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 - 1) / CHAR_BIT;
+  return (rb->bit_offset + 7) >> 3;
 }
 
 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) {
+  const size_t p = off >> 3;
+  const int q = 7 - (int)(off & 0x7);
+  if (rb->bit_buffer + p < rb->bit_buffer_end) {
+    const int bit = (rb->bit_buffer[p] >> q) & 1;
+    rb->bit_offset = off + 1;
+    return bit;
+  } else {
     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;
 }