Been working on updating 8.5 docs concerning all the numerics changes,
and ran across something I need more people to see and comment on.

TIP 132 proposes, in part,

  "Tcl_GetDoubleFromObj shall treat +Inf and -Inf as it does any
   ordinary floating point number, and return an error for NaN."
   
And the implementation of Tcl_GetDoubleFromObj() has followed that
prescription and now returns TCL_ERROR when the Tcl_Obj holds a NaN
value.

The trouble I have with that is this code example:

    objPtr = Tcl_NewDoubleObj(d1);
    code = Tcl_GetDoubleFromObj(interp, objPtr, &d2);
    
In all Tcl 8 releases up to now, a programmer could rely on code now
having the value TCL_OK, and the variable d2 holding a copy of the
variable d1.

With the TIP 132 change, whenever d1 holds NaN, code will get TCL_ERROR
and d2 will remain unchanged.

I think this means that extensions lose the ability to pass the NaN
value through Tcl.  I have to believe that will make someone, somewhere
unhappy.

It seems strange to me that we drop this capability just at the time
when we've purged all the problems with converting a NaN value to and
from a string rep.  Just when shimmering will no longer cause us 
trouble, we just opt out of supporting this value?

Can someone confirm this incompatibility, and explain to me again what
the purpose of this change was?  What we gain in exchange for this loss?

| Don Porter          Mathematical and Computational Sciences Division |
| donald.porter@[...].gov             Information Technology Laboratory |
| http://math.nist.gov/~DPorter/                                  NIST |
|______________________________________________________________________|



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