1 files changed, 42 insertions, 0 deletions
diff --git a/src/common/reverse.c b/src/common/reverse.c
new file mode 100644
index 000000000..f65540d54
--- /dev/null
+++ b/src/common/reverse.c
@@ -0,0 +1,42 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2004-2006 Sage Weil <sage@newdream.net>
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software 
+ * Foundation.  See file COPYING.
+ * 
+ */
+
+#include "reverse.h"
+
+uint32_t reverse_bits(uint32_t v) {
+  if (v == 0)
+    return v;
+
+  /* reverse bits
+   * swap odd and even bits
+   */
+  v = ((v >> 1) & 0x55555555) | ((v & 0x55555555) << 1);
+  /* swap consecutive pairs */
+  v = ((v >> 2) & 0x33333333) | ((v & 0x33333333) << 2);
+  /* swap nibbles ... */
+  v = ((v >> 4) & 0x0F0F0F0F) | ((v & 0x0F0F0F0F) << 4);
+  /* swap bytes */
+  v = ((v >> 8) & 0x00FF00FF) | ((v & 0x00FF00FF) << 8);
+  /* swap 2-byte long pairs */
+  v = ( v >> 16             ) | ( v               << 16);                                
+  return v;
+}
+
+uint32_t reverse_nibbles(uint32_t retval) {
+  /* reverse nibbles */
+  retval = ((retval & 0x0f0f0f0f) << 4) | ((retval & 0xf0f0f0f0) >> 4);
+  retval = ((retval & 0x00ff00ff) << 8) | ((retval & 0xff00ff00) >> 8);
+  retval = ((retval & 0x0000ffff) << 16) | ((retval & 0xffff0000) >> 16);
+  return retval;
+}