[cmucl-imp] [cmucl-help] NaN

[Marco Antoniotti]

Hi Ray

maybe we can just have this discussion here.

I am not a person who knows all that much about the IEEE fine details, but I would like to have a “higher level” portable API to access IEEE NaNs, infinities, and rounding modes.  I am kind of familiar with the C99 API.

Would you like to have an API consisting of something like (given a package “M”, not its real name) the following?  Assuming all “quiet” NaNs.

Parameter NaN

Constant <float-length>-float-positive-infinity
Constant <float-length>-float-negative-infinity

Type rounding-mode (member :positive :negative :toward-zero :to-nearest)

Struct floating-point-configuration

Function current-floating-point-configuration
Function (setf current-floating-point-configuration)

Macro with-floating-point-configuration

Function current-rounding-mode
Function (setf current-rounding-mode)

Macro with-rounding-mode


Details to be filled…
This covers CMUCL and SBCL and (mostly) LW.  CCL could be bent to comply.  For ECL and ABCL pressures can be made; ACL is another story.

What do you think?

MA





> On Jan 8, 2017, at 23:58 , Raymond Toy <toy.raymond at gmail.com> wrote:
> 
> Oops. Meant to reply to all.
> 
> ---------- Forwarded message ----------
> From: Raymond Toy <toy.raymond at gmail.com>
> Date: Sun, Jan 8, 2017 at 10:00 AM
> Subject: Re: [cmucl-help] NaN
> To: Marco Antoniotti <marcoxa at cs.nyu.edu>
> 
> 
> 
> 
> On Sat, Jan 7, 2017 at 3:44 PM, Marco Antoniotti <marcoxa at cs.nyu.edu> wrote:
> 
>> Hi
>> 
>> I am fiddling around with some IEEE floating points.
>> 
>> I see that the following code produces a (almost nice) “quiet” NaN.
>> 
>> CL-USER> (ext:with-float-traps-masked (:invalid)
>>           (* 0.0 ext:double-float-positive-infinity))
>> #<DOUBLE-FLOAT Quiet NaN>
>> 
>> Alas, there seem to be no way to tell the compiler that we are actually
>> executing the multiplication within the ext:with-float-traps-masked.  This
>> prevents us, for example to do things like
>> 
>> (defparameter NAN (ext:with-float-traps-masked (:invalid)
>>                    (* 0.0 ext:double-float-positive-infinity))
>> 
>> in a file and having it compiled “nicely”.  The compiler complains (warns)
>> about a FLOATING-POINT-INVALID-OPERATION
>> 
>> ; In: DEFPARAMETER NAN
>> 
>> ;   (* 0.0 EXTENSIONS:DOUBLE-FLOAT-POSITIVE-INFINITY)
>> ; Warning: Lisp error during constant folding:
>> ; Arithmetic error FLOATING-POINT-INVALID-OPERATION signalled.
>> ; Operation was *, operands (0.0d0 #.EXT:DOUBLE-FLOAT-POSITIVE-INFINITY).
>> 
> 
> ​What version? I don't get any warnings from snapshot-2017-01.​
> 
> 
>> 
>> Note that the value is then assigned correctly, but it seems very hard (at
>> least I did not figure out how to do it) to get to the constant folding
>> time to catch and muffle the warning.
>> 
>> Any ideas?
>> 
> 
> ​Since you're using cmucl-specific functions, you could always just
> construct the NaN directly using kernel:make-double-float.  Something like
> (kernel:make-double-float -524288 0)​
> 
> 
> -- 
> Ray
> 
> 
> 
> -- 
> Ray
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--
Marco Antoniotti