Buglet in ES3 Math.round description

# Mike Cowlishaw (17 years ago)

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

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

Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU

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

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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





Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU

# Mike Cowlishaw (17 years ago)

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:

Mike

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

Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU

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

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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





Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU