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parity.h
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1 /* Copyright (c) 2002, Marek Michalkiewicz
2 Copyright (c) 2004,2005,2007 Joerg Wunsch
3 All rights reserved.
4
5 Redistribution and use in source and binary forms, with or without
6 modification, are permitted provided that the following conditions are met:
7
8 * Redistributions of source code must retain the above copyright
9 notice, this list of conditions and the following disclaimer.
10
11 * Redistributions in binary form must reproduce the above copyright
12 notice, this list of conditions and the following disclaimer in
13 the documentation and/or other materials provided with the
14 distribution.
15
16 * Neither the name of the copyright holders nor the names of
17 contributors may be used to endorse or promote products derived
18 from this software without specific prior written permission.
19
20 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
21 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
24 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
25 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
26 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
27 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
28 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
29 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
30 POSSIBILITY OF SUCH DAMAGE. */
31
32 /* $Id: parity.h 1196 2007-01-23 15:34:58Z joerg_wunsch $ */
33
34 #ifndef _UTIL_PARITY_H_
35 #define _UTIL_PARITY_H_
36
37 /** \file */
38 /** \defgroup util_parity <util/parity.h>: Parity bit generation
39 \code #include <util/parity.h> \endcode
40
41 This header file contains optimized assembler code to calculate
42 the parity bit for a byte.
43 */
44 /** \def parity_even_bit
45 \ingroup util_parity
46 \returns 1 if \c val has an odd number of bits set. */
47 #define parity_even_bit(val) \
48 (__extension__({ \
49 unsigned char __t; \
50 __asm__ ( \
51 "mov __tmp_reg__,%0" "\n\t" \
52 "swap %0" "\n\t" \
53 "eor %0,__tmp_reg__" "\n\t" \
54 "mov __tmp_reg__,%0" "\n\t" \
55 "lsr %0" "\n\t" \
56 "lsr %0" "\n\t" \
57 "eor %0,__tmp_reg__" \
58 : "=r" (__t) \
59 : "0" ((unsigned char)(val)) \
60 : "r0" \
61 ); \
62 (((__t + 1) >> 1) & 1); \
63 }))
64
65 #endif /* _UTIL_PARITY_H_ */

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