core/lib/me.c

   1 /*
   2  * Copyright (c) 2005, Swedish Institute of Computer Science
   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
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. Neither the name of the Institute nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  *
  29  * This file is part of the Contiki operating system.
  30  *
  31  * @(#)$Id: me.c,v 1.1 2006/06/17 22:41:18 adamdunkels Exp $
  32  */
  33
  34 /** \addtogroup me
  35  * @{ */
  36
  37 /**
  38  * \file
  39  * Implementation of the table-driven Manchester encoding and decoding.
  40  * \author
  41  * Adam Dunkels <adam@sics.se>
  42  */
  43
  44 #include "me_tabs.h"
  45
  46 /*---------------------------------------------------------------------------*/
  47 /**
  48  * Manchester encode an 8-bit byte.
  49  *
  50  * This function Manchester encodes an 8-bit byte into a 16-bit
  51  * word. The function me_decode() does the inverse operation.
  52  *
  53  * \param c The byte to be encoded
  54  *
  55  * \retval The encoded word.
  56  */
  57 /*---------------------------------------------------------------------------*/
  58 unsigned short
  59 me_encode(unsigned char c)
  60 {
  61   return me_encode_tab[c];
  62 }
  63 /*---------------------------------------------------------------------------*/
  64 /**
  65  * Decode a Manchester encoded 16-bit word.
  66  *
  67  * This function decodes a Manchester encoded 16-bit word into a 8-bit
  68  * byte. The function does not check for parity errors in the encoded
  69  * byte.
  70  *
  71  * \param m The 16-bit Manchester encoded word
  72  * \return The decoded 8-bit byte
  73  */
  74 /*---------------------------------------------------------------------------*/
  75 unsigned char
  76 me_decode16(unsigned short m)
  77 {
  78   unsigned char m1, m2, c;
  79
  80   m1 = m >> 8;
  81   m2 = m & 0xff;
  82
  83   c = (me_decode_tab[m1] << 4) |
  84     me_decode_tab[m2];
  85   return c;
  86 }
  87 /*---------------------------------------------------------------------------*/
  88 /**
  89  * Decode a Manchester encoded 8-bit byte.
  90  *
  91  * This function decodes a Manchester encoded 8-bit byte into 4
  92  * decoded bits.. The function does not check for parity errors in the
  93  * encoded byte.
  94  *
  95  * \param m The 8-bit Manchester encoded byte
  96  * \return The decoded 4 bits
  97  */
  98 /*---------------------------------------------------------------------------*/
  99 unsigned char
 100 me_decode8(unsigned char m)
 101 {
 102   return  me_decode_tab[m];
 103 }
 104 /*---------------------------------------------------------------------------*/
 105 /**
 106  * Check if an encoded byte is valid.
 107  */
 108 /*---------------------------------------------------------------------------*/
 109 unsigned char
 110 me_valid(unsigned char m)
 111 {
 112   return me_valid_tab[m];
 113 }
 114 /*---------------------------------------------------------------------------*/
 115
 116 /** @} */
 117