Thanx for the precise information. I was coming from a perspective of safe implementation, when dealing with variables, you might not always know whether the values to be compared will fall under the exact floating point representation, so the safe way to go might always be to use the < 1.0e-5 method or go with library functions. You see any problem with this too ?
Programmers should realize their critical importance and responsibility in a world gone digital. They are in many ways similar to the priests and monks of Europe's Dark Ages; they are the only ones with the training and insight to read and interpret the "scripture" of this age. On Fri, Jan 7, 2011 at 4:15 AM, Dave <dave_and_da...@juno.com> wrote: > I don't think your example with == would ever fail. According to the > IEEE floating point standard, integers within the dynamic range of the > number type must be represented exactly and must compare as equal. > > Furthermore, the four basic operations on integers within the dynamic > range of the floating point number type that have integer results > within that dynamic range must be exact. Thus, 25.0 - 5.0, 13.0 + 7.0, > 4.0 * 5.0, and 60.0 / 3.0 all must equal 20.0 exactly. > > Where you run into trouble is when the numbers in question cannot be > represented exactly in the finite precision floating point format -- > something like this: > > double d1 = 6.1; > double d2 = 11.6; > double d3 = 17.7; > > assert(d1 + d2 == d3); // might fail, and Wrong way to do it !! > > And your "correct and recommended way" is missing an absolute value: > > assert(abs(d1 + d2 - d3) < 1.0e-5); // given you assume precision of > 1e-5 is the correct and recommended way. > > Dave > > On Jan 6, 4:19 pm, Avi Dullu <avi.du...@gmail.com> wrote: > > Just to mention, floating point numbers r always compared *for equality* > > like > > > > double d1 = 90.0; > > double d2 = 90.0; > > > > assert(d1 == d2); // might fail, and Wrong way to do !! > > > > assert(d1 - d2 < 1e-5); // given u assume precision of 1e-5, is the > correct > > and recommended way. > > > > Programmers should realize their critical importance and responsibility > in a > > world gone digital. They are in many ways similar to the priests and > monks > > of Europe's Dark Ages; they are the only ones with the training and > insight > > to read and interpret the "scripture" of this age. > > > > > > > > On Fri, Jan 7, 2011 at 1:47 AM, juver++ <avpostni...@gmail.com> wrote: > > > Numbers without fractional parts are represented exactly (in a range > > > supported by double). > > > > > -- > > > You received this message because you are subscribed to the Google > Groups > > > "Algorithm Geeks" group. > > > To post to this group, send email to algoge...@googlegroups.com. > > > To unsubscribe from this group, send email to > > > algogeeks+unsubscr...@googlegroups.com<algogeeks%2bunsubscr...@googlegroups.com> > <algogeeks%2bunsubscr...@googlegroups.com> > > > . > > > For more options, visit this group at > > >http://groups.google.com/group/algogeeks?hl=en.- Hide quoted text - > > > > - Show quoted text - > > -- > You received this message because you are subscribed to the Google Groups > "Algorithm Geeks" group. > To post to this group, send email to algoge...@googlegroups.com. > To unsubscribe from this group, send email to > algogeeks+unsubscr...@googlegroups.com<algogeeks%2bunsubscr...@googlegroups.com> > . > For more options, visit this group at > http://groups.google.com/group/algogeeks?hl=en. > > -- You received this message because you are subscribed to the Google Groups "Algorithm Geeks" group. To post to this group, send email to algoge...@googlegroups.com. To unsubscribe from this group, send email to algogeeks+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.
