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1 | // -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- |
2 | // vim: ts=8 sw=2 smarttab | |
3 | /* | |
4 | * Ceph - scalable distributed file system | |
5 | * | |
6 | * Copyright (C) 2004-2006 Sage Weil <sage@newdream.net> | |
7 | * | |
8 | * This is free software; you can redistribute it and/or | |
9 | * modify it under the terms of the GNU Lesser General Public | |
10 | * License version 2.1, as published by the Free Software | |
11 | * Foundation. See file COPYING. | |
12 | * | |
13 | */ | |
14 | ||
15 | #include "reverse.h" | |
16 | ||
17 | uint32_t reverse_bits(uint32_t v) { | |
18 | if (v == 0) | |
19 | return v; | |
20 | ||
21 | /* reverse bits | |
22 | * swap odd and even bits | |
23 | */ | |
24 | v = ((v >> 1) & 0x55555555) | ((v & 0x55555555) << 1); | |
25 | /* swap consecutive pairs */ | |
26 | v = ((v >> 2) & 0x33333333) | ((v & 0x33333333) << 2); | |
27 | /* swap nibbles ... */ | |
28 | v = ((v >> 4) & 0x0F0F0F0F) | ((v & 0x0F0F0F0F) << 4); | |
29 | /* swap bytes */ | |
30 | v = ((v >> 8) & 0x00FF00FF) | ((v & 0x00FF00FF) << 8); | |
31 | /* swap 2-byte long pairs */ | |
32 | v = ( v >> 16 ) | ( v << 16); | |
33 | return v; | |
34 | } | |
35 | ||
36 | uint32_t reverse_nibbles(uint32_t retval) { | |
37 | /* reverse nibbles */ | |
38 | retval = ((retval & 0x0f0f0f0f) << 4) | ((retval & 0xf0f0f0f0) >> 4); | |
39 | retval = ((retval & 0x00ff00ff) << 8) | ((retval & 0xff00ff00) >> 8); | |
40 | retval = ((retval & 0x0000ffff) << 16) | ((retval & 0xffff0000) >> 16); | |
41 | return retval; | |
42 | } |