Re: Why is this happening?

From	Michael S <already5chosen@yahoo.com>
Newsgroups	comp.lang.c
Subject	Re: Why is this happening?
Date	2026-03-31 11:48 +0300
Organization	A noiseless patient Spider
Message-ID	<20260331114830.0000142b@yahoo.com> (permalink)
References	(4 earlier) <87bjg8wrgl.fsf@example.invalid> <CfSxR.24256$eG1.15763@fx33.iad> <20260329115057.00003a47@yahoo.com> <87qzp2uzjc.fsf@example.invalid> <10qf4vi$2u7d8$2@dont-email.me>

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On Mon, 30 Mar 2026 20:37:06 -0400
James Kuyper <jameskuyper@alumni.caltech.edu> wrote:

> On 2026-03-29 16:54, Keith Thompson wrote:
> ...
> > context that doesn't need floating-point.  I'm not sure whether
> > (unsigned long)1e9 is actually guaranteed to yield 1000000000 rather
> > than 999999999.  Maybe it is, but I don't want to waste brain cells
> > proving it.  
> 
> I'll waste my brain cells.
> 
> "When a finite value of decimal floating type is converted to an
> integer type other than bool, the fractional part is discarded (i.e.
> the value is truncated toward zero)." (6.3.2.4p2)
> 
> "For decimal floating literals ... the result is either the nearest
> representable value, or the larger or smaller representable value
> immediately adjacent to the nearest representable value, chosen in an
> implementation-defined manner." (6.4.5.3p4)
> 
> This allows for 1e9 to have a value of exactly 1000000000.0, or
> slightly higher, which converts to unsigned long as 1000000000, or a
> value slightly less than 1000000000.0, which will convert to
> 999999999.
> 

Not when compiler declares itself compliant with IEEE-754 (or IEC
559). By 754, if value is representable exactly then it shall be
chosen, unconditionally. No "adjacent" allowed.

> So you were right - don't use floating point to do what integer types
> are sufficient to do.
> 

You can do what you feel right. And I would do what I feel right.
And I am going to continue to suggest what I think is right to other
people that, like me, care very little about what weird things are
permitted to implementer according to C Standard as long as all
implementations that they are likely to encounter in practice provide
much stronger guarantees.

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Why is this happening? DFS <nospam@dfs.com> - 2026-03-27 00:12 -0400
  Re: Why is this happening? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-03-27 05:46 +0100
    Re: Why is this happening? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-03-27 06:01 +0100
      Re: Why is this happening? DFS <nospam@dfs.com> - 2026-03-27 02:31 -0400
    Re: Why is this happening? Josef Möllers <josef@invalid.invalid> - 2026-03-27 10:15 +0100
      Re: Why is this happening? scott@slp53.sl.home (Scott Lurndal) - 2026-03-27 16:02 +0000
        Re: Why is this happening? Josef Möllers <josef@invalid.invalid> - 2026-03-28 21:58 +0100
          Re: Why is this happening? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-03-29 14:30 +0200
            Re: Why is this happening? scott@slp53.sl.home (Scott Lurndal) - 2026-03-29 18:56 +0000
              Re: Why is this happening? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-03-30 02:00 +0200
            Re: Why is this happening? Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2026-03-30 00:41 +0100
              Re: Why is this happening? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-03-30 09:25 +0200
                Re: Why is this happening? Michael S <already5chosen@yahoo.com> - 2026-03-30 11:23 +0300
                Re: Why is this happening? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-03-30 11:16 +0200
                Re: Why is this happening? Michael S <already5chosen@yahoo.com> - 2026-03-30 13:06 +0300
      Re: Why is this happening? Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-03-28 01:46 +0000
        Re: Why is this happening? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-03-27 20:41 -0700
          Re: Why is this happening? Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-03-28 05:17 +0100
            Re: Why is this happening? David Brown <david.brown@hesbynett.no> - 2026-03-28 10:09 +0100
              Re: Why is this happening? Bart <bc@freeuk.com> - 2026-03-28 11:33 +0000
                Re: Why is this happening? David Brown <david.brown@hesbynett.no> - 2026-03-28 16:35 +0100
                Re: Why is this happening? Richard Harnden <richard.nospam@gmail.invalid> - 2026-03-28 16:56 +0000
                Re: Why is this happening? Richard Harnden <richard.nospam@gmail.invalid> - 2026-03-28 16:58 +0000
                Re: Why is this happening? James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-03-28 19:24 -0400
                Re: Why is this happening? David Brown <david.brown@hesbynett.no> - 2026-03-29 11:33 +0200
                Re: Why is this happening? Richard Harnden <richard.nospam@gmail.invalid> - 2026-03-29 16:30 +0100
                Re: Why is this happening? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-29 10:37 -0700
                Re: Why is this happening? David Brown <david.brown@hesbynett.no> - 2026-03-31 16:20 +0200
                Re: Why is this happening? Richard Harnden <richard.nospam@gmail.invalid> - 2026-03-31 17:19 +0100
                Re: Why is this happening? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-03-29 13:19 -0700
                Re: Why is this happening? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-03-29 13:26 -0700
                Re: Why is this happening? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-03-29 14:14 -0700
                Re: Why is this happening? James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-03-29 20:47 -0400
                Re: Why is this happening? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-03-29 13:57 -0700
                Re: Why is this happening? David Brown <david.brown@hesbynett.no> - 2026-03-31 16:26 +0200
          Re: Why is this happening? scott@slp53.sl.home (Scott Lurndal) - 2026-03-28 15:14 +0000
            Re: Why is this happening? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-03-28 10:18 -0700
              Re: Why is this happening? scott@slp53.sl.home (Scott Lurndal) - 2026-03-29 18:50 +0000
            Re: Why is this happening? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-28 19:12 -0700
              Re: Why is this happening? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-03-28 22:31 -0700
                Re: Why is this happening? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-06 12:11 -0700
                Re: Why is this happening? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-04-06 14:20 -0700
                Re: Why is this happening? Michael S <already5chosen@yahoo.com> - 2026-04-07 02:05 +0300
                Re: Why is this happening? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-04-06 17:42 -0700
                Re: Why is this happening? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-27 20:36 -0700
                Re: Why is this happening? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-04-27 20:58 -0700
              Re: Why is this happening? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-29 14:43 -0700
            Re: Why is this happening? Michael S <already5chosen@yahoo.com> - 2026-03-29 11:50 +0300
              Re: Why is this happening? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-03-29 13:54 -0700
                Re: Why is this happening? Michael S <already5chosen@yahoo.com> - 2026-03-30 02:05 +0300
                Re: Why is this happening? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-03-29 16:22 -0700
                Re: Why is this happening? Michael S <already5chosen@yahoo.com> - 2026-03-30 10:57 +0300
                Re: Why is this happening? James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-03-30 20:37 -0400
                Re: Why is this happening? Michael S <already5chosen@yahoo.com> - 2026-03-31 11:48 +0300
                Re: Why is this happening? James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-03-31 10:51 -0400
                Re: Why is this happening? candycanearter07 <candycanearter07@candycanearter07.nomail.afraid> - 2026-03-31 19:00 +0000
        Re: Why is this happening? Tristan Wibberley <tristan.wibberley+netnews2@alumni.manchester.ac.uk> - 2026-04-03 02:41 +0100

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