S'Is_nan or S'Is_inf?
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From: Dmitry A. Kazakov on 17 Jul 2010 03:40 On Fri, 16 Jul 2010 22:35:14 +0000 (UTC), Warren wrote: > I'll need > to test it on other platforms, but hopefully most if not all > IEEE platforms will support this. IEEE representations have more than +Inf, -Inf and NaN. There are other objects: +0, -0, denormalized numbers (see attribute 'Denorm). Some have dubious semantics: with Ada.Text_IO; use Ada.Text_IO; procedure IEEE_Zeros is Zero : Float := 0.0; N0 : Float := 0.0 / (-1.0 / Zero); begin Put_Line ("-0 =" & Float'Image (N0) & " 0 = " & Float'Image (Zero)); Put_Line ("-0 = 0 " & Boolean'Image (N0 = Zero)); Put_Line ("-0 < 0 " & Boolean'Image (N0 < Zero)); end IEEE_Zeros; Negative zero is zero but not equal to, etc. What are you trying to achieve? Because in automation we have the rule never ever let IEEE cripples slip through. Don't read them, don't write them, don't compute them. The solution Simon suggested is basically everything Ada programmer should know about IEEE 754! (:-)) -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de
From: Warren on 19 Jul 2010 13:04 Simon Wright expounded in news:m2tynytykr.fsf(a)pushface.org: > Warren <ve3wwg(a)gmail.com> writes: > >> To detect NaN then, this seems to work: > > See above, where Jean-Pierre said > >> If X /= X, then X is a NaN (see http://en.wikipedia.org/wiki/NaN) Thanks. I later had a head slapping moment on the weekend where I had figured that out. ;-) Warren
From: Warren on 19 Jul 2010 13:18 Dmitry A. Kazakov expounded in news:5xj0ja9xywto$.3ncqua6onpoa.dlg(a)40tude.net: > On Fri, 16 Jul 2010 22:35:14 +0000 (UTC), Warren wrote: > IEEE representations have more than +Inf, -Inf and NaN. There are > other objects: +0, -0, denormalized numbers (see attribute 'Denorm). > Some have dubious semantics: Ya, I know about those. As indicated in my other reply, I did eventually figure out that if F /= F, then it is NaN (for some reason, I didn't see this at first). > What are you trying to achieve? Because in automation we have the rule > never ever let IEEE cripples slip through. Don't read them, don't > write them, don't compute them. In my Basic interpreter, I'll raise an error if you try to use these IEEE values in an argument to a function or try to compute something with an operator (here NOT 'Valid is sufficient). However, if the expression result is one of these, I do allow it to be assigned to a [basic] variable. So then the user needs a (basic) function to test if the variable V is +/- infinity or NaN. So in basic, ISNAN(X) returns 1 if NaN, else zero, for example. In the C version of the interpreter, I relied upon C functions for these tests. Ada clearly does not need these C functions, which is bliss for the Ada rewrite. Thanks for everyone's help. Warren
From: Randy Brukardt on 19 Jul 2010 19:15 "Warren" <ve3wwg(a)gmail.com> wrote in message news:Xns9DB6AD1651560WarrensBlatherings(a)81.169.183.62... > Is there any is not-a-number or is-infinity test support in > Ada05+ (for floats)? Is there any being planned? We considered it for Ada 2005 (see AI95-0315-1). It was abandoned because of the large impact on implementations and the weak demand (hardly any user requests). John Barnes mentions this in the Ada 2005 Rational: http://www.adaic.com/standards/05rat/html/Rat-9-3-3.html It wasn't resurrected for Ada 2012, so there won't be any change here. BTW, GNAT seems to pass through a lot of IEEE stuff, thus you can write examples using that. Other Ada compilers (at least as of 2003-4 timeframe) vary widely in what is exposed (Janus/Ada only supports IEEE denormal numbers; everything else raises Constraint_Error before it is stored). Randy.
From: Warren on 20 Jul 2010 10:12 Randy Brukardt expounded in news:i22m9q$cd4$1(a)munin.nbi.dk: > "Warren" <ve3wwg(a)gmail.com> wrote in message > news:Xns9DB6AD1651560WarrensBlatherings(a)81.169.183.62... >> Is there any is not-a-number or is-infinity test support in >> Ada05+ (for floats)? Is there any being planned? > > We considered it for Ada 2005 (see AI95-0315-1). It was abandoned > because of the large impact on implementations and the weak demand > (hardly any user requests). > > John Barnes mentions this in the Ada 2005 Rational: > http://www.adaic.com/standards/05rat/html/Rat-9-3-3.html > > It wasn't resurrected for Ada 2012, so there won't be any change here. > > BTW, GNAT seems to pass through a lot of IEEE stuff, thus you can > write examples using that. Other Ada compilers (at least as of 2003-4 > timeframe) vary widely in what is exposed (Janus/Ada only supports > IEEE denormal numbers; everything else raises Constraint_Error before > it is stored). > > Randy. Very interesting. My project is fairly dependant on gnat (at the moment at least), so things should work ok. I'm not personally a fan of these special IEEE values, but they crop up in 3rd party libraries like the GSL etc. or in the reading of binary values from a file. Warren
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