h"
+#include "vpx_mem/vpx_mem.h"
+
+int vp9_start_decode(BOOL_DECODER *br,
+                     const unsigned char *source,
+                     unsigned int source_sz) {
+  br->user_buffer_end = source + source_sz;
+  br->user_buffer     = source;
+  br->value    = 0;
+  br->count    = -8;
+  br->range    = 255;
+
+  if (source_sz && !source)
+    return 1;
+
+  /* Populate the buffer */
+  vp9_bool_decoder_fill(br);
+
+  return 0;
+}
+
+
+void vp9_bool_decoder_fill(BOOL_DECODER *br) {
+  const unsigned char *bufptr;
+  const unsigned char *bufend;
+  VP9_BD_VALUE         value;
+  int                  count;
+  bufend = br->user_buffer_end;
+  bufptr = br->user_buffer;
+  value = br->value;
+  count = br->count;
+
+  VP9DX_BOOL_DECODER_FILL(count, value, bufptr, bufend);
+
+  br->user_buffer = bufptr;
+  br->value = value;
+  br->count = count;
+}
+
+
+static int get_unsigned_bits(unsigned num_values) {
+  int cat = 0;
+  if ((num_values--) <= 1) return 0;
+  while (num_values > 0) {
+    cat++;
+    num_values >>= 1;
+  }
+  return cat;
+}
+
+int vp9_inv_recenter_nonneg(int v, int m) {
+  if (v > (m << 1)) return v;
+  else if ((v & 1) == 0) return (v >> 1) + m;
+  else return m - ((v + 1) >> 1);
+}
+
+int vp9_decode_uniform(BOOL_DECODER *br, int n) {
+  int v;
+  int l = get_unsigned_bits(n);
+  int m = (1 << l) - n;
+  if (!l) return 0;
+  v = decode_value(br, l - 1);
+  if (v < m)
+    return v;
+  else
+    return (v << 1) - m + decode_value(br, 1);
+}
+
+int vp9_decode_term_subexp(BOOL_DECODER *br, int k, int num_syms) {
+  int i = 0, mk = 0, word;
+  while (1) {
+    int b = (i ? k + i - 1 : k);
+    int a = (1 << b);
+    if (num_syms <= mk + 3 * a) {
+      word = vp9_decode_uniform(br, num_syms - mk) + mk;
+      break;
+    } else {
+      if (decode_value(br, 1)) {
+        i++;
+        mk += a;
+      } else {
+        word = decode_value(br, b) + mk;
+        break;
+      }
+    }
+  }
+  return word;
+}
+
+int vp9_decode_unsigned_max(BOOL_DECODER *br, int max) {
+  int data = 0, bit = 0, lmax = max;
+
+  while (lmax) {
+    data |= decode_bool(br, 128) << bit++;
+    lmax >>= 1;
+  }
+  if (data > max)
+    return max;
+  return data;
+}