On 10/08/2011 5:58 AM, taraxacum wrote:
Hi all,
I need to convert a floating point value from Microsoft Basic format to IEEE
format.
There's a simple way to achieve this in R or I have to write my own
function?
(e.g. convert the C code below)
You'll need to write your own function. It can be very similar to what
you have below, except:
- you'll need to produce double rather than single (easy, just produce
a single and assign to a double, C does the conversion for you)
- you need to change the args to your function to some that R understands.
Duncan Murdoch
thanks
t
#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;
}
--
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