www.pudn.com > MPEG2systemsrc.rar > IPortFromRam.C

/* Copyright (C) 1995, Tektronix Inc. All Rights Reserved.
 *
 *   Usage Restrictions
 *
 * License is granted to copy, to use, and to make and to use derivative
 * works for research and evaluation purposes only.
 *
 *   Disclaimer of Warranty
 *
 * These software programs are available to the user without any license
 * fee or royalty on an "as is" basis.  Tektronix Inc. disclaims any and
 * all warranties, whether express, implied, or statuary, including any
 * implied warranties or merchantability or of fitness for a particular
 * purpose.  In no event shall the copyright-holder be liable for any 
 * incidental, punitive, or consequential damages of any kind whatsoever
 * arising from the use of these programs.
 *
 * This disclaimer of warranty extends to the user of these programs and
 * user's customers, employees, agents, transferees, successors, and
 * assigns.
 *
 * The Tektronix Inc. does not represent or warrant that the programs
 * furnished hereunder are free of infringement of any third-party
 * patents.
*/

/* IPortFromRam implementation */

#include "IPortFromRam.H"
#include "Utilities.H"

IPortFromRam::IPortFromRam (char* b, int length) : InputPort()
{
  bits = b;
  bits_ptr = 0;
  bits_length = length;
  pos = -1;  // forces read on first call to read_bit
}

char IPortFromRam::input_bit ()
// returns next bit as a char or BADBIT for an error
{
  int result = inc_bit ();
  if (result) return bit2char();
  return BADBIT;
}

char IPortFromRam::input_byte ()
{
  if (pos <= 0)
    {
      byte = bits[bits_ptr];
      bits_ptr++;
      if (bits_ptr >= bits_length) bits_ptr = 0;
    }
  else
    {
      sys_error("can't read_byte; not on byte boundary");
    }
  return byte;
}

int IPortFromRam::inc_bit ()
// increments pos or reads from buffer if necessary
{
  if (pos <= 0)
    {
      byte = bits[bits_ptr];
      bits_ptr++;
      if (bits_ptr >= bits_length) bits_ptr = 0;
      pos = 7;
    }
  else
    {
      pos--;
    }
  return 1;
}

char IPortFromRam::bit2char ()
// returns ONE or ZERO depending on current bit;
{
  return (byte & (1 << pos)) ? ONE : ZERO;
}