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Re: [xsl] Bitwise Operations:More efficient solution?
Subject: Re: [xsl] Bitwise Operations:More efficient solution? From: Chris Maloney <voldrani@xxxxxxxxx> Date: Wed, 16 Feb 2011 10:15:45 -0500 |
[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. > > B <xsl:function name="relpath:bitwiseAnd" as="xs:integer"> > B B <xsl:param name="byte1" as="xs:integer"/> > B B <xsl:param name="byte2" as="xs:integer"/> > > B B <xsl:variable name="byte1Bit7" select="if (($byte1 mod 256) - ($byte1 > mod 128) > 0) then 1 else 0" as="xs:integer"/> > B B <xsl:variable name="byte1Bit6" select="if (($byte1 mod 128) - ($byte1 > mod 64) > 0) then 1 else 0" as="xs:integer"/> > B B <xsl:variable name="byte1Bit5" select="if (($byte1 mod 64) B - ($byte1 > mod 32) > 0) then 1 else 0" as="xs:integer"/> > B B <xsl:variable name="byte1Bit4" select="if (($byte1 mod 32) B - ($byte1 > mod 16) > 0) then 1 else 0" as="xs:integer"/> > B B <xsl:variable name="byte1Bit3" select="if (($byte1 mod 16) B - ($byte1 > mod 8) > 0) then 1 else 0" as="xs:integer"/> > B B <xsl:variable name="byte1Bit2" select="if (($byte1 mod 8) B - ($byte1 > mod 4) > 0) then 1 else 0" as="xs:integer"/> > B B <xsl:variable name="byte1Bit1" select="if (($byte1 mod 4) B - ($byte1 > mod 2) > 0) then 1 else 0" as="xs:integer"/> > B B <xsl:variable name="byte1Bit0" select="if (($byte1 mod 2) B > 0) then 1 > else 0" as="xs:integer"/> > > B B <xsl:variable name="byte2Bit7" select="if (($byte2 mod 256) - ($byte2 > mod 128) > 0) then 1 else 0" as="xs:integer"/> > B B <xsl:variable name="byte2Bit6" select="if (($byte2 mod 128) - ($byte2 > mod 64) > 0) then 1 else 0" as="xs:integer"/> > B B <xsl:variable name="byte2Bit5" select="if (($byte2 mod 64) B - ($byte2 > mod 32) > 0) then 1 else 0" as="xs:integer"/> > B B <xsl:variable name="byte2Bit4" select="if (($byte2 mod 32) B - ($byte2 > mod 16) > 0) then 1 else 0" as="xs:integer"/> > B B <xsl:variable name="byte2Bit3" select="if (($byte2 mod 16) B - ($byte2 > mod 8) > 0) then 1 else 0" as="xs:integer"/> > B B <xsl:variable name="byte2Bit2" select="if (($byte2 mod 8) B - ($byte2 > mod 4) > 0) then 1 else 0" as="xs:integer"/> > B B <xsl:variable name="byte2Bit1" select="if (($byte2 mod 4) B - ($byte2 > mod 2) > 0) then 1 else 0" as="xs:integer"/> > B B <xsl:variable name="byte2Bit0" select="if (($byte2 mod 2) B > 0) then 1 > else 0" as="xs:integer"/> > > B B <xsl:variable name="result" as="xs:integer" > B B B select=" > B B B (128 * $byte2Bit7 * $byte1Bit7) + > B B B (64 * $byte2Bit6 * $byte1Bit6) + > B B B (32 * $byte2Bit5 * $byte1Bit5) + > B B B (16 * $byte2Bit4 * $byte1Bit4) + > B B B (8* $byte2Bit3 * $byte1Bit3) + > B B B (4 * $byte2Bit2 * $byte1Bit2) + > B B B (2 * $byte2Bit1 * $byte1Bit1) + > B B B (1 * $byte2Bit0 * $byte1Bit0) > B B B " > B B /> > B B <xsl:sequence select="$result"/> > B </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
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