Agree with Ian. Solutions are: change expectations, use decimal floating point, or use a base-independent decimal representation. The latter implies scaled integers.
Quick, ugly, and typed on one hand from bed, but here it is: https://play.golang.org/p/fBztRY6qHP0 999000/1000 = 999.0 999050/1000 = 999.1 999100/1000 = 999.1 999150/1000 = 999.2 999200/1000 = 999.2 999250/1000 = 999.3 999300/1000 = 999.3 999350/1000 = 999.4 999400/1000 = 999.4 999450/1000 = 999.5 999500/1000 = 999.5 999550/1000 = 999.6 999600/1000 = 999.6 999650/1000 = 999.7 999700/1000 = 999.7 999750/1000 = 999.8 999800/1000 = 999.8 999850/1000 = 999.9 999900/1000 = 999.9 999950/1000 = 1000.0 -999950/1000 = -1000.0 -999900/1000 = -999.9 -999850/1000 = -999.9 -999800/1000 = -999.8 -999750/1000 = -999.8 -999700/1000 = -999.7 -999650/1000 = -999.7 -999600/1000 = -999.6 -999550/1000 = -999.6 -999500/1000 = -999.5 -999450/1000 = -999.5 -999400/1000 = -999.4 -999350/1000 = -999.4 -999300/1000 = -999.3 -999250/1000 = -999.3 -999200/1000 = -999.2 -999150/1000 = -999.2 -999100/1000 = -999.1 -999050/1000 = -999.1 On Fri, Dec 6, 2019 at 2:31 AM Ian Davis <m...@iandavis.com> wrote: > On Fri, 6 Dec 2019, at 9:25 AM, Christophe Meessen wrote: > > I have noticed that printf performs an apparently inconsistent rounding of > floating point values. > > I divide a big number by 1000 and printf the resulting value with "%.1f". > Here is the code: https://play.golang.org/p/e7dD3c6IHq2 > > > I think you are just seeing the usual problems of floating point > representation. > > You may wonder why 999450/1000=999.45, 999500/1000=999.50 and > 999550/1000=999.55 all format as 999.5. The answer is that the internal > representation of the three results cannot correspond to the mathematical > result you expect. > > This link shows the internal representation of each answer: > https://play.golang.org/p/bBTNCdsAttR > > You can see that 999550/1000 = 999.549999999999954525264911353588104248046875 > which is printed as 999.5 > > > I would expect the rounding rule to be "round away from zero" as defined > here: https://math.stackexchange.com/a/2252888/33796 > In this case 0.5 is rounded to 1 (or 0.05 to 0.1) and -0.5 to -1 (or -0.05 > to -0.1). > > > The strconv and fmt packages use round to even as a rule. Use math.Round > to round away from zero. > > -- Ian > > > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/ee94624c-5485-4daf-98ad-8e59055056dd%40www.fastmail.com > <https://groups.google.com/d/msgid/golang-nuts/ee94624c-5485-4daf-98ad-8e59055056dd%40www.fastmail.com?utm_medium=email&utm_source=footer> > . > -- *Michael T. jonesmichael.jo...@gmail.com <michael.jo...@gmail.com>* -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CALoEmQy%3DMCWgb69GgsZwAv2GT4ar%3DWrdvn212sFK1PfGES1ijw%40mail.gmail.com.
