Re: [basex-talk] Rounding/parsing decimal vs float

Awesome Leo, thanks! Similar to what I was thinking about but with a lot or after-thought optimization! Great suggestion. M.

Il 01 nov 2017 1:59 PM, "Leonard Wörteler" < leonard.woerteler@uni-konstanz.de> ha scritto:

Hi Marco,

I also do not know of a built-in way to do this, but here is my shot at an implementation in XQuery. It uses fast exponentiation [1] and throws a custom error if there is more than one "e" in the input.

Hope that helps (or is of interest), I had fun hacking it together, Leo

declare function local:pow($n, $k) {
  if($k eq 0) then xs:decimal('1')
  else if($k eq 1) then $n
  else (
    let $d := $k idiv 2,
        $m := $k mod 2
    return if($m eq 0) then local:pow($n * $n, $d)
    else local:pow($n * $n, $d) * $n
  )
};

declare function local:parse-decimal($str as xs:string) as xs:decimal {
  let $parts := tokenize($str, '[eE]')
  return switch(count($parts))
    case 1 return xs:decimal($str)
    case 2 return (
      let $exp  := xs:long($parts[2]),
          $base := xs:decimal($parts[1]),
          $b10  := if($exp gt 0) then xs:decimal('10') else

xs:decimal('0.1') return $base * local:pow($b10, $exp) ) default return error(xs:QName('local:NODECIML'), 'Wrong format: ' || $str) };

local:parse-decimal('123.45e-300')

[1] https://en.wikipedia.org/wiki/Exponentiation_by_squaring

Am Mittwoch, 01. November 2017 13:21 CET, Marco Lettere < m.lettere@gmail.com> schrieb:

...

Thanks Kristian, unfortunately this introduces rounding errors which I'm trying to avoid because managing units, measures and monetary amounts. M.

Il 01 nov 2017 12:57 PM, "Kristian Kankainen" kristian@keeleleek.ee ha scritto:

You need to use xs:float or xs:double instead of xs:decimal to be able to use the 'e' or 'E' as the exponent separator.

Br, Kristian K1. nov 2017 13:18 kirjutas kuupäeval Marco Lettere < m.lettere@gmail.com>:

...

Hi all,

I thought of asking this in parallel of hacking my own parsing

procedure

...

...

...

Is there a native way to parse scientific notation string into xs:decimal since a direct casting (xs:decimal("1e1")) is not allowed?

Thanks,

Marco.