On Fri, 2 Feb 2007 23:43:05 +0100David Nečas (Yeti) <yeti@xxxxxxxxxxxxxxx> wrote: >On Fri, Feb 02, 2007 at 04:30:17PM -0500, zentara wrote:>> Please pardon my basic questions, but I am self taught>> and run into questions I can't solve thru googling.>>The problem of this question is rather that it's completely>unrelated to Gtk+. Well I'm wondering why the header defines G_PI to 49 places(if I counted right), if the biggest Gtk2 data type only holds precisionto 15? So I'm wondering if someone knew something about gtk2that would handle such a big number? >> I see that G_PI is defined in the header to>> 3.14159265358979323846>>I wonder where you found this. gtypes.h defines G_PI:>> #define G_PI 3.1415926535897932384626433832795028841971693993751 Yeah you are right. I copied it off g.lib-2.12.9/docs/reference/glib/html/lib-Numerical-Definitions.html correctly, but I must have made a cut-n-paste typo somewhere. Sorry.It was still greater prescision than I could get with Long Double. >>The standard IEEE 754 double precision floating point type>has 64 bits, of which 52 bits is mantissa, that's 15-16>decimal digits. The standard type obviously has the same>precision everywhere because if it differed it would not be>the standard type any more.>>Both i386 (or rather its 387 math coprocessor) and x86_64>are capable of calculation with 80bit floating point>numbers, mantissa is 64 bits, that's 19-20 decimal digits.>These numbers are available as the `long double' type. long>double is implementation-defined, it can look differently on>other platforms.>>Yeti Thank you for your help. After looking thru a bunch of comp.lang.cposts, where this was asked, the best answer I saw was "C only guarantees 10 digits of precision with double and long double.Since IEEE representations have become widespread 15 or so is commonbut the requirement is still only 10. " And that is what I'm seeing..... 15 decimal places accuracy. It also answered a question lurking in the back of my mind, whyFortran is still so widely used in numerical computation insteadof c. zentara -- I'm not really a human, but I play one on earth.http://zentara.net/japh.html_______________________________________________gtk-list mailing listgtk-list@xxxxxxxxxxxxx://mail.gnome.org/mailman/listinfo/gtk-list
