[squeak-dev] Rounding floats
cunningham.cb at gmail.com
Tue Jul 19 14:46:40 UTC 2016
On Mon, Jul 18, 2016 at 5:26 PM, Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com> wrote:
> Hi Tim,
> you can't round float that easily, they are not multiple of 1/5.
> But you can round their printed decimal representation.
> That's fair because this is what you want: print the damn float
> 292.37 printShowingMaxDecimalPlaces: 1
> Technically, 2924*0.1 and 2924/10.0 differ.
> The second one is guaranteed to be the closest float to (2924/10) because
> there's only one inexact operation involved (the division).
> The first one, not so, it's 2924 * (1/10.0), two inexact operations
> Remember, 1/10 = 0.1 is false...
> That's why roundTo: is failing: it uses the second formula.
> Otherwise, of course, you would use ScaledDecimals or Fractions...
> 239.37 roundTo: 0.1s.
> (239.37 roundTo: 1/10) asFloat.
> But you want to print rounded, so just print rounded, don't bother with
or FixedDecimals (if you want to load that package).
> 239.37 asFixedDecimal: 1 "==> 239.4 "
> 2016-07-19 1:20 GMT+02:00 tim Rowledge <tim at rowledge.org>:
>> I know that it’s a hard thing to deal with floating point numbers around
>> the fiddly edges, but are we really unable to do a decent job of rounding
>> floats to reasonable numbers of decimal places? This can’t be a rare thing
>> to need to do.
>> For example, I’m reading temperature values for various places from the
>> openweathermap.org site and many of them are specified to 2dp, which
>> seems a bit optimistic for a weather site. But if I try, for example
>> 292.37 roundTo: 0.1
>> I get the very unhelpful 292.40000…00003 (with too many 0s to count by
>> eye). I understand that one option is to use formatted printing of the
>> number but that doesn’t seem practical for this usage right now.
>> So, numerics aficionados, can we do any better than the sensible seeming
>> but unsuccessful code in Number>>roundTo: ?
>> tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
>> Ubi dubium ibi libertas
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