openerp-india team mailing list archive

[Raphaël Valyi - http://www.akretion.com <882036@xxxxxxxxxxxxxxxxxx>]

Dear OpenERP experts,

I don't yet what would be wrong with the algorithm we tried to propose here.
But I could see that the topic of rounding floats to the shortest decimal fraction is actually a known topic of numerical calculus.
I've found some sources claiming the best algorithm would be the Dybvig's one:
http://citeseer.ist.psu.edu/viewdoc/download;jsessionid=0CF999B48641E6A3CCDCCCA2D895827B?doi=10.1.1.52.2247&rep=rep1&type=pdf

Also, I've seen that Python 2.7 or 3.1 are doing such rounding to
shortest decimal fraction. I don't know what they are using, but may be
it's reusable somewhat.

I've also found this http://research.swtch.com/2011/07/floating-point-to-decimal-conversion-is.html
and this in response: http://smalltalk.gnu.org/blog/bonzinip/floating-point-decimal-conversion-not-so-easy

Holly shit!

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https://bugs.launchpad.net/bugs/882036

Title:
  Incorrect float rounding when setting float field with too high
  precision

Status in OpenERP GTK Client:
  Confirmed
Status in OpenERP Server:
  Confirmed
Status in OpenERP Server 6.0 series:
  Confirmed

Bug description:
  Concerns 6.0 and trunk.
  If you define a precision of 0.01, the rounding of 0.125 must be 0.13 and not 0.12. The error is in the call of the format string "%.2f"%val which introduces a mathematical error. The round function must be called to apply the correct rounding before formatting the string. It should be:
  "%.2f"%round(val*100)/100
  Fix class digits_change of class float in the server. BUT fix also the gtk client AND web client as they all have that error (I let you find the right line)

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