223 lines
7.6 KiB
Plaintext
223 lines
7.6 KiB
Plaintext
<chapter id="porting">
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<title>Porting Wine to new Platforms</title>
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<para>Porting Wine to different (UNIX-based) operating systems...</para>
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<sect1 id="wine-porting">
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<title>Porting</title>
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<para>
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This document provides a few tips on porting Wine to your
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favorite operating system.
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</para>
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<sect2>
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<title>Why <symbol>#ifdef MyOS</symbol> is probably a mistake.</title>
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<para>
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Operating systems change. Maybe yours doesn't have the
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<filename>foo.h</filename> header, but maybe a future
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version will have it. If you want to <symbol>#include
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<foo.h></symbol>, it doesn't matter what operating
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system you are using; it only matters whether
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<filename>foo.h</filename> is there.
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</para>
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<para>
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Furthermore, operating systems change names or "fork" into
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several ones. An <symbol>#ifdef MyOs</symbol> will break
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over time.
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</para>
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<para>
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If you use the feature of <command>autoconf</command> -- the
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Gnu auto-configuration utility -- wisely, you will help
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future porters automatically because your changes will test
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for <emphasis>features</emphasis>, not names of operating
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systems. A feature can be many things:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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existence of a header file
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</para>
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</listitem>
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<listitem>
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<para>
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existence of a library function
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</para>
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</listitem>
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<listitem>
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<para>
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existence of libraries
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</para>
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</listitem>
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<listitem>
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<para>
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bugs in header files, library functions, the compiler, ...
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</para>
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</listitem>
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</itemizedlist>
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<para>
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You will need Gnu Autoconf, which you can get from your
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friendly Gnu mirror. This program takes Wine's
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<filename>configure.ac</filename> file and produces a
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<filename>configure</filename> shell script that users use
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to configure Wine to their system.
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</para>
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<para>
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There <emphasis>are</emphasis> exceptions to the "avoid
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<symbol>#ifdef MyOS</symbol>" rule. Wine, for example, needs
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the internals of the signal stack -- that cannot easily be
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described in terms of features. Moreover, you can not use
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<filename>autoconf</filename>'s <symbol>HAVE_*</symbol>
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symbols in Wine's headers, as these may be used by Winelib
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users who may not be using a <filename>configure</filename>
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script.
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</para>
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<para>
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Let's now turn to specific porting problems and how to solve
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them.
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</para>
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</sect2>
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<sect2>
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<title>MyOS doesn't have the <filename>foo.h</filename> header!</title>
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<para>
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This first step is to make <command>autoconf</command> check
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for this header. In <filename>configure.in</filename> you
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add a segment like this in the section that checks for
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header files (search for "header files"):
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</para>
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<programlisting>
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AC_CHECK_HEADER(foo.h, AC_DEFINE(HAVE_FOO_H))
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</programlisting>
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<para>
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If your operating system supports a header file with the
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same contents but a different name, say
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<filename>bar.h</filename>, add a check for that also.
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</para>
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<para>
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Now you can change
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</para>
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<programlisting>
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#include <foo.h>
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</programlisting>
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<para>
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to
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</para>
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<programlisting>
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#ifdef HAVE_FOO_H
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#include <foo.h>
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#elif defined (HAVE_BAR_H)
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#include <bar.h>
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#endif
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</programlisting>
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<para>
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If your system doesn't have a corresponding header file even
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though it has the library functions being used, you might
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have to add an <symbol>#else</symbol> section to the
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conditional. Avoid this if you can.
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</para>
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<para>
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You will also need to add <symbol>#undef HAVE_FOO_H</symbol>
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(etc.) to <filename>include/config.h.in</filename>
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</para>
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<para>
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Finish up with <command>make configure</command> and
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<command>./configure</command>.
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</para>
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</sect2>
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<sect2>
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<title>MyOS doesn't have the <function>bar</function> function!</title>
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<para>
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A typical example of this is the
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<function>memmove</function> function. To solve this
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problem you would add <function>memmove</function> to the
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list of functions that <command>autoconf</command> checks
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for. In <filename>configure.in</filename> you search for
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<function>AC_CHECK_FUNCS</function> and add
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<function>memmove</function>. (You will notice that someone
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already did this for this particular function.)
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</para>
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<para>
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Secondly, you will also need to add <symbol>#undef
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HAVE_BAR</symbol> to
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<filename>include/config.h.in</filename>
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</para>
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<para>
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The next step depends on the nature of the missing function.
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</para>
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<variablelist>
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<varlistentry>
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<term>Case 1:</term>
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<listitem>
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<para>
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It's easy to write a complete implementation of the
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function. (<function>memmove</function> belongs to
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this case.)
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</para>
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<para>
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You add your implementation in
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<filename>misc/port.c</filename> surrounded by
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<symbol>#ifndef HAVE_MEMMOVE</symbol> and
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<symbol>#endif</symbol>.
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</para>
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<para>
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You might have to add a prototype for your function.
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If so, <filename>include/miscemu.h</filename> might be the place. Don't
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forget to protect that definition by <symbol>#ifndef
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HAVE_MEMMOVE</symbol> and <symbol>#endif</symbol> also!
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Case 2:</term>
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<listitem>
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<para>
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A general implementation is hard, but Wine is only
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using a special case.
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</para>
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<para>
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An example is the various <function>wait</function>
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calls used in <function>SIGNAL_child</function> from
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<filename>loader/signal.c</filename>. Here we have a
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multi-branch case on features:
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</para>
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<programlisting>
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#ifdef HAVE_THIS
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...
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#elif defined (HAVE_THAT)
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...
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#elif defined (HAVE_SOMETHING_ELSE)
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...
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#endif
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</programlisting>
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<para>
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Note that this is very different from testing on
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operating systems. If a new version of your operating
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systems comes out and adds a new function, this code
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will magically start using it.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>
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Finish up with <command>make configure</command> and
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<command>./configure</command>.
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</para>
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</sect2>
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</sect1>
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</chapter>
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