Binary File Reading : Metastock

[malv]

Jack wrote:
> Hi
>
> I am having a little trouble trying to read a binary file, I would like
> to write an ascii to Metastock converter in python but am not having a
> lot of success.
>
> The file formats are
>
> http://sf.gds.tuwien.ac.at/00-pdf/m/mstockfl/MetaStock.pdf
>
>
> If any one can point me in the right direction it would be much
> appreciated.
>
> So far I have tried opening file "rb" then trying to use struct and
> then binascii but I am not too sure what I should be doing and fuction
> I should be using in binascii ?
>
>
>
> TIA
Jack,
What you may not realize is that Metastock is using an oddball floating
point format.
I have not looked at this for many years now but remember using a small
VB-callable dll with functions BasicToIEEE and IEEEToBasic. This may
help you in recoding conversions into Python.

float BasicToIEEE (unsigned char *value)

{ float result;

  unsigned char *msbin =   (unsigned char *)  value;

  unsigned char *ieee =    (unsigned char *) &result;

  unsigned char  sign     = 0x00;

  unsigned char  ieee_exp = 0x00;

  int i;

  /* MS Binary Format                         */

  /* byte order =>    m3 | m2 | m1 | exponent */

  /* m1 is most significant byte => sbbb|bbbb */

  /* m3 is the least significant byte         */

  /*      m = mantissa byte                   */

  /*      s = sign bit                        */

  /*      b = bit                             */

  sign = msbin[2] & 0x80;      /* 1000|0000b  */

  /* IEEE Single Precision Float Format       */

  /*    m3        m2        m1     exponent   */

  /* mmmm|mmmm mmmm|mmmm emmm|mmmm seee|eeee  */

  /*          s = sign bit                    */

  /*          e = exponent bit                */

  /*          m = mantissa bit                */

  for (i=0; i<4; i++) ieee[i] = 0;

  /* any msbin w/ exponent of zero = zero */

  if (msbin[3] == 0) return 0;

  ieee[3] |= sign;

  /* MBF is bias 128 and IEEE is bias 127. ALSO, MBF places   */

  /* the decimal point before the assumed bit, while          */

  /* IEEE places the decimal point after the assumed bit.     */

  ieee_exp = msbin[3] - 2;    /* actually, msbin[3]-1-128+127 */

  /* the first 7 bits of the exponent in ieee[3] */

  ieee[3] |= ieee_exp >> 1;

  /* the one remaining bit in first bin of ieee[2] */

  ieee[2] |= ieee_exp << 7;

  /* 0111|1111b : mask out the msbin sign bit */

  ieee[2] |= msbin[2] & 0x7f;

  ieee[1] = msbin[1];

  ieee[0] = msbin[0];

  return (result);

}



bool IEEEToBasic (float *value, unsigned char *result)

{  unsigned char *ieee     = (unsigned char *) value;

   unsigned char *msbin    = (unsigned char *) result;

   unsigned char sign      = 0x00;

   unsigned char msbin_exp = 0x00;

   int i;

   /* See _fmsbintoieee() for details of formats   */

   sign = ieee[3] & 0x80;

   msbin_exp |= ieee[3] << 1;

   msbin_exp |= ieee[2] >> 7;

   /* An ieee exponent of 0xfe overflows in MBF    */

   if (msbin_exp == 0xfe) return (FALSE);

   msbin_exp += 2;   /* actually, -127 + 128 + 1 */

   for (i=0; i<4; i++) msbin[i] = 0;

   msbin[3] = msbin_exp;

   msbin[2] |= sign;

   msbin[2] |= ieee[2] & 0x7f;

   msbin[1] = ieee[1];

   msbin[0] = ieee[0];

   return (TRUE);

}

Good luck,
malv