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Groups > comp.lang.c > #164132
| From | Kaz Kylheku <480-992-1380@kylheku.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Can this program be improved? |
| Date | 2021-12-30 21:04 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <20211230124827.649@kylheku.com> (permalink) |
| References | (4 earlier) <87sfub2g2t.fsf@nosuchdomain.example.com> <sqiprq$1kk$1@dont-email.me> <Cy6zJ.242630$IW4.143221@fx48.iad> <20211229162959.990@kylheku.com> <sqk9tn$q5h$1@dont-email.me> |
On 2021-12-30, Bart <bc@freeuk.com> wrote: > On 30/12/2021 00:34, Kaz Kylheku wrote: >> On 2021-12-29, Scott Lurndal <scott@slp53.sl.home> wrote: >>> Bart <bc@freeuk.com> writes: >>>> On 29/12/2021 22:37, Keith Thompson wrote: >>>>> Bart <bc@freeuk.com> writes: >>>>> [...] >>>>>> 3) Double is perfectly suitable for representing monetary amounts, >>>>>> especially in a toy program or for personal use. (I've used it for >>>>>> accounts within a small business.) >>>>> >>>>> In a toy program, sure -- and I'd say *only* in a toy program. >>>>> >>>>> Using floating-point for money risks, at best, rare off-by-one errors, >>>>> such as a computation yielding a result one cent off from the correct >>>>> value. I believe that would be considered unacceptable in any >>>>> real-world financial application. >>>> >>>> Real-world doesn't need to mean dealing with trillions of dollars to the >>>> exact cent. >>> >>> Real-world still uses COBOL for these type of applications. >>> >>>> >>>> Most businesses work with amounts far smaller. Then I believe the >>>> precision of float64 is enough to emulate the needed rounding methods. >>> >>> Why bother with the error-prone "needed rounding methods". Use uint64_t >>> and denominate in mills. >> >> This common intution is incorrect. Financial systems sometimews need to >> calculate fractional amounts, like a 15.03% tax or whatever. >> >> And in those situations, you may be required to implement the required >> rounding rules: what to do when some fractional result lands halfway >> between two pennies: which one does it go to. >> >> You cannot get away from rounding issues just because you used an >> integer representation for mills or penies. > > The problem isn't the recommended rounding method, it's repeatability. > > With floating point, an intermediate result might end in .4999999993 or > in .5000000007. If the rule is that up to exactly 0.5 rounds down, and > anything beyond rounds up, then it can go either way. This is fairly straightforward, actually. Suppose we are workign with dollars and cents, and have a $0.0049999993 or $0.005000000007 result. We do not just look at the 4 or 5 digit we look at (at least) one more digit, and round that off first: $0.0049... -> $0.0050 -> $0.005 $0.0050... -> $0.0050 -> $0.005 Now that we have our mill (tenth of a cent) denomination rounded off using conventional arithmetic rounding, we then look at the tenth of a cent digit and round to the cent. Here we can use a specific rounding rule like Banker's for instance, if we are so inclined: $0.005 -> $0.00 // digit before 5 is 0, which is even, so down This could be done with character processing: format the floating point number to a certain number of fixed digits after the decimal point, just letting sprintf (or whatever function) doing its built-in rounding. Then, using the resulting decimal, implement the exact pencil-and-paper rounding method. Or it can all be done with just floating-point calculations. The key point is that both of the original numbers $0.0049999993 and $0.005000000007 are understood to be floating-point approximations representing precisely half a cent, and with a little care we can get the rounding to work accordingly: we can get that half a cent value first, and then implement the required rounding to the cent.
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Can this program be improved? Manu Raju <MR@invalid.invalid> - 2021-12-25 01:00 +0000
Re: Can this program be improved? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2021-12-24 21:44 -0800
Re: Can this program be improved? David Brown <david.brown@hesbynett.no> - 2021-12-25 12:56 +0100
Re: Can this program be improved? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-25 11:13 -0800
Re: Can this program be improved? Manfred <noname@add.invalid> - 2021-12-25 23:50 +0100
Re: Can this program be improved? Manu Raju <MR@invalid.invalid> - 2021-12-26 18:52 +0000
Re: Can this program be improved? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2021-12-26 19:22 +0000
Re: Can this program be improved? Manu Raju <MR@invalid.invalid> - 2021-12-26 21:30 +0000
Re: Can this program be improved? Bart <bc@freeuk.com> - 2021-12-26 22:02 +0000
Re: Can this program be improved? Richard Damon <Richard@Damon-Family.org> - 2021-12-26 18:24 -0500
Re: Can this program be improved? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2021-12-27 00:47 +0000
Re: Can this program be improved? Guillaume <message@bottle.org> - 2021-12-29 17:52 +0100
Re: Can this program be improved? Bart <bc@freeuk.com> - 2021-12-29 17:49 +0000
Re: Can this program be improved? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2021-12-29 11:33 -0800
Re: Can this program be improved? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-12-29 22:45 -0500
Re: Can this program be improved? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2021-12-30 00:35 -0800
Re: Can this program be improved? David Brown <david.brown@hesbynett.no> - 2021-12-30 10:19 +0100
Re: Can this program be improved? Bart <bc@freeuk.com> - 2022-01-01 18:19 +0000
Re: Can this program be improved? Bart <bc@freeuk.com> - 2022-01-01 19:33 +0000
Re: Can this program be improved? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-29 14:37 -0800
Re: Can this program be improved? Bart <bc@freeuk.com> - 2021-12-29 23:09 +0000
Re: Can this program be improved? scott@slp53.sl.home (Scott Lurndal) - 2021-12-29 23:54 +0000
Re: Can this program be improved? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-29 16:11 -0800
Re: Can this program be improved? Kaz Kylheku <480-992-1380@kylheku.com> - 2021-12-30 00:34 +0000
Re: Can this program be improved? Bart <bc@freeuk.com> - 2021-12-30 12:49 +0000
Re: Can this program be improved? Kaz Kylheku <480-992-1380@kylheku.com> - 2021-12-30 21:04 +0000
Re: Can this program be improved? Bart <bc@freeuk.com> - 2021-12-31 02:13 +0000
Re: Can this program be improved? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-29 16:09 -0800
Re: Can this program be improved? Kaz Kylheku <480-992-1380@kylheku.com> - 2021-12-30 00:59 +0000
Re: Can this program be improved? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-29 17:48 -0800
Re: Can this program be improved? Kaz Kylheku <480-992-1380@kylheku.com> - 2021-12-30 20:47 +0000
Re: Can this program be improved? Bart <bc@freeuk.com> - 2021-12-30 01:06 +0000
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-12-30 04:48 -0800
Re: Can this program be improved? Manfred <noname@add.invalid> - 2021-12-30 18:16 +0100
Re: Can this program be improved? Bart <bc@freeuk.com> - 2021-12-31 02:20 +0000
Re: Can this program be improved? Manfred <noname@add.invalid> - 2021-12-31 18:25 +0100
Re: Can this program be improved? James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-12-31 18:13 -0500
Re: Can this program be improved? Bart <bc@freeuk.com> - 2021-12-31 23:59 +0000
Re: Can this program be improved? "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-12-31 16:20 -0800
Re: Can this program be improved? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-31 16:35 -0800
Re: Can this program be improved? Bart <bc@freeuk.com> - 2022-01-01 00:53 +0000
Re: Can this program be improved? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-31 20:22 -0800
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-12-31 22:04 -0800
Re: Can this program be improved? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-01 14:59 -0800
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-02 17:22 -0800
Re: Can this program be improved? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-02 20:49 -0800
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-03 03:09 -0800
Re: Can this program be improved? scott@slp53.sl.home (Scott Lurndal) - 2022-01-03 16:22 +0000
Re: Can this program be improved? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-03 14:42 -0800
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-03 14:52 -0800
Re: Can this program be improved? gazelle@shell.xmission.com (Kenny McCormack) - 2022-01-03 22:58 +0000
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-04 04:27 -0800
Re: Can this program be improved? gazelle@shell.xmission.com (Kenny McCormack) - 2022-01-04 13:39 +0000
Re: Can this program be improved? David Brown <david.brown@hesbynett.no> - 2022-01-04 00:18 +0100
Re: Can this program be improved? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-03 15:24 -0800
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-03 15:43 -0800
Re: Can this program be improved? Öö Tiib <ootiib@hot.ee> - 2022-01-03 21:19 -0800
Re: Can this program be improved? Mateusz Viste <mateusz@xyz.invalid> - 2022-01-04 09:23 +0100
Re: Can this program be improved? Guillaume <message@bottle.org> - 2022-01-04 18:18 +0100
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-04 10:35 -0800
Re: Can this program be improved? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-04 14:07 -0800
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-04 15:11 -0800
Re: Can this program be improved? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-04 15:47 -0800
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-04 18:30 -0800
Re: Can this program be improved? scott@slp53.sl.home (Scott Lurndal) - 2022-01-04 23:46 +0000
Re: Can this program be improved? Bart <bc@freeuk.com> - 2022-01-04 18:41 +0000
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-04 10:52 -0800
Re: Can this program be improved? scott@slp53.sl.home (Scott Lurndal) - 2022-01-04 19:00 +0000
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-04 11:15 -0800
Re: Can this program be improved? Guillaume <message@bottle.org> - 2022-01-04 21:57 +0100
Re: Can this program be improved? Bart <bc@freeuk.com> - 2022-01-04 21:02 +0000
Re: Can this program be improved? scott@slp53.sl.home (Scott Lurndal) - 2022-01-04 21:38 +0000
Re: Can this program be improved? Manfred <noname@add.invalid> - 2022-01-04 23:01 +0100
Re: Can this program be improved? David Brown <david.brown@hesbynett.no> - 2022-01-04 09:31 +0100
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-04 01:30 -0800
Re: Can this program be improved? David Brown <david.brown@hesbynett.no> - 2022-01-04 14:55 +0100
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-04 06:21 -0800
Re: Can this program be improved? David Brown <david.brown@hesbynett.no> - 2022-01-04 16:49 +0100
Re: Can this program be improved? gazelle@shell.xmission.com (Kenny McCormack) - 2022-01-04 15:56 +0000
Re: Can this program be improved? gazelle@shell.xmission.com (Kenny McCormack) - 2022-01-04 15:03 +0000
Re: Can this program be improved? gazelle@shell.xmission.com (Kenny McCormack) - 2022-01-03 22:54 +0000
Re: Can this program be improved? Mateusz Viste <mateusz@xyz.invalid> - 2022-01-03 09:22 +0100
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-03 03:30 -0800
Re: Can this program be improved? David Brown <david.brown@hesbynett.no> - 2022-01-03 17:22 +0100
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-03 08:48 -0800
Re: Can this program be improved? Mateusz Viste <mateusz@xyz.invalid> - 2022-01-03 18:42 +0100
Re: Can this program be improved? Bart <bc@freeuk.com> - 2022-01-03 17:59 +0000
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-03 11:09 -0800
Re: Can this program be improved? Mateusz Viste <mateusz@xyz.invalid> - 2022-01-03 20:32 +0100
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-03 11:58 -0800
Re: Can this program be improved? scott@slp53.sl.home (Scott Lurndal) - 2022-01-03 18:13 +0000
Re: Can this program be improved? gazelle@shell.xmission.com (Kenny McCormack) - 2022-01-03 20:05 +0000
Re: Can this program be improved? Bart <bc@freeuk.com> - 2022-01-01 16:53 +0000
Re: Can this program be improved? Kaz Kylheku <480-992-1380@kylheku.com> - 2021-12-30 00:29 +0000
Re: Can this program be improved? Bart <bc@freeuk.com> - 2021-12-25 12:47 +0000
Re: Can this program be improved? Manu Raju <MR@invalid.invalid> - 2021-12-26 18:56 +0000
Re: Can this program be improved? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2021-12-25 17:38 +0000
Re: Can this program be improved? Öö Tiib <ootiib@hot.ee> - 2021-12-25 10:58 -0800
Re: Can this program be improved? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2021-12-25 19:16 +0000
Re: Can this program be improved? Öö Tiib <ootiib@hot.ee> - 2021-12-25 11:25 -0800
Re: Can this program be improved? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-12-25 15:01 -0800
Re: Can this program be improved? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2021-12-25 23:09 +0000
Re: Can this program be improved? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-12-25 20:56 -0800
Re: Can this program be improved? scott@slp53.sl.home (Scott Lurndal) - 2021-12-25 19:30 +0000
Re: Can this program be improved? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-25 15:50 -0800
Re: Can this program be improved? Manu Raju <MR@invalid.invalid> - 2021-12-26 19:02 +0000
Re: Can this program be improved? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2021-12-25 11:53 -0800
Re: Can this program be improved? Manu Raju <MR@invalid.invalid> - 2021-12-26 19:00 +0000
Re: Can this program be improved? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-12-25 11:22 -0800
Re: Can this program be improved? Manu Raju <MR@invalid.invalid> - 2021-12-26 19:01 +0000
Re: Can this program be improved? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2021-12-25 13:27 -0800
Re: Can this program be improved? Andrey Tarasevich <andreytarasevich@hotmail.com> - 2021-12-25 16:06 -0800
Re: Can this program be improved? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2021-12-29 15:21 +0000
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