Re: [xsl] How to convert a recursive function to a loop, using XSLT 2.0?

["Dimitre Novatchev dnovatchev@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Hi Roger,

Besides the obvious grouping solution, here is a short XPath 2.0 (plus some
XSLT 2.0) to do this in a non-recursive way.

Ideally I would use no XSLT and pure XPath 3 -- taking advantage of XPath
3.0 features such as the let - expression and maps, and also the ability to
generate XML as a string and then use the standard parse-xml() function to
construct a new XML document, using only XPath.

One can also produce an XSLT 1.0 solution, using keys.

This XSLT 2.0 transformation:

<xsl:stylesheet version="2.0" xmlns:xsl="
http://www.w3.org/1999/XSL/Transform";
 xmlns:xs="http://www.w3.org/2001/XMLSchema"; xmlns:my="my:my"
 exclude-result-prefixes="xs my">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>

  <xsl:variable name="vHex2Dec">
    <tr from="48" to="72"/>
    <tr from="4A" to="74"/>
    <tr from="69" to="105"/>
    <tr from="6C" to="108"/>
  </xsl:variable>

  <xsl:template match="/">
    <xsl:variable name="vBytes" select="/*/Byte"/>
    <xsl:variable name="vEnds" select="index-of($vBytes, '00')"/>

    <xsl:sequence select=
    "for $vLastEnd in (0, $vEnds),
         $vThisEnd in $vEnds[. > $vLastEnd][1]
       return
          my:makeString(
            for $pos in $vLastEnd+1 to $vThisEnd -1
      return
        $vHex2Dec/*[@from = $vBytes[$pos]]/@to/xs:integer(.)
                        )

    "/>
  </xsl:template>

  <xsl:function name="my:makeString" as="element()">
    <xsl:param name="pCodepoints" as="xs:integer*"/>

    <string>
      <xsl:sequence select="codepoints-to-string($pCodepoints)"/>
    </string>
  </xsl:function>
</xsl:stylesheet>

When applied on the provided XML fragment (made a wellformed XML document):

<t>
<Byte>48</Byte>
<Byte>69</Byte>
<Byte>00</Byte>
<Byte>4A</Byte>
<Byte>69</Byte>
<Byte>6C</Byte>
<Byte>6C</Byte>
<Byte>00</Byte>
</t>

produces the wanted result:

<string>Hi</string>
<string>Jill</string>


Cheers,
Dimitre


On Fri, May 10, 2019 at 4:20 AM Costello, Roger L. costello@xxxxxxxxx <
xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:

> Hello XSLT experts!
>
> My input file consists of a sequence (sourceSeq) of <Byte> elements
> representing a sequence of null-terminated strings. I want to create a
> function that returns a sequence of <String> elements. For example, with
> this sourceSeq:
>
> <Byte>48</Byte>
> <Byte>69</Byte>
> <Byte>00</Byte>
> <Byte>4A</Byte>
> <Byte>69</Byte>
> <Byte>6C</Byte>
> <Byte>6C</Byte>
> <Byte>00</Byte>
>
> the function should return:
>
> <String>Hi</String>
> <String>Jill</String>
>
> The strings are of variable length.
>
> I do not know how many null-terminated strings are in sourceSeq. However,
> I do know the total number (total-size) of <Byte> elements within sourceSeq
> containing the null-terminated strings.
>
> Below is a recursive way to implement the function. Unfortunately,
> total-size can be quite large, which means the function recurses many
> times, resulting in a "Too many nested function calls" error. Is there an
> iterative way to implement the function?  /Roger
>
> <xsl:function name="f:make-string-table-entries" as="element(String)*">
>     <xsl:param name="total-size" as="xs:integer" />
>     <xsl:param name="current-size" as="xs:integer" />
>     <xsl:param name="current-position" as="xs:integer" />
>     <xsl:param name="sourceSeq" as="element(Byte)*" />
>
>     <xsl:choose>
>         <xsl:when test="$current-size ge $total-size" />
>         <xsl:otherwise>
>             <xsl:variable name="string"
> select="f:make-element-from-null-terminated-string('String',
> $current-position, $sourceSeq)" as="element(String)"/>
>             <xsl:sequence select="$string" />
>             <xsl:variable name="length"
> select="string-length($string/text()) + 1"/>  <!-- add 1 for the null byte
> -->
>             <xsl:sequence select="f:make-string-table-entries($total-size,
> xs:integer($current-size+$length), xs:integer($current-position+$length),
> $sourceSeq)" />
>         </xsl:otherwise>
>     </xsl:choose>
>
> </xsl:function>
> 
>


-- 
Cheers,
Dimitre Novatchev
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