XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (528 page)

If the argument value is an
xs:double
or
xs:float
greater than -1.0 but less than zero it will be rounded up to negative zero. For most practical purposes, negative zero and positive zero are indistinguishable, but dividing a number by negative zero produces negative infinity, while dividing by positive zero produces positive infinity.

Examples

Expression	Result
ceiling(1.0)	xs:decimal 1.0, displayed as 1
ceiling(1.6)	xs:decimal 2.0, displayed as 2
ceiling(17 div 3)	xs:decimal 6.0, displayed as 6
ceiling(-3.0)	xs:decimal −3.0, displayed as -3
ceiling(-8.2e0)	xs:double −8.0e0, displayed as -8
ceiling(number(‘xxx’))	xs:double NaN, displayed as NaN
ceiling(-0.5e0)	xs:double −0.0e0, displayed as -0