libvpx: Pull from upstream

source/libvpx/vp9/decoder/vp9_read_bit_buffer.c

+/*
+ *  Copyright (c) 2013 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_read_bit_buffer.h"
+
+size_t vp9_rb_bytes_read(struct vp9_read_bit_buffer *rb) {
+  return rb->bit_offset / CHAR_BIT + (rb->bit_offset % CHAR_BIT > 0);
+}
+
+int vp9_rb_read_bit(struct vp9_read_bit_buffer *rb) {
+  const size_t off = rb->bit_offset;
+  const size_t p = off / CHAR_BIT;
+  const int q = CHAR_BIT - 1 - (int)off % CHAR_BIT;
+  if (rb->bit_buffer + p >= rb->bit_buffer_end) {
+    rb->error_handler(rb->error_handler_data);
+    return 0;
+  } else {
+    const int bit = (rb->bit_buffer[p] & (1 << q)) >> q;
+    rb->bit_offset = off + 1;
+    return bit;
+  }
+}
+
+int vp9_rb_read_literal(struct vp9_read_bit_buffer *rb, int bits) {
+  int value = 0, bit;
+  for (bit = bits - 1; bit >= 0; bit--)
+    value |= vp9_rb_read_bit(rb) << bit;
+  return value;
+}
+
+int vp9_rb_read_signed_literal(struct vp9_read_bit_buffer *rb,
+                               int bits) {
+  const int value = vp9_rb_read_literal(rb, bits);
+  return vp9_rb_read_bit(rb) ? -value : value;
+}