decode()

intT GSE2::waveform::CM6::decode

(

std::istream &

is

)

CM6 subformat decoding function.

The function decodes an integer value from CM6 subformat. It takes an input stream to read from. This is necessary since the function has to skip line-ends on its own. If you want to read from a character string, use string streams. The numerical value returned is just the next decoded integer value from the stream. It is a second difference value. You still have to remove second differences afterwards.

Author

Thomas Forbriger, Stefan Stange and others (see comments in the source code)

Parameters

is	input stream to read from

Returns

next integer value decoded from stream.

See also

GSE2::waveform::TDAT2readCM6

Definition at line 191 of file gsexx_cm6.cc.

Referenced by GSE2::waveform::TDAT2readCM6::convert().

{
// The original version of the core of this function was coded by Stefan
// Stange. The code (decomp_6b) can be found in gse_functions.c in his
// library. Here is the original comment by Stefan Stange:

/*********************************************************************
* Function: decomp_6b
*   This routine evolves the data series from the 6Byte encoding according
*   GSE2.0 based on dcomp6.f in CODECO by Urs Kradolfer. 
*   Input is the character representation (meaning the file pointer to it),
*   the number of samples to be expected and the pointer to the data.
*   Output is the data series in LONG (has to be allocated elsewhere!). 
*   The GSE file must be opened and positioned to or before the "DAT2" line.
*   Returns actual # of samples or -1 as error code.
*   Calls no other routines.
*   St. Stange, 1.10.1998  , verified for PC-byte-sex 11.4.2001
*********************************************************************/
  static int ichar[]={0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
             0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,2,3,4,5,6,7,
             8,9,10,11,0,0,0,0,0,0,0,12,13,14,15,16,17,18,19,20,21,22,
             23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,0,0,0,0,0,0,
             38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,
             57,58,59,60,61,62,63,0,0,0,0,0,0},/*1 more than in FORTRAN*/
             isign=020, ioflow=040, mask1=017, mask2=037, m127=0177;

  int k, inn, jsign=0, joflow=0;
  char inchar;    // character just read from stream
  intT retval;    // decoded samples

  // read next
  is.get(inchar);
  while (inchar == '\n') { is.get(inchar); }
  if (isspace(inchar))
    throw Terror("ERROR (CM6::decode): illegal whitespace");
  if (is.eof())
    throw Terror("ERROR (CM6::decode): illegal end of file");
                                
  /* get ascii code of input character, strip off any higher bits
  (don't know whether it does what it says) and get number representation */
  
  k = int(int(inchar) & m127); 
  inn = ichar[k];
  
  jsign = (inn & isign);            /* get sign bit */
  joflow = (inn & ioflow);          /* get continuation bit if any */
  retval = (long)(inn & mask1);      /* remove dispensable bits and store */

  while (joflow != 0)               /* loop over other bytes in sample */
  {
    retval <<= 5;                    /* multiply with 32 for next byte */
    
    // read next
    is.get(inchar);
    while (inchar == '\n') { is.get(inchar); }
    if (isspace(inchar))
      throw Terror("ERROR (CM6::decode): illegal whitespace");
    if (is.eof())
      throw Terror("ERROR (CM6::decode): illegal end of file");

    /* now the same procedure as above */
    k = int(int(inchar) & m127);
    inn = ichar[k];
    joflow = (inn & ioflow);                /* get continuation bit if any */
    retval = retval + intT(inn & mask2);  /* remove bits and store */

  } /* finish up sample if there is no further continuation bit */

  if (jsign != 0) retval = -retval;           /* evaluate sign bit */

  return(retval);
} // decode

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