Re: [TCLCORE] TIP #347: Add 'string is bignum' to the 'string is' Subcommand

[Donald G P. <dg...@ni...>]

Daniel A. Steffen wrote:
> On Wed, Feb 11, 2009 at 22:37, Daniel A. Steffen
> <da...@ca...> wrote:
>> sure, my point was that [string is double] accepts all bignums,
>> including those that cannot fit into a C double without loss of
>> precision, or even those bigger than DBL_MAX...
> 
> leading to things like this:
> 
> % set x [expr {10**400}]
> 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
> % string is double $x
> 1
> % expr {double($x)}
> Inf
> 
> from the manpage text, I would not have expected an overflowing double
> to be acceptable:
> 
>               double      Any of the valid forms for a  double  in  Tcl,  with
>                           optional   surrounding   whitespace.    In  case  of
>                           under/overflow in the value, 0 is returned  and  the
>                           varname will contain -1.

Looks like an overlooked doc update.

 From TIP 249, "Incompatibillities":

Third, Tcl_GetDoubleFromObj will be both more and less permissive than 
before. It will no longer accept constants with a leading zero and no 
decimal point or 'E' that are invalid octal numbers. On the other hand, 
it will accept constants that are too large to fit in a Tcl_WideInt; 
somewhat surprisingly, string repeat 9 50 cannot today be interpreted as 
a double. string is double will follow Tcl_GetDoubleFromObj in what it 
considers acceptable. Any string that is accepted as either an integer 
or a double by expr will be accepted in Tcl_GetDoubleFromObj, and only 
those strings will be accepted.


-- 
| Don Porter          Mathematical and Computational Sciences Division |
| don...@ni...             Information Technology Laboratory |
| http://math.nist.gov/~DPorter/                                  NIST |
|______________________________________________________________________|