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Groups > comp.lang.c > #403725
| From | scott@slp53.sl.home (Scott Lurndal) |
|---|---|
| Subject | Re: .5 against 0.5f |
| Newsgroups | comp.lang.c |
| References | <11bpvs7$1e6kc$2@dont-email.me> <11bqnvh$1np7s$1@dont-email.me> <Ue6ES.2265$y_V1.1859@fx12.iad> <20261027125914.162@kylheku.com> <11br9at$1uh9q$1@kst.eternal-september.org> |
| Message-ID | <FjpES.74628$_pxc.26774@fx17.iad> (permalink) |
| Organization | UsenetServer - www.usenetserver.com |
| Date | 2026-10-28 16:23 +0000 |
Keith Thompson <Keith.S.Thompson+u@gmail.com> writes: >Kaz Kylheku <046-301-5902@kylheku.com> writes: >> On 2026-10-27, Scott Lurndal <scott@slp53.sl.home> wrote: >>> I ordered a couple of blu-rays from amazon last week, and the >>> confirmation email had the following for the total price: >>> >>> Total >>> 75.71000000000001 USD > >[...] > >> FP is fine for pricing: look at how ridiculously close to 75.71 >> the above approximation is. You just have to make sure never to >> let enough error accumulate so that an intermediate value >> is suddenly closer to the wrong penny value than the right one. > >And how do you do that? > >> (Actually you don't even want to get anywhere near that level >> of error.) > >An arbitrarily small error can result in an ambiguity. If you >calculate a result that should, mathematically, be very close to >75.715, it could round either to 75.71 or to 75.72. > >I presume there are financial regulations that specify exactly how >these calculations are to be performed. I have no idea what those >regulations say, but anyone writing financial code had better know >about the requirements and implement them correctly. There are. And they explicitly forbid using binary floating point representations. Typically they use scaled fixed point 64-bit integers in modern code.
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.5 against 0.5f fir <profesor.fir@gmail.com> - 2026-10-27 11:53 +0100
Re: .5 against 0.5f "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu> - 2026-10-27 17:45 +0000
Re: .5 against 0.5f fir <profesor.fir@gmail.com> - 2026-10-27 18:50 +0100
Re: .5 against 0.5f "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu> - 2026-10-27 19:01 +0000
Re: .5 against 0.5f fir <profesor.fir@gmail.com> - 2026-10-27 20:15 +0100
Re: .5 against 0.5f "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu> - 2026-10-27 19:54 +0000
Re: .5 against 0.5f "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-10-27 13:10 -0700
Re: .5 against 0.5f steve g <Sgonedes1977@gmail.com> - 2026-10-28 02:20 -0400
Re: .5 against 0.5f David Brown <david.brown@hesbynett.no> - 2026-10-27 21:35 +0100
Re: .5 against 0.5f James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-10-27 18:00 -0400
Re: .5 against 0.5f "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu> - 2026-10-27 22:15 +0000
Re: .5 against 0.5f Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-28 06:54 -0700
Re: .5 against 0.5f fir <profesor.fir@gmail.com> - 2026-10-27 21:57 +0100
Re: .5 against 0.5f "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-10-27 14:18 -0700
Re: .5 against 0.5f steve g <Sgonedes1977@gmail.com> - 2026-10-28 02:19 -0400
Re: .5 against 0.5f Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-10-28 21:54 +0000
Re: .5 against 0.5f "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-10-28 14:58 -0700
Re: .5 against 0.5f steve g <Sgonedes1977@gmail.com> - 2026-10-28 02:11 -0400
Re: .5 against 0.5f Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-27 23:21 -0700
Re: .5 against 0.5f scott@slp53.sl.home (Scott Lurndal) - 2026-10-27 18:40 +0000
Re: .5 against 0.5f Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-27 12:29 -0700
Re: .5 against 0.5f "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-10-27 13:11 -0700
Re: .5 against 0.5f "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-10-27 13:25 -0700
Re: .5 against 0.5f Michael S <already5chosen@yahoo.com> - 2026-10-27 21:43 +0200
Re: .5 against 0.5f Michael S <already5chosen@yahoo.com> - 2026-10-27 22:05 +0200
Re: .5 against 0.5f Michael S <already5chosen@yahoo.com> - 2026-10-27 22:51 +0200
Re: .5 against 0.5f Kaz Kylheku <046-301-5902@kylheku.com> - 2026-10-27 20:05 +0000
Re: .5 against 0.5f bartc <bc@freeuk.com> - 2026-10-27 21:03 +0000
Re: .5 against 0.5f Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-27 15:41 -0700
Re: .5 against 0.5f scott@slp53.sl.home (Scott Lurndal) - 2026-10-28 16:23 +0000
Re: .5 against 0.5f steve g <Sgonedes1977@gmail.com> - 2026-10-28 02:25 -0400
Re: .5 against 0.5f makendo <makendo@makendo.invalid> - 2026-10-29 18:04 +0800
Re: .5 against 0.5f Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-29 05:01 -0700
Re: .5 against 0.5f David Brown <david.brown@hesbynett.no> - 2026-10-29 13:55 +0100
Re: .5 against 0.5f bartc <bc@freeuk.com> - 2026-10-29 14:32 +0000
Re: .5 against 0.5f Kaz Kylheku <046-301-5902@kylheku.com> - 2026-10-27 19:58 +0000
Re: .5 against 0.5f James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-10-27 17:43 -0400
Re: .5 against 0.5f James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-10-27 18:06 -0400
Re: .5 against 0.5f Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-10-28 00:49 +0000
Re: .5 against 0.5f Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-27 18:23 -0700
Re: .5 against 0.5f Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-28 16:38 +0100
Re: .5 against 0.5f Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-28 13:27 -0700
Re: .5 against 0.5f Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-29 00:08 +0100
Re: .5 against 0.5f Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-28 16:56 -0700
Re: .5 against 0.5f Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-29 18:55 +0100
Re: .5 against 0.5f David Brown <david.brown@hesbynett.no> - 2026-10-29 09:30 +0100
Re: .5 against 0.5f Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-29 04:54 -0700
Re: .5 against 0.5f Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-29 19:57 +0100
Re: .5 against 0.5f David Brown <david.brown@hesbynett.no> - 2026-10-29 20:56 +0100
Re: .5 against 0.5f Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-29 23:06 +0100
Re: .5 against 0.5f Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-29 13:39 -0700
Re: .5 against 0.5f James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-10-27 21:41 -0400
Re: .5 against 0.5f David Brown <david.brown@hesbynett.no> - 2026-10-28 08:45 +0100
Re: .5 against 0.5f "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu> - 2026-10-28 01:50 +0000
Re: .5 against 0.5f fir <profesor.fir@gmail.com> - 2026-10-28 07:32 +0100
Re: .5 against 0.5f fir <profesor.fir@gmail.com> - 2026-10-28 07:51 +0100
Re: .5 against 0.5f fir <profesor.fir@gmail.com> - 2026-10-28 07:55 +0100
Re: .5 against 0.5f "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu> - 2026-10-28 16:27 +0000
Re: .5 against 0.5f David Brown <david.brown@hesbynett.no> - 2026-10-28 17:44 +0100
Re: .5 against 0.5f "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu> - 2026-10-28 16:22 +0000
Re: .5 against 0.5f fir <profesor.fir@gmail.com> - 2026-10-28 19:15 +0100
Re: .5 against 0.5f fir <profesor.fir@gmail.com> - 2026-10-28 19:47 +0100
Re: .5 against 0.5f "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu> - 2026-10-28 19:10 +0000
Re: .5 against 0.5f Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-28 13:31 -0700
Re: .5 against 0.5f "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu> - 2026-10-28 22:44 +0000
Re: .5 against 0.5f Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-29 00:27 +0100
Re: .5 against 0.5f Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-28 16:39 -0700
Re: .5 against 0.5f "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu> - 2026-10-29 00:22 +0000
Re: .5 against 0.5f Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-28 17:59 -0700
Re: .5 against 0.5f "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu> - 2026-10-29 01:50 +0000
Re: .5 against 0.5f David Brown <david.brown@hesbynett.no> - 2026-10-29 10:45 +0100
Re: .5 against 0.5f cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-29 14:56 +0000
Re: .5 against 0.5f "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu> - 2026-10-29 16:34 +0000
Re: .5 against 0.5f James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-10-29 11:56 -0400
Re: .5 against 0.5f "Steven G. Kargl" <sgk@REMOVEtroutmask.apl.washington.edu> - 2026-10-29 17:57 +0000
Re: .5 against 0.5f cross@spitfire.i.gajendra.net (Dan Cross) - 2026-10-29 19:49 +0000
Re: .5 against 0.5f Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-29 22:55 +0100
Re: .5 against 0.5f Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-10-29 17:58 +0100
Re: .5 against 0.5f David Brown <david.brown@hesbynett.no> - 2026-10-28 08:39 +0100
Re: .5 against 0.5f Michael S <already5chosen@yahoo.com> - 2026-10-28 22:25 +0200
Re: .5 against 0.5f David Brown <david.brown@hesbynett.no> - 2026-10-29 10:48 +0100
Re: .5 against 0.5f Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-29 04:59 -0700
Re: .5 against 0.5f Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-28 14:26 -0700
Re: .5 against 0.5f Michael S <already5chosen@yahoo.com> - 2026-10-29 00:12 +0200
Re: .5 against 0.5f bartc <bc@freeuk.com> - 2026-10-28 22:33 +0000
Re: .5 against 0.5f David Brown <david.brown@hesbynett.no> - 2026-10-29 11:01 +0100
Re: .5 against 0.5f Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-28 16:05 -0700
Re: .5 against 0.5f David Brown <david.brown@hesbynett.no> - 2026-10-29 10:59 +0100
Re: .5 against 0.5f "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-10-28 14:34 -0700
Re: .5 against 0.5f David Brown <david.brown@hesbynett.no> - 2026-10-29 11:06 +0100
Re: .5 against 0.5f tTh <tth@none.invalid> - 2026-10-28 15:08 +0100
Re: .5 against 0.5f Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-28 07:49 -0700
Re: .5 against 0.5f "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-10-28 14:36 -0700
Re: .5 against 0.5f Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-27 15:53 -0700
Re: .5 against 0.5f James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-10-27 21:55 -0400
Re: .5 against 0.5f Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-27 19:02 -0700
Re: .5 against 0.5f David Brown <david.brown@hesbynett.no> - 2026-10-28 08:56 +0100
Re: .5 against 0.5f Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-28 08:01 -0700
Re: .5 against 0.5f "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-10-27 13:08 -0700
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