- From: Steven Pemberton <steven.pemberton@cwi.nl>
- Date: Wed, 13 Dec 2017 15:32:24 +0100
- To: public-xformsusers@w3.org, "XForms Users Community Group Issue Tracker" <sysbot+tracker@w3.org>, "Steven Pemberton" <steven.pemberton@cwi.nl>

Done. https://www.w3.org/community/xformsusers/wiki/XPath_Expressions_Module#The_power.28.29_Function Steven On Wed, 13 Dec 2017 13:57:51 +0100, Steven Pemberton <steven.pemberton@cwi.nl> wrote: > For power(x, y), we say: > > "Raises the first argument to the power of the second argument, > returning the result. Both arguments may be fractional and negative. If > the calculation does not result in a real number, then NaN is returned." > > and the problem is with the meaning of "if the calculation does not > result in a real number" > > XPath functions says: > https://www.w3.org/TR/xpath-functions/#func-math-pow > > pow($x, $y) > > "If $y is an instance of xs:integer, the result is $x raised to the > power of $y as defined in the [IEEE 754-2008] specification of the pown > function applied to a 64-bit binary floating point value and an integer. > > Otherwise $y is converted to an xs:double by numeric promotion, and the > result is the value of $x raised to the power of $y as defined in the > [IEEE 754-2008] specification of the pow function applied to two 64-bit > binary floating point values." > > IEEE 754 says: > > "For the pown function (integral exponents only): > pown(x, 0) is 1 for any x (even a zero, quiet NaN, or infinity) > pown(±0, n) is ±∞ and signals the divideByZero exception for odd > integral n<0 > pown(±0, n) is +∞ and signals the divideByZero exception for even > integral n<0 > pown(±0, n) is +0 for even integral n>0 > pown(±0, n) is ±0 for odd integral n>0. > > For the pow function (integral exponents get special treatment): > pow(x, ±0) is 1 for any x (even a zero, quiet NaN, or infinity) > pow(±0, y) is ±∞ and signals the divideByZero exception for y an odd > integer <0 > pow(±0, −∞) is +∞ with no exception > pow(±0, +∞) is +0 with no exception > pow(±0, y) is +∞ and signals the divideByZero exception for finite y<0 > and not an odd integer > pow(±0, y) is ±0 for finite y>0 an odd integer > pow(±0, y) is +0 for finite y>0 and not an odd integer > pow(−1, ±∞) is 1 with no exception > pow(+1, y) is 1 for any y (even a quiet NaN) > pow(x, y) signals the invalid operation exception for finite x<0 and > finite non-integer y" > > So I propose for our text: > > "Raises the first argument to the power of the second argument, > returning the result. The value of power(0,0) is 1. > > Both arguments may be fractional and negative, however, > power(0, y) = NaN for negative y > power(x, y) = NaN for negative x and non integer y. > " > > Steven

Received on Wednesday, 13 December 2017 14:32:53 UTC