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234 lines
4.9 KiB
C
234 lines
4.9 KiB
C
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/*
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* libzvbi -- Error correction functions
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*
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* Copyright (C) 2001, 2002, 2003, 2004, 2007 Michael H. Schimek
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Library General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Library General Public License for more details.
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*
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* You should have received a copy of the GNU Library General Public
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* License along with this library; if not, write to the
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* Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
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* Boston, MA 02110-1301 USA.
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*/
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/* $Id: hamm.h,v 1.16 2013-07-10 11:37:13 mschimek Exp $ */
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#ifndef __ZVBI_HAMM_H__
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#define __ZVBI_HAMM_H__
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#include <inttypes.h> /* uintN_t */
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#include "macros.h"
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VBI_BEGIN_DECLS
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/* Public */
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extern const uint8_t _vbi_bit_reverse [256];
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extern const uint8_t _vbi_hamm8_fwd [16];
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extern const int8_t _vbi_hamm8_inv [256];
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extern const int8_t _vbi_hamm24_inv_par [3][256];
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/**
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* @addtogroup Error Error correction functions
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* @ingroup Raw
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* @brief Helper functions to decode sliced VBI data.
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* @{
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*/
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/**
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* @param c Unsigned byte.
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*
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* Reverses the bits of the argument.
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*
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* @returns
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* Data bits 0 [msb] ... 7 [lsb].
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*
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* @since 0.2.12
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*/
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_vbi_inline unsigned int
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vbi_rev8 (unsigned int c)
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{
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return _vbi_bit_reverse[(uint8_t) c];
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}
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/**
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* @param c Unsigned 16 bit word.
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*
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* Reverses (or "reflects") the bits of the argument.
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*
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* @returns
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* Data bits 0 [msb] ... 15 [lsb].
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*
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* @since 0.2.12
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*/
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_vbi_inline unsigned int
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vbi_rev16 (unsigned int c)
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{
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return _vbi_bit_reverse[(uint8_t) c] * 256
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+ _vbi_bit_reverse[(uint8_t)(c >> 8)];
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}
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/**
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* @param p Pointer to a 16 bit word, last significant
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* byte first.
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*
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* Reverses (or "reflects") the bits of the argument.
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*
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* @returns
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* Data bits 0 [msb] ... 15 [lsb].
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*
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* @since 0.2.12
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*/
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_vbi_inline unsigned int
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vbi_rev16p (const uint8_t * p)
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{
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return _vbi_bit_reverse[p[0]] * 256
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+ _vbi_bit_reverse[p[1]];
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}
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/**
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* @param c Unsigned byte.
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*
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* @returns
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* Changes the most significant bit of the byte
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* to make the number of set bits odd.
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*
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* @since 0.2.12
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*/
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_vbi_inline unsigned int
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vbi_par8 (unsigned int c)
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{
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c &= 255;
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/* if 0 == (inv_par[] & 32) change bit 7 of c. */
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c ^= 128 & ~(_vbi_hamm24_inv_par[0][c] << 2);
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return c;
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}
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/**
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* @param c Unsigned byte.
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*
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* @returns
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* If the byte has odd parity (sum of bits modulo 2 is 1) the
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* byte AND 127, otherwise a negative value.
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*
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* @since 0.2.12
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*/
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_vbi_inline int
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vbi_unpar8 (unsigned int c)
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{
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/* Disabled until someone finds a reliable way
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to test for cmov support at compile time. */
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#if 0
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int r = c & 127;
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/* This saves cache flushes and an explicit branch. */
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__asm__ (" testb %1,%1\n"
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" cmovp %2,%0\n"
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: "+&a" (r) : "c" (c), "rm" (-1));
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return r;
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#endif
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if (_vbi_hamm24_inv_par[0][(uint8_t) c] & 32) {
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return c & 127;
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} else {
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/* The idea is to OR results together to find a parity
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error in a sequence, rather than a test and branch on
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each byte. */
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return -1;
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}
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}
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extern void
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vbi_par (uint8_t * p,
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unsigned int n);
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extern int
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vbi_unpar (uint8_t * p,
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unsigned int n);
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/**
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* @param c Integer between 0 ... 15.
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*
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* Encodes a nibble with Hamming 8/4 protection
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* as specified in EN 300 706, Section 8.2.
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*
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* @returns
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* Hamming encoded unsigned byte, lsb first transmitted.
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*
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* @since 0.2.12
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*/
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_vbi_inline unsigned int
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vbi_ham8 (unsigned int c)
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{
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return _vbi_hamm8_fwd[c & 15];
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}
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/**
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* @param c Hamming 8/4 protected byte, lsb first transmitted.
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*
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* Decodes a Hamming 8/4 protected byte
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* as specified in EN 300 706, Section 8.2.
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*
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* @returns
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* Data bits (D4 [msb] ... D1 [lsb]) or a negative
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* value if the byte contained uncorrectable errors.
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*
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* @since 0.2.12
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*/
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_vbi_inline int
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vbi_unham8 (unsigned int c)
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{
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return _vbi_hamm8_inv[(uint8_t) c];
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}
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/**
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* @param p Pointer to a Hamming 8/4 protected 16 bit word,
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* last significant byte first, lsb first transmitted.
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*
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* Decodes a Hamming 8/4 protected byte pair
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* as specified in EN 300 706, Section 8.2.
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*
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* @returns
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* Data bits D4 [msb] ... D1 of first byte and D4 ... D1 [lsb]
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* of second byte, or a negative value if any of the bytes
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* contained uncorrectable errors.
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*
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* @since 0.2.12
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*/
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_vbi_inline int
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vbi_unham16p (const uint8_t * p)
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{
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return ((int) _vbi_hamm8_inv[p[0]])
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| (((int) _vbi_hamm8_inv[p[1]]) << 4);
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}
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extern void
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vbi_ham24p (uint8_t * p,
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unsigned int c);
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extern int
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vbi_unham24p (const uint8_t * p)
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_vbi_pure;
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/** @} */
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/* Private */
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VBI_END_DECLS
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#endif /* __ZVBI_HAMM_H__ */
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/*
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Local variables:
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c-set-style: K&R
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c-basic-offset: 8
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End:
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*/
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