avr-libc  2.0.0 Standard C library for AVR-GCC
parity.h
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1 /* Copyright (c) 2002, Marek Michalkiewicz
2  Copyright (c) 2004,2005,2007 Joerg Wunsch
4
5  Redistribution and use in source and binary forms, with or without
6  modification, are permitted provided that the following conditions are met:
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8  * Redistributions of source code must retain the above copyright
9  notice, this list of conditions and the following disclaimer.
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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
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16  * Neither the name of the copyright holders nor the names of
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18  from this software without specific prior written permission.
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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
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23  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
24  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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30  POSSIBILITY OF SUCH DAMAGE. */
31
32 /* $Id: parity_8h_source.html,v 1.1.1.6 2016/02/09 07:13:44 joerg_wunsch Exp$ */
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_ */