Subject: Re: [xsl] Bitwise Operations:More efficient solution? From: Wolfgang Laun <wolfgang.laun@xxxxxxxxx> Date: Wed, 16 Feb 2011 17:03:37 +0100 |
I think its easy to write functions such as this one: <xsl:function name="wl:bitand" as="xsd:integer"> <xsl:param name="a" as="xsd:integer"/> <xsl:param name="b" as="xsd:integer"/> <xsl:param name="n" as="xsd:integer"/> <xsl:choose> <xsl:when test="$n = 0"> <xsl:value-of select="0"/> </xsl:when> <xsl:otherwise> <xsl:variable name="x" as="xsd:integer" select="($a mod 2)*($b mod 2)"/> <xsl:value-of select="2* wl:bitand($a idiv 2, $b idiv 2, $n - 1) + $x"/> </xsl:otherwise> </xsl:choose> </xsl:function> And call it like this <xsl:value-of select="wl:bitand(@a, @b, 8)"/> or wrap this in a function supplying the initial 8. -W On 16 February 2011 16:45, Eliot Kimber <ekimber@xxxxxxxxxxxx> wrote: > > Cool, that helps. > > This is specific to UTF-8 decoding, but I sort of wanted to have generic > bitwise operations. I was actually surprised those aren't in the base > operators but whatever. > > Cheers, > > E. > On 2/16/11 9:15 AM, "Chris Maloney" <voldrani@xxxxxxxxx> wrote: > > > [Sorry, hit the "Send" button by mistake.] > > > > I thought of some more optimizations on the way to work this morning. > > First of all, you can simplify your expressions: > > > > .... > > <xsl:variable name="byte1Bit7" > > select="if ($byte1 > 127) then 1 else 0" > > as="xs:integer"/> > > <xsl:variable name="byte1Bit6" > > select="if ($byte1 mod 128 > 63) then 1 else 0" > > as="xs:integer"/> > > <xsl:variable name="byte1Bit5" > > select="if ($byte1 mod 64 > 31) then 1 else 0" > > as="xs:integer"/> > > <xsl:variable name="byte1Bit4" > > select="if ($byte1 mod 32 > 15) then 1 else 0" > > as="xs:integer"/> > > <xsl:variable name="byte1Bit3" > > select="if ($byte1 mod 16 > 7) then 1 else 0" > > as="xs:integer"/> > > <xsl:variable name="byte1Bit2" > > select="if ($byte1 mod 8 > 3) then 1 else 0" > > as="xs:integer"/> > > <xsl:variable name="byte1Bit1" > > select="if ($byte1 mod 4 > 1) then 1 else 0" > > as="xs:integer"/> > > <xsl:variable name="byte1Bit0" > > select="$byte1 mod 2" > > as="xs:integer"/> > > ... > > > > Then, it occurred to me that if you're doing bitwise-and specifically > > for utf-8 conversion, then you can optimize this quite a bit. The > > ANDing needed by utf-8 conversion is never to a random bit pattern, > > but instead to fixed bit-masks, where the bits are always grouped > > together. So, for example, you could make a specific function to AND > > with 0x3F: > > > > <xsl:function name="relpath:bitwiseAnd3F" as="xs:integer"> > > <xsl:param name="arg" as="xs:integer"/> > > <xsl:variable name='result' > > as='xs:integer' > > select="$arg mod 64"/> > > <xsl:sequence select="$result"/> > > </xsl:function> > > > > and its complement to AND with 0xC0: > > > > <xsl:function name="relpath:bitwiseAndC0" as="xs:integer"> > > <xsl:param name="byte" as="xs:integer"/> > > <xsl:variable name='result' > > as='xs:integer' > > select="($byte - $byte mod 64) / 64"/> > > <xsl:sequence select="$result"/> > > </xsl:function> > > > > Cheers! > > > > > > On Tue, Feb 15, 2011 at 5:41 PM, Eliot Kimber <ekimber@xxxxxxxxxxxx> wrote: > >> I have implemented UTF-8 URI decoding in XSLT 2. It required that I > >> implement left-shift and bitwise AND operations. Left-shift is easy but > >> bitwise AND is a little more involved. My solution is below, but I'm > >> wondering if there's a more elegant and/or efficient way to do this? > >> > >> My approach was based on info from Ken Holman's site that shows how to > >> calculate each bit of the byte. I do that and then sum the result of > >> multiplying the AND of each bit pair times the appropriate power of two. > >> > >> <xsl:function name="relpath:bitwiseAnd" as="xs:integer"> > >> <xsl:param name="byte1" as="xs:integer"/> > >> <xsl:param name="byte2" as="xs:integer"/> > >> > >> <xsl:variable name="byte1Bit7" select="if (($byte1 mod 256) - ($byte1 > >> mod 128) > 0) then 1 else 0" as="xs:integer"/> > >> <xsl:variable name="byte1Bit6" select="if (($byte1 mod 128) - ($byte1 > >> mod 64) > 0) then 1 else 0" as="xs:integer"/> > >> <xsl:variable name="byte1Bit5" select="if (($byte1 mod 64) - ($byte1 > >> mod 32) > 0) then 1 else 0" as="xs:integer"/> > >> <xsl:variable name="byte1Bit4" select="if (($byte1 mod 32) - ($byte1 > >> mod 16) > 0) then 1 else 0" as="xs:integer"/> > >> <xsl:variable name="byte1Bit3" select="if (($byte1 mod 16) - ($byte1 > >> mod 8) > 0) then 1 else 0" as="xs:integer"/> > >> <xsl:variable name="byte1Bit2" select="if (($byte1 mod 8) - ($byte1 > >> mod 4) > 0) then 1 else 0" as="xs:integer"/> > >> <xsl:variable name="byte1Bit1" select="if (($byte1 mod 4) - ($byte1 > >> mod 2) > 0) then 1 else 0" as="xs:integer"/> > >> <xsl:variable name="byte1Bit0" select="if (($byte1 mod 2) > 0) then 1 > >> else 0" as="xs:integer"/> > >> > >> <xsl:variable name="byte2Bit7" select="if (($byte2 mod 256) - ($byte2 > >> mod 128) > 0) then 1 else 0" as="xs:integer"/> > >> <xsl:variable name="byte2Bit6" select="if (($byte2 mod 128) - ($byte2 > >> mod 64) > 0) then 1 else 0" as="xs:integer"/> > >> <xsl:variable name="byte2Bit5" select="if (($byte2 mod 64) - ($byte2 > >> mod 32) > 0) then 1 else 0" as="xs:integer"/> > >> <xsl:variable name="byte2Bit4" select="if (($byte2 mod 32) - ($byte2 > >> mod 16) > 0) then 1 else 0" as="xs:integer"/> > >> <xsl:variable name="byte2Bit3" select="if (($byte2 mod 16) - ($byte2 > >> mod 8) > 0) then 1 else 0" as="xs:integer"/> > >> <xsl:variable name="byte2Bit2" select="if (($byte2 mod 8) - ($byte2 > >> mod 4) > 0) then 1 else 0" as="xs:integer"/> > >> <xsl:variable name="byte2Bit1" select="if (($byte2 mod 4) - ($byte2 > >> mod 2) > 0) then 1 else 0" as="xs:integer"/> > >> <xsl:variable name="byte2Bit0" select="if (($byte2 mod 2) > 0) then 1 > >> else 0" as="xs:integer"/> > >> > >> <xsl:variable name="result" as="xs:integer" > >> select=" > >> (128 * $byte2Bit7 * $byte1Bit7) + > >> (64 * $byte2Bit6 * $byte1Bit6) + > >> (32 * $byte2Bit5 * $byte1Bit5) + > >> (16 * $byte2Bit4 * $byte1Bit4) + > >> (8* $byte2Bit3 * $byte1Bit3) + > >> (4 * $byte2Bit2 * $byte1Bit2) + > >> (2 * $byte2Bit1 * $byte1Bit1) + > >> (1 * $byte2Bit0 * $byte1Bit0) > >> " > >> /> > >> <xsl:sequence select="$result"/> > >> </xsl:function> > >> > >> Cheers, > >> > >> E. > >> -- > >> Eliot Kimber > >> Senior Solutions Architect > >> "Bringing Strategy, Content, and Technology Together" > >> Main: 512.554.9368 > >> www.reallysi.com > >> www.rsuitecms.com > > > > -- > Eliot Kimber > Senior Solutions Architect > "Bringing Strategy, Content, and Technology Together" > Main: 512.554.9368 > www.reallysi.com > www.rsuitecms.com
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