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8.7 Floating Point different than 8.6.1

Added by Anonymous over 18 years ago

Legacy ID: #3603412 Legacy Poster: Francis Upton (francisu)

I just upgraded to 8.7 from 8.6.1. In my tests some statements that cast some text values to a float (after checking castable as float). Here are the diff results: 1169c1169 < <G3905>22426.051</G3905> --- > <G3905>22426.05</G3905> 1504c1504 < <G5505>279.04998</G5505> --- > <G5505>279.05</G5505> 1512c1512 < <G5514>279.14002</G5514> --- > <G5514>279.14</G5514> 1777c1777 < <G3908>340.07998</G3908> --- > <G3908>340.08</G3908> 1792c1792 < <G3926>340.01502</G3926> --- > <G3926>340.015</G3926> The top value is the actual output, the bottom value is the input text value. Saxon 8.6.1 correctly had both values match. Thanks, Francis


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RE: 8.7 Floating Point different than 8.6.1 - Added by Anonymous over 18 years ago

Legacy ID: #3603766 Legacy Poster: Michael Kay (mhkay)

Please see http://sourceforge.net/tracker/index.php?func=detail&amp;aid=1439685&amp;group_id=29872&amp;atid=397617 There will always be several different strings that convert to the same floating point number, so when you convert back to a string there can never be a guarantee that you will get the string you started with, though it should always be "equivalent". If you care about precision, I would strongly suggest using double rather than float. Having said that, the new conversion routine introduced in 8.7 has not proved to be a success.

RE: 8.7 Floating Point different than 8.6.1 - Added by Anonymous over 18 years ago

Legacy ID: #3605065 Legacy Poster: Francis Upton (francisu)

Thanks Mike. This use of FP is for simple decimal monetary amounts which don't exceed 2 decimal places, so one hopes that the conversion would be fairly precise. When using relatively small quantities (such as this), is the use of "double" an improvement over "float"? Should I never use float? I took your file and that fixed the problem.

RE: 8.7 Floating Point different than 8.6.1 - Added by Anonymous over 18 years ago

Legacy ID: #3605096 Legacy Poster: Michael Kay (mhkay)

For monetary amounts I would recommend decimal. Float might have enough digits for your numbers, but arithmetic rounding errors accumulate very rapidly in computations, for example if you take an average or a total of a set of numbers.

RE: 8.7 Floating Point different than 8.6.1 - Added by Anonymous over 18 years ago

Legacy ID: #3605103 Legacy Poster: Michael Kay (mhkay)

And yes, my advice is never to use float. I really can't see the need for 32-bit floating point numbers in the 21st century.

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