From: "\"Jürgen Urban\"" <JuergenUrban@gmx.de>
To: "Maciej W. Rozycki" <macro@codesourcery.com>
Cc: gcc-patches@gcc.gnu.org, binutils@sourceware.org
Subject: Re: Support for MIPS r5900
Date: Sun, 20 Jan 2013 21:43:00 -0000 [thread overview]
Message-ID: <20130120214241.59480@gmx.net> (raw)
In-Reply-To: <alpine.DEB.1.10.1301172232280.4834@tp.orcam.me.uk>
Hello Maciej,
> > I tested the calculation with the type "float".
> > ABI o32 with -mhard-float and -msingle-float produces the following
> results:
> > 1.000000 (0x3f800000) / 0.000000 (0x00000000) = nan (0x7fffffff)
> > 0.000000 (0x00000000) / 0.000000 (0x00000000) = nan (0x7fffffff)
> > 0.000000 (0x00000000) / nan (0x7fc00000) = 0.000000 (0x00000000)
> > 1.000000 (0x3f800000) + 1.000000 (0x3f800000) = 2.000000 (0x40000000)
> > 1.000000 (0x3f800000) + inf (0x7f800000) = inf (0x7f800000)
> > inf (0x7f800000) + inf (0x7f800000) = nan (0x7fffffff)
> > inf (0x7f800000) + -inf (0xff800000) = 0.000000 (0x00000000)
> > nan (0x7fc00000) + nan (0x7fc00000) = nan (0x7fffffff)
> > nan (0x7fc00000) + nan (0xffc00000) = 0.000000 (0x00000000)
> >
> > The r5900 manual calls the result of 0/0 Fmax. So 0x7fffffff seems to be
> Fmax.
>
> So presumably you can get 0x7fffffff as an arithmetic result of a
> calculation involving regular numbers as well, right? Say 0x7f7ffffe +
> 0x74000000 (using the binary-encoded notation)? That would be beyond the
> IEEE-754 single range.
The FPU of the r5900 calculates the following:
340282306073709652508363335590014353408.000000 (0x7f7ffffd) + 40564819207303340847894502572032.000000 (0x74000000) = 340282346638528859811704183484516925440.000000 (0x7f7fffff)
340282326356119256160033759537265639424.000000 (0x7f7ffffe) + 40564819207303340847894502572032.000000 (0x74000000) = inf (0x7f800000)
340282346638528859811704183484516925440.000000 (0x7f7fffff) + 40564819207303340847894502572032.000000 (0x74000000) = inf (0x7f800000)
inf (0x7f800000) + 40564819207303340847894502572032.000000 (0x74000000) = nan (0x7f800001)
nan (0x7f800001) + 40564819207303340847894502572032.000000 (0x74000000) = nan (0x7f800002)
nan (0x7f900000) + 40564819207303340847894502572032.000000 (0x74000000) = nan (0x7f900001)
nan (0x7f900001) + 40564819207303340847894502572032.000000 (0x74000000) = nan (0x7f900002)
nan (0x7ffffff1) + 40564819207303340847894502572032.000000 (0x74000000) = nan (0x7ffffff2)
nan (0x7ffffffc) + 40564819207303340847894502572032.000000 (0x74000000) = nan (0x7ffffffd)
nan (0x7ffffffd) + 40564819207303340847894502572032.000000 (0x74000000) = nan (0x7ffffffe)
nan (0x7ffffffe) + 40564819207303340847894502572032.000000 (0x74000000) = nan (0x7fffffff)
nan (0x7fffffff) + 40564819207303340847894502572032.000000 (0x74000000) = nan (0x7fffffff)
So it seems that it interprets nan and inf as normal numbers, but it stops at 0x7fffffff. So 0x7fffffff should be interpreted as overflow.
Best regards
Jürgen
next prev parent reply other threads:[~2013-01-20 21:43 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-06 22:57 "Jürgen Urban"
2013-01-07 17:15 ` Jeff Law
2013-01-07 20:44 ` Richard Sandiford
2013-01-07 21:52 ` Richard Sandiford
2013-01-08 0:23 ` Maciej W. Rozycki
2013-01-08 7:28 ` Richard Sandiford
2013-01-08 17:24 ` Maciej W. Rozycki
2013-01-08 18:25 ` Richard Sandiford
2013-01-08 22:34 ` "Jürgen Urban"
2013-01-10 23:25 ` Maciej W. Rozycki
2013-01-11 9:49 ` Richard Sandiford
2013-01-11 16:55 ` Maciej W. Rozycki
2013-01-13 14:16 ` "Jürgen Urban"
2013-01-14 18:42 ` Maciej W. Rozycki
2013-01-17 22:21 ` "Jürgen Urban"
2013-01-17 23:23 ` Maciej W. Rozycki
2013-01-19 10:53 ` Richard Sandiford
2013-01-20 21:43 ` "Jürgen Urban" [this message]
2013-01-08 4:22 ` Jeff Law
2013-01-08 7:22 ` Richard Sandiford
2013-01-08 22:49 ` "Jürgen Urban"
2013-01-09 5:25 ` Jeff Law
2013-01-10 22:59 ` "Jürgen Urban"
2013-01-11 4:41 ` Jeff Law
2013-01-08 7:16 ` Richard Sandiford
2013-01-08 21:30 ` "Jürgen Urban"
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