[ pure-data-Bugs-1996275 ] [change] lets some duplicates thru - Pd-dev

23 Jul 2008


      Bugs item #1996275, was opened at 2008-06-17 18:38
Message generated for change (Comment added) made by zmoelnig
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Category: puredata
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Hans-Christoph Steiner (eighthave)
Assigned to: Nobody/Anonymous (nobody)
Summary: [change] lets some duplicates thru
Initial Comment:
Sometimes some duplicates get through [change] since it is doing a != for the comparison.  Instead it should do a  comparison with a set precision, something like this:
http://howto.wikia.com/wiki/Howto_compare_float_numbers_in_the_C_programming...
//compares if the float f1 is equal with f2 and returns 1 if true and 0 if false
 int compare_float(float f1, float f2)
 {
  float precision = 0.00001;
  if (((f1 - precision) < f2) && 
      ((f1 + precision) > f2))
   {
    return 1;
   }
  else
   {
    return 0;
   }
 }
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Comment By: IOhannes m zmlnig (zmoelnig)
Date: 2008-07-23 16:23
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ah i see, but this is a misunderstanding on your side.
Pd uses _full_ precision of floats. however it will only display (and
save) a number with a limited precision.
i don't think we should change [change] just because [print] is unable to
show enough precision.
if you use [tgl] instead of [print] you will notice that even more values
look the same :-)
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Comment By: Hans-Christoph Steiner (eighthave)
Date: 2008-07-23 16:08
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Since this comparison is happening in C space, it is done using the full
precision of the float.  But Pd only uses 6 digits of precision, so the
comparison should match that, not what is happening in C space.
Basically, I hooked up a [change]-[print] to some sensor data, and it was
quite common to see the exact same number printed out one after the other.
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Comment By: IOhannes m zmlnig (zmoelnig)
Date: 2008-07-23 09:26
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do you have a practical example that exposes the bug?
in theory you are of course right, but in practice i wonder how this can
be applied to [change].
e.g. if i send "1" and the result of "2/2" to change, i might consider
these two as different enough :-)
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