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/.../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
