Re^2: When 1e-298L != 1e-298L

C:\test>r80test

Is "r80test" readily available ? (Could be handy.)

kcott's post demonstrates that the discrepancy also occurs when the nvtype is 'double' - but not universally according to some quick testing that I've just done. (The discrepancy occurs with gcc-4.6.3 on linux, and MSVC++ 7.0 on MS Windows, but not gcc-4.7.0 on MS Windows. In all instances the compiler I've used is the compiler that actually built perl. It seems that the behaviour does depend upon the compiler in use, not upon the version number of perl, but that's not properly tested yet.)

I've just rewritten the demo code so that it's also portable to perls whose nvtype is 'double'. (See my reply to kcott's post.)

And now I find that the mpfr library is providing varying results on linux and windows. It shouldn't do that, but I'll have to check the versions of mpfr that I'm running. (It may simply be a bug in an earlier version that has been fixed.)

Thanks Buk.

Cheers,
Rob

Comment on Re^2: When 1e-298L != 1e-298L

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Re^3: When 1e-298L != 1e-298L by BrowserUk (Patriarch) on Oct 25, 2013 at 00:25 UTC
Is "r80test" readily available ? (Could be handy.) It's written in D, which has a native 80-bit FP type available. The code looks like this: `import std.stdio; import std.format; void main( string[] args ) { real r; ubyte ubp = cast(ubyte)&r; foreach( line; stdin.byLine ) { formattedRead( line, " %f ", &r ); writef( "%20.18g : ", r ); for( int i = r.sizeof -1; i >= 0; --i ) { writef( "%08.8b ", ubp[i] ); } writeln(); } }` [download] If you don't want to be bothered with installing/learning D, I can send you the executable? With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]
Re^4: When 1e-298L != 1e-298L by syphilis (Archbishop) on Oct 25, 2013 at 01:41 UTC
If you don't want to be bothered with installing/learning D, I can send you the executable? Send it over would be great !! (I'll /msg you the address.) Having another tool that outputs this info would be handy. I'm currently using a "print_binary" function from tests/tmpfr_set_ld.c (in the mpfr source) but it purports to show me the actual value I pass it, not the correct value ... and it's starting to look like the 2 can differ. At some point I might like to give D a try. I see that there's a GCC variant (gcd), but I gather that it's the one provided by Digital Mars (dmd, version 2) that would normally be recommended ? Cheers, Rob	[reply]