Fw: Buglet in ES3 Math.round description

Mike Cowlishaw MFC at uk.ibm.com
Fri Apr 18 12:38:26 PDT 2008


While looking through ES3 for other things, I happened to notice a minor 
fault.  What is the best way to record it so it can be fixed in due 
course?

The error is in an informative note, so is not critical.  It is in section 
15.8.2.15, NOTE 2, which states:

"The value of Math.round(x) is the same as the value of Math.floor(x+0.5), 
except when x is ?0 or is less than 0 but greater than or equal to -0.5; 
for these cases math.round(x) returns ?0, but Math.floor(x+0.5) returns 
+0."

This is not true when x is 0.49999999999999994, which when converted to 
double is the next representable value below 0.5.  In this case, 
Math.floor(x+0.5) would return +1 but Math.round(x) would return +0.

Mike

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Mike Cowlishaw, IBM Fellow
IBM UK (MP8), PO Box 31, Birmingham Road, Warwick, CV34 5JL
mailto:mfc at uk.ibm.com  --  http://www2.hursley.ibm.com/mfcsumm.html





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