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;
> }
>
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/Floats-in-Microsoft-Basic-format-tp3732456p3732456.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.