[GRASS-dev] [GRASS GIS] #2854: results in winGRASS7 32bit vs 64bit: should they be identical?

[GRASS GIS]

#2854: results in winGRASS7 32bit vs 64bit: should they be identical?
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  Reporter:  hellik  |      Owner:  grass-dev@…
      Type:  defect  |     Status:  new
  Priority:  normal  |  Milestone:  7.0.3
 Component:  Raster  |    Version:  svn-releasebranch70
Resolution:          |   Keywords:
       CPU:  x86-64  |   Platform:  MSWindows 7
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Comment (by hellik):

 Replying to [comment:7 neteler]:
 > Replying to [comment:4 hellik]:
 > ...
 >
 > {{{
 > > minimum: -8.14907e-010
 > > maximum: 4.65661e-010
 > > range: 1.28057e-009
 > > mean: -1.12517e-012
 > > mean of absolute values: 1.73591e-012
 > > standard deviation: 0
 > > variance: 0
 > > variation coefficient: -0 %
 > }}}
 >
 >
 > Doesn't this qualify for "basically identical results as much as
 different architectures can achieve"?
 >
 > Some info pages (for who wants to learn more):
 >  * https://msdn.microsoft.com/en-us/library/0b34tf65.aspx
 >  * EPSILON: https://support.microsoft.com/en-us/kb/145889
 >  * https://msdn.microsoft.com/en-
 us/library/windows/desktop/cc308050(v=vs.85).aspx
 >
 > I'm not a CPU precision guru but to me it looks ok. Others?

 I'm also no CPU guru. :-)

 all these tests with 32bit and 64 bit binaries are done on the same
 machine. I find it interesting that some calculations are identical
 between 32 bit and 64 bit (e.g. Slope and aspect), others are not (e.g.
 accumulation by r.watershed or r.Topic).

 though, the diff values are very low and results should be treated as
 identical?

 Maybe adding some notes in the manual (if not already there?)

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Ticket URL: <https://trac.osgeo.org/grass/ticket/2854#comment:8>
GRASS GIS <https://grass.osgeo.org>