Here is an XSLT 2.0 solution using keys. In its current form it
returns the wanted offset (length) as a hexadecimal number. To convert
this to a decimal number, have a look at the archives where AFAIR
there is such code -- could be even posted by me ... This conversion
to decimal can certainly be written elegantly as fold-left() in
XSLT/XPath 3
Also, the key is not generated based on the length of the searched
string (as in Elliot's solution), because I believe the transformation
will be more useful if it can process multiple searches with varying
lengths during the life of the transformation.
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform";>
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:key name="kByteByVal" match="Byte" use="."/>
<xsl:param name="pTarget" select="'04000000FF'"/>
<xsl:template match="/">
<xsl:variable name="vMatchingHeads" select="key('kByteByVal',
substring($pTarget, 1,2))" as="node()*"/>
<xsl:variable name="vSolution" select=
"$vMatchingHeads[string-join(. |
following-sibling::*[not(position() ge string-length($pTarget) idiv
2)], '') eq $pTarget][1]"/>
<xsl:value-of select="$vSolution/@hexAddress"/>
</xsl:template>
</xsl:stylesheet>
When this transformation is applied on the following XML document
(similar to the originally provided one, but added another 04 to make
the case more realistic:
<Bytes>
<Byte hexAddress="0">4D</Byte>
<Byte hexAddress="1">5A</Byte>
<Byte hexAddress="2">90</Byte>
<Byte hexAddress="3">00</Byte>
<Byte hexAddress="4">03</Byte>
<Byte hexAddress="5">04</Byte>
<Byte hexAddress="6">00</Byte>
<Byte hexAddress="7">00</Byte>
<Byte hexAddress="8">00</Byte>
<Byte hexAddress="9">04</Byte>
<Byte hexAddress="A">00</Byte>
<Byte hexAddress="B">00</Byte>
<Byte hexAddress="C">00</Byte>
<Byte hexAddress="D">FF</Byte>
<Byte hexAddress="E">FF</Byte>
</Bytes>
the wanted result is produced:
9
Cheers,
Dimitre
On Tue, Mar 12, 2019 at 11:01 AM Michael Kay mike(_at_)saxonica(_dot_)com
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
My instinct is to use index-of() to get the positions of the elements that
match the first required byte, and then for each of these positions, form the
string of N bytes starting at this position and do a string comparison to
test whether there is a match at this position.
let $candidates := index-of(/Bytes/Byte, substring($req, 1, 2))
return $candidates[string-join(subsequence(/Bytes/Byte, ., $len), '') eq
$req][1] - 1
Michael Kay
Saxoniica
On 12 Mar 2019, at 17:35, Costello, Roger L. costello(_at_)mitre(_dot_)org
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
Hi Folks,
I have an XML document containing a long list of Byte elements, e.g.,
<Bytes>
<Byte hexAddress="0">4D</Byte>
<Byte hexAddress="1">5A</Byte>
<Byte hexAddress="2">90</Byte>
<Byte hexAddress="3">00</Byte>
<Byte hexAddress="4">03</Byte>
<Byte hexAddress="5">00</Byte>
<Byte hexAddress="6">00</Byte>
<Byte hexAddress="7">00</Byte>
<Byte hexAddress="8">04</Byte>
<Byte hexAddress="9">00</Byte>
<Byte hexAddress="A">00</Byte>
<Byte hexAddress="B">00</Byte>
<Byte hexAddress="C">FF</Byte>
<Byte hexAddress="D">FF</Byte>
...
</Bytes>
I have a string of hex values, e.g.,
04000000FF
You can see that the string is contained within this series of Byte
elements:
<Byte hexAddress="8">04</Byte>
<Byte hexAddress="9">00</Byte>
<Byte hexAddress="A">00</Byte>
<Byte hexAddress="B">00</Byte>
<Byte hexAddress="C">FF</Byte>
I want to find the number of <Byte> elements that occur prior to the series
of Byte elements.
I figured one approach is to convert all the Byte text node values into a
string and then perform string manipulations:
string-length(substring-before(string-join(/Bytes/Byte/text(), ''),
'04000000FF')) idiv 2
Note: I divided by two because each Byte has 2 digits.
That seems to work, but I suspect it is horribly inefficient because it
creates a string containing all the Byte text node values and there may be
tens or hundreds of thousands of Byte elements.
What is an efficient way to solve this problem?
/Roger
--
Cheers,
Dimitre Novatchev
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Truly great madness cannot be achieved without significant intelligence.
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To invent, you need a good imagination and a pile of junk
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Never fight an inanimate object
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To avoid situations in which you might make mistakes may be the
biggest mistake of all
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Quality means doing it right when no one is looking.
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You've achieved success in your field when you don't know whether what
you're doing is work or play
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To achieve the impossible dream, try going to sleep.
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write all patents, too? :)
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Sanity is madness put to good use.
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I finally figured out the only reason to be alive is to enjoy it.
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