Converting between Microsoft Binary and IEEE formats
1400 Converting between Microsoft Binary and IEEE formats
Last update 06/11/96
//
// The following are implementations of Microsoft RTL functions
// not include in the Borland RTL.
//
// Functions:
// _fmsbintoieee()
// _fieeetomsbin()
// _dmsbintoieee()
// _dieeetomsbin()
//
// These functions convert back and forth from Microsoft Binary
// Format to IEEE floating point format.
//
// As with the Microsoft RTL functions,
//
// The argument srcX points to the value to be converted and the
// result is stored at the location given at destX.
//
// These routines do not handle IEE NAN's and infinities. IEEE
// denormals are treated as 0's.
//
// Return:
//
// These functions return 0 if the conversion is successful and 1
// if the conversion causes an overflow.
//
//
//
// Examples of the use of these functions can be found on-line as
// MSBIN.ZIP.
//
//--------------------------------------------------------------------
#include <string.h> /* for strncpy */
int _fmsbintoieee(float *src4, float *dest4)
{
unsigned char *msbin = (unsigned char *)src4;
unsigned char *ieee = (unsigned char *)dest4;
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 0;
}
int _fieeetomsbin(float *src4, float *dest4)
{
unsigned char *ieee = (unsigned char *)src4;
unsigned char *msbin = (unsigned char *)dest4;
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 1;
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 0;
}
int _dmsbintoieee(double *src8, double *dest8)
{
unsigned char msbin[8];
unsigned char *ieee = (unsigned char *)dest8;
unsigned char sign = 0x00;
unsigned int ieee_exp = 0x0000;
int i;
/* A manipulatable copy of the msbin number */
strncpy((char *)msbin,(char *)src8,8);
/* MS Binary Format */
/* byte order => m7 | m6 | m5 | m4 | m3 | m2 | m1 | exponent */
/* m1 is most significant byte => smmm|mmmm */
/* m7 is the least significant byte */
/* m = mantissa byte */
/* s = sign bit */
/* b = bit */
sign = msbin[6] & 0x80; /* 1000|0000b */
/* IEEE Single Precision Float Format */
/* byte 8 byte 7 byte 6 byte 5 byte 4 and so on */
/* seee|eeee eeee|mmmm mmmm|mmmm mmmm|mmmm mmmm|mmmm ... */
/* s = sign bit */
/* e = exponent bit */
/* m = mantissa bit */
for (i=0; i<8; i++) ieee[i] = 0;
/* any msbin w/ exponent of zero = zero */
if (msbin[7] == 0) return 0;
ieee[7] |= sign;
/* MBF is bias 128 and IEEE is bias 1023. ALSO, MBF places */
/* the decimal point before the assumed bit, while */
/* IEEE places the decimal point after the assumed bit. */
ieee_exp = msbin[7] - 128 - 1 + 1023;
/* First 4 bits of the msbin exponent */
/* go into the last 4 bits of ieee[7] */
ieee[7] |= ieee_exp >> 4;
/* The last 4 bits of msbin exponent */
/* go into the first 4 bits of ieee[6] */
ieee[6] |= ieee_exp << 4;
/* The msbin mantissa must be shifted to the right 1 bit. */
/* Remember that the msbin number has its bytes reversed. */
for (i=6; i>0; i--)
{
msbin[i] <<= 1;
msbin[i] |= msbin[i-1] >> 7;
}
msbin[0] <<= 1;
/* Now the mantissa is put into the ieee array starting in */
/* the middle of the second to last byte. */
for (i=6; i>0; i--)
{
ieee[i] |= msbin[i] >> 4;
ieee[i-1] |= msbin[i] << 4;
}
ieee[0] |= msbin[0] >> 4;
/* IEEE has a half byte less for its mantissa. If the msbin */
/* number has anything in this last half byte, then there is */
/* an overflow. */
if (msbin[0] & 0x0f)
return 1;
else
return 0;
}
int _dieeetomsbin(double *src8, double *dest8)
{
unsigned char ieee[8];
unsigned char *msbin = (unsigned char *)dest8;
unsigned char sign = 0x00;
unsigned char any_on = 0x00;
unsigned int msbin_exp = 0x0000;
int i;
/* Make a clobberable copy of the source number */
strncpy((char *)ieee,(char *)src8,8);
for (i=0; i<8; i++) msbin[i] = 0;
/* If all are zero in src8, the msbin should be zero */
for (i=0; i<8; i++) any_on |= ieee[i];
if (!any_on) return 0;
sign = ieee[7] & 0x80;
msbin[6] |= sign;
msbin_exp = (unsigned)(ieee[7] & 0x7f) * 0x10;
msbin_exp += ieee[6] >> 4;
if (msbin_exp-0x3ff > 0x80) return 1;
msbin[7] = msbin_exp - 0x3ff + 0x80 + 1;
/* The ieee mantissa must be shifted up 3 bits */
ieee[6] &= 0x0f; /* mask out the exponent in the second byte
*/
for (i=6; i>0; i--)
{
msbin[i] |= ieee[i] << 3;
msbin[i] |= ieee[i-1] >> 5;
}
msbin[0] |= ieee[0] << 3;
return 0;
}
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