CODEWITHSUNDEEP
xmlxsltxquery
Saurabh Mullick
Saurabh Mullick

Reputation: 11

How to calculate a power to a variable in xquery?

If I need to calculate a variable "totalIPaddress" whose value is 2^($blocksize) what will be the xquery statement for this?

<IPaddress>
<startIPaddress>192.168.1.1</startIPaddress>
<blocksize>4</blocksize>
</IPaddress>

Upvotes: 1

Views: 1319

Answers (4)

jacknpoe
jacknpoe

Reputation: 1

There is a math:pow function:

math:pow(
    $x as xs:double?,
    $y as xs:numeric
) as xs:double?

Upvotes: 0

Dimitre Novatchev
Dimitre Novatchev

Reputation: 243529

Here is a particularly efficient way of calculating powers -- with logarithmic time complexity (O(log(N)):

declare function local:pow($x as xs:double , $n as xs:integer ) as xs:double
{
  if($n eq 0)
   then 1
   else
    (let $h := $n idiv 2,
         $halfResult := local:pow($x, $h)
      return
            if($n mod 2 eq 0)
              then $halfResult * $halfResult
              else $x * $halfResult * $halfResult
        )

};

local:pow(2,10)

producing the expected correct result:

1024

Upvotes: 2

Michael Kay
Michael Kay

Reputation: 163458

Recursion is your friend:

declare function f:two-to-the($n as xs:integer) as xs:integer {
  if ($n = 0) then 1 else 2 * f:two-to-the($n - 1)
};

Upvotes: 1

BeniBela
BeniBela

Reputation: 16917

Except for math:pow, the simplest way would be to just hardcode it:

(1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536, 131072, 262144, 524288, 1048576, 2097152, 4194304, 8388608, 16777216, 33554432, 67108864, 134217728, 268435456, 536870912, 1073741824, 2147483648, 4294967296)[$blocksize + 1]

works also in XPath 2.

Upvotes: 0

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