Subject: Re: [xsl] Bitwise Operations:More efficient solution? From: Eliot Kimber <ekimber@xxxxxxxxxxxx> Date: Wed, 16 Feb 2011 09:45:09 -0600 |
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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