Re: Handling numeric types in interpreter

From	James Kuyper <jameskuyper@verizon.net>
Newsgroups	comp.lang.c
Subject	Re: Handling numeric types in interpreter
Date	2015-07-26 18:57 -0400
Organization	Self
Message-ID	<55B565C8.5000302@verizon.net> (permalink)
References	(7 earlier) <aa38ral5h5j538fqkdtdfc8cub5tl8b4a5@4ax.com> <55B41602.1030903@verizon.net> <qfr8ra1c730jpbf9hfjqahq9vfhhfr6ofj@4ax.com> <mp2jfn$79m$1@dont-email.me> <hijaratgjp79vv08mn4sbgt7k7gdr1mnhh@4ax.com>

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On 07/26/2015 05:28 PM, Robert Wessel wrote:
> On Sun, 26 Jul 2015 08:24:50 -0400, James Kuyper
> <jameskuyper@verizon.net> wrote:
> 
>> On 07/26/2015 01:23 AM, Robert Wessel wrote:
>>> On Sat, 25 Jul 2015 19:04:34 -0400, James Kuyper
>>> <jameskuyper@verizon.net> wrote:
>>>
>>>> On 07/25/2015 06:31 PM, Robert Wessel wrote:
>>>>> On Sat, 25 Jul 2015 17:48:59 -0400, James Kuyper
>>>>> <jameskuyper@verizon.net> wrote:
>>>>>
>>>>>> On 07/25/2015 04:46 PM, Robert Wessel wrote:
>>>>>>> On Sat, 25 Jul 2015 06:12:16 -0700 (PDT), Malcolm McLean
>>>>>>> <malcolm.mclean5@btinternet.com> wrote:
>>>> ...
>>>>>>>> long double being present or not is important. Actually legitimate
>>>>>>>> values in a tiff file for a tiff reader can't go over 2^50 as far as 
>>>>>>>> I know, so double is OK.
>>>>>>>
>>>>>>>
>>>>>>> Doubles are required to have 2**50 in their range, but are not
>>>>>>
>>>>>> I'm curious - where is this specified? I went searching for a
>>>>>> specification of the TIFF format, and found
>>>>>> <http://partners.adobe.com/public/developer/tiff/index.html>. I couldn't
>>>>>> find it in any of the documents listed there. Did I find the wrong
>>>>>> documents?
>>>>>
>>>>>
>>>>> I was referring to the C requirements for doubles, which require a
>>>>> range of 10**-37..10**37 and 10 decimal digit of precision for a
>>>>> double.  The first requirement accommodates 2**50, the second does
>>>>> not.  The TIFF spec is that floats and double are IEEE format (which
>>>>> has a 11 bit exponent and a 53 bit significand).
>>>>
>>>> In that case, the limit that Malcolm should be using should be derived
>>> >from the IEEE double specification, and is therefore
>>>> 0X1.fffffffffffffP1023, not 2^50.
>>>
>>>
>>> No, he has to be able to process all values that can *validly* occur
>>> in a TIFF file, or at least in a TIFF file his code purports to
>>> handle.  If an invalid value is found (and they all ned to be checked)
>>> he needs to return INVALID_TIFF_FILE.  I'm not commenting on what the
>>> actual range of valid values are.
>>
>> Well, unlike you, I was commenting on the actual range of valid values.
>> He seems to think the upper limit is 2^50, and I was asking about the
>> basis for that limit. His wording imply that it's a limit that applies
>> to all TIFF files, not just the particular TIFF files his reader is
>> intended to process. As far as I can tell, since the TIFF specification
>> says that DOUBLE is supposed to have IEEE format (and presumably,
>> specifically the IEEE format for double precision),
>> 0X1.fffffffffffffP1023 is the correct upper limit. As a result, on some
>> machines 'double' might not have enough range: DBL_MAX is allowed to be
>> as low as 1e37. Of course, LDBL_MAX is also allowed to be as low as 1e37
>> - but it will never be smaller than DBL_MAX, so using 'long double' is
>> marginally safer. He's free to assume that all machines this code will
>> ever be ported to will have IEEE doubles, but if so, he should state
>> that as a requirement rather than silently failing to address the issue.
> 
> 
> Just because a value is stored as an IEEE float doesn't mean that all
> values possible in that representation are meaningful or valid.
> Consider a medical application that stored a human's mass and height
> in floats - no one would expect it to produce valid results if it
> encountered a record specifying a 20,000kg or 40m human.  OTOH, it's
> perfectly reasonable to expect that the application would (safely)
> refuse to process such a record with an appropriate error message.

Again, that's application-specific. His wording implied a reason
specific to TIFF for a limit that all TIFF readers can rely upon TIFF
data not to exceed. Your argument suggests that it's a completely
arbitrary limit based upon "nobody needs to store numbers that big".

It's called "scientific notation" for a reason - I'd expect that any
TIFF file that contains data pushing the limits on the range of double
would contain scientific data. I can assure you that TIFF is at least
occasionally used to store floating point scientific data - I've seen it
used to store MODIS (the NASA project I work on) radiance data, for
instance.

The larger a number is, the fewer are the contexts in which it's likely
to come up, and even I have a great deal of trouble coming up with a
plausible example of a reason to store a number that big. The most
likely candidate I can think of for such numbers is numerical modeling
of black hole collisions - but the designers of such simulations would
presumable go to a great deal of trouble to design them so they don't
have to involve numbers that big - in order to ensure that intermediate
calculations neither overflow nor underflow nor suffer a large loss of
significance.

But if it's to be a generic limit that applies to all TIFF readers, I
don't see how he can justify assuming that no one will ever use more
than a tiny fraction of the permitted range of a supported data type.

Thread

Handling numeric types in interpreter luser droog <luser.droog@gmail.com> - 2015-07-13 19:33 -0700
  Re: Handling numeric types in interpreter jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-14 07:31 +0200
  Handling numeric types in interpreter asetofsymbols@gmail.com - 2015-07-14 00:35 -0700
  Re: Handling numeric types in interpreter David Kleinecke <dkleinecke@gmail.com> - 2015-07-14 08:55 -0700
  Re: Handling numeric types in interpreter Bartc <bc@freeuk.com> - 2015-07-15 23:18 +0100
    Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-24 00:21 -0700
      Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-24 08:36 -0700
        Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-24 11:04 -0700
          Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-24 12:25 -0700
            Re: Handling numeric types in interpreter James Kuyper <jameskuyper@verizon.net> - 2015-07-24 22:21 -0400
              Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-25 02:28 -0700
                Re: Handling numeric types in interpreter Bartc <bc@freeuk.com> - 2015-07-25 15:16 +0100
                Re: Handling numeric types in interpreter Richard Damon <Richard@Damon-Family.org> - 2015-07-25 11:03 -0400
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-25 10:05 -0700
              Re: Handling numeric types in interpreter gazelle@shell.xmission.com (Kenny McCormack) - 2015-07-25 12:32 +0000
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-25 06:12 -0700
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-25 10:08 -0700
                Re: Handling numeric types in interpreter ais523 <ais523@nethack4.org> - 2015-07-28 17:50 +0000
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-28 11:52 -0700
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-28 12:25 -0700
                Re: Handling numeric types in interpreter Richard Heathfield <rjh@cpax.org.uk> - 2015-07-28 20:52 +0100
                Re: Handling numeric types in interpreter jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-28 23:01 +0200
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-28 14:44 -0700
                Re: Handling numeric types in interpreter Ian Collins <ian-news@hotmail.com> - 2015-07-29 09:43 +1200
                Re: Handling numeric types in interpreter glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-28 23:10 +0000
                Re: Handling numeric types in interpreter Ian Collins <ian-news@hotmail.com> - 2015-07-29 12:04 +1200
                Re: Handling numeric types in interpreter Melzzzzz <mel@zzzzz.com> - 2015-07-29 02:39 +0200
                Re: Handling numeric types in interpreter jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-29 12:04 +0200
                Re: Handling numeric types in interpreter glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-29 14:58 +0000
                Re: Handling numeric types in interpreter jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-29 14:14 +0200
                Re: Handling numeric types in interpreter Bartc <bc@freeuk.com> - 2015-07-29 13:29 +0100
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-29 08:48 -0700
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-29 08:45 -0700
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-28 16:28 -0700
                Re: Handling numeric types in interpreter jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-29 12:02 +0200
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-29 08:51 -0700
                Re: Handling numeric types in interpreter jacobnavia <jacob@jacob.remcomp.fr> - 2015-07-29 18:35 +0200
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-29 10:47 -0700
                Re: Handling numeric types in interpreter Robert Wessel <robertwessel2@yahoo.com> - 2015-07-25 15:46 -0500
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-25 14:08 -0700
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-25 15:42 -0700
                Re: Handling numeric types in interpreter Robert Wessel <robertwessel2@yahoo.com> - 2015-07-26 00:31 -0500
                Re: Handling numeric types in interpreter James Kuyper <jameskuyper@verizon.net> - 2015-07-25 17:48 -0400
                Re: Handling numeric types in interpreter Robert Wessel <robertwessel2@yahoo.com> - 2015-07-25 17:31 -0500
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-25 15:57 -0700
                Re: Handling numeric types in interpreter Bartc <bc@freeuk.com> - 2015-07-26 01:07 +0100
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-25 17:26 -0700
                Re: Handling numeric types in interpreter Richard Damon <Richard@Damon-Family.org> - 2015-07-25 22:25 -0400
                Re: Handling numeric types in interpreter James Kuyper <jameskuyper@verizon.net> - 2015-07-25 19:04 -0400
                Re: Handling numeric types in interpreter Robert Wessel <robertwessel2@yahoo.com> - 2015-07-26 00:23 -0500
                Re: Handling numeric types in interpreter James Kuyper <jameskuyper@verizon.net> - 2015-07-26 08:24 -0400
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-26 06:36 -0700
                Re: Handling numeric types in interpreter Robert Wessel <robertwessel2@yahoo.com> - 2015-07-26 16:30 -0500
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-26 15:42 -0700
                Re: Handling numeric types in interpreter Robert Wessel <robertwessel2@yahoo.com> - 2015-07-26 16:28 -0500
                Re: Handling numeric types in interpreter James Kuyper <jameskuyper@verizon.net> - 2015-07-26 18:57 -0400
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-26 16:20 -0700
                Re: Handling numeric types in interpreter Keith Thompson <kst-u@mib.org> - 2015-07-25 15:58 -0700
              Re: Handling numeric types in interpreter James Kuyper <jameskuyper@verizon.net> - 2015-07-25 12:56 -0400
                Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-25 14:18 -0700
      Re: Handling numeric types in interpreter glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-24 18:06 +0000
        Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-24 11:16 -0700
          Re: Handling numeric types in interpreter glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-07-24 23:06 +0000
            Re: Handling numeric types in interpreter Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-07-24 16:21 -0700
  Re: Handling numeric types in interpreter Michael Angelo Ravera <maravera@prodigy.net> - 2015-07-15 19:13 -0700
    Re: Handling numeric types in interpreter luser droog <luser.droog@gmail.com> - 2015-07-23 08:36 -0700

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