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Diffstat (limited to '')
-rw-r--r-- | src/common/reverse.c | 42 |
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; +} |