[Tcl-bugs] [ tcl-Bugs-532537 ] Buggy Windows strtod() ?

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Bugs item #532537, was opened at 2002-03-20 11:03
Message generated for change (Comment added) made by kennykb
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Category: 11. Conversions from String
Group: obsolete: 8.3.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
>Assigned to: Kevin B KENNY (kennykb)
Summary: Buggy Windows strtod() ?

Initial Comment:

Try following script under Window NT:

proc testDouble {} {
    set a0 [expr {double(2.63624325102e-308)}]
    set b  [expr {double(0.19024736769)}]
    set a  $a0

    set count 30
    while {[incr count -1] > 0} {
        # just make a lose its double repr
        # string length $a
        puts "a = $a"
        set a [expr {$a*$b}]
    }
}

a is decreasing until 0.0.

Now uncomment the [string length] line, and try it
again. This gives the error message:
  can't use non-numeric string as operand of "*"
(Is it possible to have "floating-point value too
small to represent" ?)

This work fine under Linux. Can I conclude that my
Windows NT strtod() is buggy ?


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>Comment By: Kevin B KENNY (kennykb)
Date: 2005-01-25 10:20

Message:
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This problem is in the scope of TIP #132 -
 assigning it to myself.

The fix may be as simple as including 
strtod.obj in COMPAT_OBJS, depending on
whether compat/strtod.c has the same bug.
But depending on the native C library in this
area has proven to be a mistake; FP conversion
bugs have been recurrent.

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Comment By: Eric Boudaillier (beric)
Date: 2002-03-25 08:09

Message:
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Being surprised to found in <float.h>
#define DBL_MIN 2.2250738585072014e-308
I have tried a c code declaring two double:
  2.63624325102e-308
  5.01538339097e-309
It compile on both windows and linux, linux strtod()
works with both string repr, windows (VC6) fails with
errno == ERANGE for the second.

The following page show that doubles have normalized
and denormalized representation:
 http://babbage.cs.qc.edu/courses/cs341/IEEE-
754references.html
DBL_MIN is the minimum normalized double.

It looks like windows's strtod() doesn't work on
denormalized double, whereas linux does.



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Comment By: Donal K. Fellows (dkf)
Date: 2002-03-25 05:51

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Can duplicate this in 8.3.4 under Solaris/SPARC as long as I
remember to uncomment the [string length] (which acts as a
complete destroyer of the double rep, as it converts to the
wide-character internal rep)

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Comment By: Eric Boudaillier (beric)
Date: 2002-03-25 03:16

Message:
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Have you uncommented the [string length] line ?

% expr {double(4.94065645841e-324)}
floating-point value too small to represent
% expr {double(5.92665091618e-317)}
floating-point value too small to represent

with both AS 8.3.4.1 and 8.4a4 compiled with VC6
on two NT 4 station.



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Comment By: Jeffrey Hobbs (hobbs)
Date: 2002-03-22 19:09

Message:
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perhaps ... but I get the following on Win2K with a VC++6 
compiled 8.3.4 (ActiveTcl 8.3.4.2):

(tkcon) 50 % testDouble
a = 2.63624325102e-308
a = 5.01538339097e-309
a = 9.54163488088e-310
a = 1.81527091955e-310
a = 3.45350514088e-311
a = 6.57020262356e-312
a = 1.24996375432e-312
a = 2.37802313969e-313
a = 4.52412642615e-314
a = 8.60703143633e-315
a = 1.63746507553e-315
a = 3.1152341918e-316
a = 5.92665091618e-317
a = 1.12752993739e-317
a = 2.14509469586e-318
a = 4.08098223465e-319
a = 7.76374755875e-320
a = 1.47725628107e-320
a = 2.81123352484e-321
a = 5.33590897509e-322
a = 1.03753785627e-322
a = 1.97626258336e-323
a = 4.94065645841e-324
a = 0.0
a = 0.0
a = 0.0
a = 0.0
a = 0.0
a = 0.0


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