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<para>FreeBSD traces its roots back nearly twenty years to the <para>FreeBSD traces its roots back nearly twenty years to the
work of the Computer Science Research Group at the work of the Computer Science Research Group at the
University of California Berkeley.<footnote> University of California Berkeley.<footnote>
<simpara>FreeBSD's <link xlink:href="http://cvsweb.freebsd.org/">source <simpara>FreeBSD's <link xlink:href="http://svnweb.freebsd.org/">source
repository</link> contains a history of the project repository</link> contains a history of the project
since its inception, and there are <link xlink:href="http://www.mckusick.com/csrg/">CDROMs since its inception, and there are <link xlink:href="http://www.mckusick.com/csrg/">CDROMs
available</link> that contain earlier code from the available</link> that contain earlier code from the
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<figure xml:id="fig-change-log"> <figure xml:id="fig-change-log">
<title>A sample change log entry</title> <title>A sample change log entry</title>
<programlisting> <programlisting>
bde 2005-10-29 16:34:50 UTC r151864 | bde | 2005-10-29 09:34:50 -0700 (Sat, 29 Oct 2005) | 13 lines
Changed paths:
M /head/lib/msun/src/e_rem_pio2f.c
FreeBSD src repository Use double precision to simplify and optimize arg reduction for small
and medium size args too: instead of conditionally subtracting a float
17+24, 17+17+24 or 17+17+17+24 bit approximation to pi/2, always
subtract a double 33+53 bit one. The float version is now closer to
the double version than to old versions of itself -- it uses the same
33+53 bit approximation as the simplest cases in the double version,
and where the float version had to switch to the slow general case at
|x| == 2^7*pi/2, it now switches at |x| == 2^19*pi/2 the same as the
double version.
Modified files: This speeds up arg reduction by a factor of 2 for |x| between 3*pi/4 and
lib/msun/src e_rem_pio2f.c 2^7*pi/4, and by a factor of 7 for |x| between 2^7*pi/4 and 2^19*pi/4.
Log:
Use double precision to simplify and optimize arg reduction for small
and medium size args too: instead of conditionally subtracting a float
17+24, 17+17+24 or 17+17+17+24 bit approximation to pi/2, always
subtract a double 33+53 bit one. The float version is now closer to
the double version than to old versions of itself &mdash; it uses the same
33+53 bit approximation as the simplest cases in the double version,
and where the float version had to switch to the slow general case at
|x| == 2^7*pi/2, it now switches at |x| == 2^19*pi/2 the same as the
double version.
This speeds up arg reduction by a factor of 2 for |x| between 3*pi/4 and
2^7*pi/4, and by a factor of 7 for |x| between 2^7*pi/4 and 2^19*pi/4.
Revision Changes Path
1.14 +22 -97 src/lib/msun/src/e_rem_pio2f.c
</programlisting> </programlisting>
</figure> </figure>
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FreeBSD. For example:</para> FreeBSD. For example:</para>
<formalpara> <formalpara>
<title>Track FreeBSD source code</title> <title>Track FreeBSD source code</title>
<para>The project makes it easy to mirror its CVS <para>The project makes it easy to mirror its SVN
repository using <link xlink:href="&url.articles.cvsup-advanced;"><!-- repository using <link xlink:href="&url.articles.committers-guide;/subversion-primer.html#svn-advanced-use-setting-up-svnsync"><!--
--><application>CVSup</application></link>. Having --><application>svnsync</application></link>. Having
the complete history of the source is useful when the complete history of the source is useful when
debugging complex problems and offers valuable insight debugging complex problems and offers valuable insight
into the intentions of the original developers. Use a into the intentions of the original developers. Use a
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easily merge changes between the upstream FreeBSD code easily merge changes between the upstream FreeBSD code
base and your own in-house code.</para> base and your own in-house code.</para>
</formalpara> </formalpara>
<para><xref linkend="fig-cvs-annotate"/> shows a portion of <para><xref linkend="fig-svn-blame"/> shows a portion of
an annotated listing of the file referenced by the an annotated listing of the file referenced by the
change log in <xref linkend="fig-change-log"/>. The change log in <xref linkend="fig-change-log"/>. The
ancestry of each line of the source is clearly visible. ancestry of each line of the source is clearly visible.
Annotated listings showing the history of every file Annotated listings showing the history of every file
that is part of FreeBSD are <link xlink:href="http://cvsweb.freebsd.org/">available on the that is part of FreeBSD are <link xlink:href="http://svnweb.freebsd.org/">available on the
web</link>.</para> web</link>.</para>
<figure xml:id="fig-cvs-annotate"> <figure xml:id="fig-svn-blame">
<title>An annotated source listing generated using <command>cvs annotate</command></title> <title>An annotated source listing generated using <command>svn blame</command></title>
<programlisting> <programlisting>
<![CDATA[ <![CDATA[
#LINE #REV #WHO #DATE #TEXT #REV #WHO #DATE #TEXT
62 1.1 (jkh 19-Aug-94): int32_t __ieee754_rem_pio2f(float x, float *y) 176410 bde 2008-02-19 07:42:46 -0800 (Tue, 19 Feb 2008) #include <sys/cdefs.h>
63 1.1 (jkh 19-Aug-94): { 176410 bde 2008-02-19 07:42:46 -0800 (Tue, 19 Feb 2008) __FBSDID("$FreeBSD$");
64 1.14 (bde 29-Oct-05): double z,w,t,r,fn; 2116 jkh 1994-08-19 02:40:01 -0700 (Fri, 19 Aug 1994)
65 1.13 (bde 29-Oct-05): double tx[3]; 2116 jkh 1994-08-19 02:40:01 -0700 (Fri, 19 Aug 1994) /* __ieee754_rem_pio2f(x,y)
66 1.14 (bde 29-Oct-05): int32_t e0,i,nx,n,ix,hx; 8870 rgrimes 1995-05-29 22:51:47 -0700 (Mon, 29 May 1995) *
67 1.1 (jkh 19-Aug-94): 176552 bde 2008-02-25 05:33:20 -0800 (Mon, 25 Feb 2008) * return the remainder of x rem pi/2 in *y
68 1.1 (jkh 19-Aug-94): GET_FLOAT_WORD(hx,x); 176552 bde 2008-02-25 05:33:20 -0800 (Mon, 25 Feb 2008) * use double precision for everything except passing x
69 1.1 (jkh 19-Aug-94): ix = hx&0x7fffffff; 152535 bde 2005-11-16 18:20:04 -0800 (Wed, 16 Nov 2005) * use __kernel_rem_pio2() for large x
70 1.1 (jkh 19-Aug-94): if(ix<=0x3f490fd8) /* |x| ~<= pi/4 , no need for reduction */ 2116 jkh 1994-08-19 02:40:01 -0700 (Fri, 19 Aug 1994) */
71 1.1 (jkh 19-Aug-94): {y[0] = x; y[1] = 0; return 0;} 2116 jkh 1994-08-19 02:40:01 -0700 (Fri, 19 Aug 1994)
72 1.14 (bde 29-Oct-05): /* 33+53 bit pi is good enough for special and medium size cases */ 176465 bde 2008-02-22 07:55:14 -0800 (Fri, 22 Feb 2008) #include <float.h>
73 1.2 (bde 07-Apr-95): if(ix<0x4016cbe4) { /* |x| < 3pi/4, special case with n=+-1 */ 176465 bde 2008-02-22 07:55:14 -0800 (Fri, 22 Feb 2008)
74 1.14 (bde 29-Oct-05): if(hx>0) { 2116 jkh 1994-08-19 02:40:01 -0700 (Fri, 19 Aug 1994) #include "math.h"
75 1.15 (bde 06-Nov-05): z = x - pio2;
76 1.15 (bde 06-Nov-05): n = 1;
77 1.15 (bde 06-Nov-05): } else {
78 1.15 (bde 06-Nov-05): z = x + pio2;
79 1.15 (bde 06-Nov-05): n = 3;
80 1.9 (bde 08-Oct-05): }
81 1.15 (bde 06-Nov-05): y[0] = z;
82 1.15 (bde 06-Nov-05): y[1] = z - y[0];
83 1.15 (bde 06-Nov-05): return n;
84 1.15 (bde 06-Nov-05): }
85 1.15 (bde 06-Nov-05): if(ix<0x407b53d1) { /* |x| < 5*pi/4, special case with n=+-2 */
]]> ]]>
</programlisting> </programlisting>
</figure> </figure>
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