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<h1 class="settitle">Porting libstdc++-v3</h1>
<div class="node">
<p><hr>
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<h2 class="unnumbered">Porting libstdc++-v3</h2>

<p>This document explains how to port libstdc++-v3 (the GNU C++ library) to
a new target.

   <p>In order to make the GNU C++ library (libstdc++-v3) work with a new
target, you must edit some configuration files and provide some new
header files.  Unless this is done, libstdc++-v3 will use generic
settings which may not be correct for your target; even if they are
correct, they will likely be inefficient.

   <p>Before you get started, make sure that you have a working C library on
your target.  The C library need not precisely comply with any
particular standard, but should generally conform to the requirements
imposed by the ANSI/ISO standard.

   <p>In addition, you should try to verify that the C++ compiler generally
works.  It is difficult to test the C++ compiler without a working
library, but you should at least try some minimal test cases.

   <p>(Note that what we think of as a "target," the library refers to as
a "host."  The comment at the top of <code>configure.ac</code> explains why.)

   <p>Here are the primary steps required to port the library:

<ul class="menu">
<li><a accesskey="1" href="#Operating%20system">Operating system</a>:     Configuring for your operating system. 
<li><a accesskey="2" href="#CPU">CPU</a>:                  Configuring for your processor chip. 
<li><a accesskey="3" href="#Character%20types">Character types</a>:      Implementing character classification. 
<li><a accesskey="4" href="#Thread%20safety">Thread safety</a>:        Implementing atomic operations. 
<li><a accesskey="5" href="#Numeric%20limits">Numeric limits</a>: 	Implementing numeric limits. 
<li><a accesskey="6" href="#Libtool">Libtool</a>:              Using libtool. 
<li><a accesskey="7" href="#GNU%20Free%20Documentation%20License">GNU Free Documentation License</a>:  How you can copy and share this manual. 
</ul>

<div class="node">
<p><hr>
Node:&nbsp;<a name="Operating%20system">Operating system</a>,
Next:&nbsp;<a rel="next" accesskey="n" href="#CPU">CPU</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#Top">Top</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#Top">Top</a>
<br>
</div>

<h2 class="chapter">Operating system</h2>

<p>If you are porting to a new operating system (as opposed to a new chip
using an existing operating system), you will need to create a new
directory in the <code>config/os</code> hierarchy.  For example, the IRIX
configuration files are all in <code>config/os/irix</code>.  There is no set
way to organize the OS configuration directory.  For example,
<code>config/os/solaris/solaris-2.6</code> and
<code>config/os/solaris/solaris-2.7</code> are used as configuration
directories for these two versions of Solaris.  On the other hand, both
Solaris 2.7 and Solaris 2.8 use the <code>config/os/solaris/solaris-2.7</code>
directory.  The important information is that there needs to be a
directory under <code>config/os</code> to store the files for your operating
system.

   <p>You might have to change the <code>configure.host</code> file to ensure that
your new directory is activated.  Look for the switch statement that sets
<code>os_include_dir</code>, and add a pattern to handle your operating system
if the default will not suffice.  The switch statement switches on only
the OS portion of the standard target triplet; e.g., the <code>solaris2.8</code>
in <code>sparc-sun-solaris2.8</code>.  If the new directory is named after the
OS portion of the triplet (the default), then nothing needs to be changed.

   <p>The first file to create in this directory, should be called
<code>os_defines.h</code>.  This file contains basic macro definitions
that are required to allow the C++ library to work with your C library. 
This file should provide macro definitions for <code>__off_t</code>,
<code>__off64_t</code>, and <code>__ssize_t</code>.  Typically, this just looks
like:

<pre class="example">     #define __off_t off_t
     #define __off64_t off64_t
     #define __ssize_t ssize_t
     </pre>

<p>You don't have to provide these definitions if your system library
already defines these types - but the only library known to provide
these types is the GNU C Library, so you will almost certainly have to
provide these macros.  Note that this file does not have to include a
header file that defines <code>off_t</code>, or the other types; you simply
have to provide the macros.

   <p>In addition, several libstdc++-v3 source files unconditionally define
the macro <code>_POSIX_SOURCE</code>.  On many systems, defining this macro
causes large portions of the C library header files to be eliminated
at preprocessing time.  Therefore, you may have to <code>#undef</code> this
macro, or define other macros (like <code>_LARGEFILE_SOURCE</code> or
<code>__EXTENSIONS__</code>).  You won't know what macros to define or
undefine at this point; you'll have to try compiling the library and
seeing what goes wrong.  If you see errors about calling functions
that have not been declared, look in your C library headers to see if
the functions are declared there, and then figure out what macros you
need to define.  You will need to add them to the
<code>CPLUSPLUS_CPP_SPEC</code> macro in the GCC configuration file for your
target.  It will not work to simply define these macros in
<code>os_defines.h</code>.

   <p>At this time, there are a few libstdc++-v3-specific macros which may be
defined:

   <p><code>_GLIBCXX_USE_C99_CHECK</code> may be defined to 1 to check C99
function declarations (which are not covered by specialization below)
found in system headers against versions found in the library headers
derived from the standard.

   <p><code>_GLIBCXX_USE_C99_DYNAMIC</code> may be defined to an expression that
yields 0 if and only if the system headers are exposing proper support
for C99 functions (which are not covered by specialization below).  If
defined, it must be 0 while bootstrapping the compiler/rebuilding the
library.

   <p><code>_GLIBCXX_USE_C99_LONG_LONG_CHECK</code> may be defined to 1 to check
the set of C99 long long function declarations found in system headers
against versions found in the library headers derived from the
standard.

   <p><code>_GLIBCXX_USE_C99_LONG_LONG_DYNAMIC</code> may be defined to an
expression that yields 0 if and only if the system headers are
exposing proper support for the set of C99 long long functions.  If
defined, it must be 0 while bootstrapping the compiler/rebuilding the
library.

   <p><code>_GLIBCXX_USE_C99_FP_MACROS_DYNAMIC</code> may be defined to an
expression that yields 0 if and only if the system headers
are exposing proper support for the related set of macros.  If defined,
it must be 0 while bootstrapping the compiler/rebuilding the library.

   <p><code>_GLIBCXX_USE_C99_FLOAT_TRANSCENDENTALS_CHECK</code> may be defined
to 1 to check the related set of function declarations found in system
headers against versions found in the library headers derived from
the standard.

   <p><code>_GLIBCXX_USE_C99_FLOAT_TRANSCENDENTALS_DYNAMIC</code> may be defined
to an expression that yields 0 if and only if the system headers
are exposing proper support for the related set of functions.  If defined,
it must be 0 while bootstrapping the compiler/rebuilding the library.

   <p>Finally, you should bracket the entire file in an include-guard, like
this:

<pre class="example">     #ifndef _GLIBCXX_OS_DEFINES
     #define _GLIBCXX_OS_DEFINES
     ...
     #endif
     </pre>

   <p>We recommend copying an existing <code>os_defines.h</code> to use as a
starting point.

<div class="node">
<p><hr>
Node:&nbsp;<a name="CPU">CPU</a>,
Next:&nbsp;<a rel="next" accesskey="n" href="#Character%20types">Character types</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#Operating%20system">Operating system</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#Top">Top</a>
<br>
</div>

<h2 class="chapter">CPU</h2>

<p>If you are porting to a new chip (as opposed to a new operating system
running on an existing chip), you will need to create a new directory in the
<code>config/cpu</code> hierarchy.  Much like the <a href="#Operating%20system">Operating system</a> setup,
there are no strict rules on how to organize the CPU configuration
directory, but careful naming choices will allow the configury to find your
setup files without explicit help.

   <p>We recommend that for a target triplet <code>&lt;CPU&gt;-&lt;vendor&gt;-&lt;OS&gt;</code>, you
name your configuration directory <code>config/cpu/&lt;CPU&gt;</code>.  If you do this,
the configury will find the directory by itself.  Otherwise you will need to
edit the <code>configure.host</code> file and, in the switch statement that sets
<code>cpu_include_dir</code>, add a pattern to handle your chip.

   <p>Note that some chip families share a single configuration directory, for
example, <code>alpha</code>, <code>alphaev5</code>, and <code>alphaev6</code> all use the
<code>config/cpu/alpha</code> directory, and there is an entry in the
<code>configure.host</code> switch statement to handle this.

   <p>The <code>cpu_include_dir</code> sets default locations for the files controlling
<a href="#Thread%20safety">Thread safety</a> and <a href="#Numeric%20limits">Numeric limits</a>, if the defaults are not
appropriate for your chip.

<div class="node">
<p><hr>
Node:&nbsp;<a name="Character%20types">Character types</a>,
Next:&nbsp;<a rel="next" accesskey="n" href="#Thread%20safety">Thread safety</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#CPU">CPU</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#Top">Top</a>
<br>
</div>

<h2 class="chapter">Character types</h2>

<p>The library requires that you provide three header files to implement
character classification, analogous to that provided by the C libraries
<code>&lt;ctype.h&gt;</code> header.  You can model these on the files provided in
<code>config/os/generic</code>.  However, these files will almost
certainly need some modification.

   <p>The first file to write is <code>ctype_base.h</code>.  This file provides
some very basic information about character classification.  The libstdc++-v3
library assumes that your C library implements <code>&lt;ctype.h&gt;</code> by using
a table (indexed by character code) containing integers, where each of
these integers is a bit-mask indicating whether the character is
upper-case, lower-case, alphabetic, etc.  The <code>ctype_base.h</code>
file gives the type of the integer, and the values of the various bit
masks.  You will have to peer at your own <code>&lt;ctype.h&gt;</code> to figure out
how to define the values required by this file.

   <p>The <code>ctype_base.h</code> header file does not need include guards. 
It should contain a single <code>struct</code> definition called
<code>ctype_base</code>.  This <code>struct</code> should contain two type
declarations, and one enumeration declaration, like this example, taken
from the IRIX configuration:

<pre class="example">     struct ctype_base
     {
       typedef unsigned int 	mask;
       typedef int* 		__to_type;
     
       enum
       {
         space = _ISspace,
         print = _ISprint,
         cntrl = _IScntrl,
         upper = _ISupper,
         lower = _ISlower,
         alpha = _ISalpha,
         digit = _ISdigit,
         punct = _ISpunct,
         xdigit = _ISxdigit,
         alnum = _ISalnum,
         graph = _ISgraph
       };
     };
     </pre>

<p>The <code>mask</code> type is the type of the elements in the table.  If your
C library uses a table to map lower-case numbers to upper-case numbers,
and vice versa, you should define <code>__to_type</code> to be the type of the
elements in that table.  If you don't mind taking a minor performance
penalty, or if your library doesn't implement <code>toupper</code> and
<code>tolower</code> in this way, you can pick any pointer-to-integer type,
but you must still define the type.

   <p>The enumeration should give definitions for all the values in the above
example, using the values from your native <code>&lt;ctype.h&gt;</code>.  They can
be given symbolically (as above), or numerically, if you prefer.  You do
not have to include <code>&lt;ctype.h&gt;</code> in this header; it will always be
included before <code>ctype_base.h</code> is included.

   <p>The next file to write is <code>ctype_noninline.h</code>, which also does
not require include guards.  This file defines a few member functions
that will be included in <code>include/bits/locale_facets.h</code>.  The first
function that must be written is the <code>ctype&lt;char&gt;::ctype</code>
constructor.  Here is the IRIX example:

<pre class="example">     ctype&lt;char&gt;::ctype(const mask* __table = 0, bool __del = false,
           size_t __refs = 0)
       : _Ctype_nois&lt;char&gt;(__refs), _M_del(__table != 0 &amp;&amp; __del),
         _M_toupper(NULL),
         _M_tolower(NULL),
         _M_ctable(NULL),
         _M_table(!__table
                  ? (const mask*) (__libc_attr._ctype_tbl-&gt;_class + 1)
                  : __table)
       { }
     </pre>

<p>There are two parts of this that you might choose to alter. The first,
and most important, is the line involving <code>__libc_attr</code>.  That is
IRIX system-dependent code that gets the base of the table mapping
character codes to attributes.  You need to substitute code that obtains
the address of this table on your system.  If you want to use your
operating system's tables to map upper-case letters to lower-case, and
vice versa, you should initialize <code>_M_toupper</code> and
<code>_M_tolower</code> with those tables, in similar fashion.

   <p>Now, you have to write two functions to convert from upper-case to
lower-case, and vice versa.  Here are the IRIX versions:

<pre class="example">     char
     ctype&lt;char&gt;::do_toupper(char __c) const
     { return _toupper(__c); }
     
     char
     ctype&lt;char&gt;::do_tolower(char __c) const
     { return _tolower(__c); }
     </pre>

<p>Your C library provides equivalents to IRIX's <code>_toupper</code> and
<code>_tolower</code>.  If you initialized <code>_M_toupper</code> and
<code>_M_tolower</code> above, then you could use those tables instead.

   <p>Finally, you have to provide two utility functions that convert strings
of characters.  The versions provided here will always work - but you
could use specialized routines for greater performance if you have
machinery to do that on your system:

<pre class="example">     const char*
     ctype&lt;char&gt;::do_toupper(char* __low, const char* __high) const
     {
       while (__low &lt; __high)
         {
           *__low = do_toupper(*__low);
           ++__low;
         }
       return __high;
     }
     
     const char*
     ctype&lt;char&gt;::do_tolower(char* __low, const char* __high) const
     {
       while (__low &lt; __high)
         {
           *__low = do_tolower(*__low);
           ++__low;
         }
       return __high;
     }
     </pre>

   <p>You must also provide the <code>ctype_inline.h</code> file, which
contains a few more functions.  On most systems, you can just copy
<code>config/os/generic/ctype_inline.h</code> and use it on your system.

   <p>In detail, the functions provided test characters for particular
properties; they are analogous to the functions like <code>isalpha</code> and
<code>islower</code> provided by the C library.

   <p>The first function is implemented like this on IRIX:

<pre class="example">     bool
     ctype&lt;char&gt;::
     is(mask __m, char __c) const throw()
     { return (_M_table)[(unsigned char)(__c)] &amp; __m; }
     </pre>

<p>The <code>_M_table</code> is the table passed in above, in the constructor. 
This is the table that contains the bitmasks for each character.  The
implementation here should work on all systems.

   <p>The next function is:

<pre class="example">     const char*
     ctype&lt;char&gt;::
     is(const char* __low, const char* __high, mask* __vec) const throw()
     {
       while (__low &lt; __high)
         *__vec++ = (_M_table)[(unsigned char)(*__low++)];
       return __high;
     }
     </pre>

<p>This function is similar; it copies the masks for all the characters
from <code>__low</code> up until <code>__high</code> into the vector given by
<code>__vec</code>.

   <p>The last two functions again are entirely generic:

<pre class="example">     const char*
     ctype&lt;char&gt;::
     scan_is(mask __m, const char* __low, const char* __high) const throw()
     {
       while (__low &lt; __high &amp;&amp; !this-&gt;is(__m, *__low))
         ++__low;
       return __low;
     }
     
     const char*
     ctype&lt;char&gt;::
     scan_not(mask __m, const char* __low, const char* __high) const throw()
     {
       while (__low &lt; __high &amp;&amp; this-&gt;is(__m, *__low))
         ++__low;
       return __low;
     }
     </pre>

<div class="node">
<p><hr>
Node:&nbsp;<a name="Thread%20safety">Thread safety</a>,
Next:&nbsp;<a rel="next" accesskey="n" href="#Numeric%20limits">Numeric limits</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#Character%20types">Character types</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#Top">Top</a>
<br>
</div>

<h2 class="chapter">Thread safety</h2>

<p>The C++ library string functionality requires a couple of atomic
operations to provide thread-safety.  If you don't take any special
action, the library will use stub versions of these functions that are
not thread-safe.  They will work fine, unless your applications are
multi-threaded.

   <p>If you want to provide custom, safe, versions of these functions, there
are two distinct approaches.  One is to provide a version for your CPU,
using assembly language constructs.  The other is to use the
thread-safety primitives in your operating system.  In either case, you
make a file called <code>atomicity.h</code>, and the variable
<code>ATOMICITYH</code> must point to this file.

   <p>If you are using the assembly-language approach, put this code in
<code>config/cpu/&lt;chip&gt;/atomicity.h</code>, where chip is the name of
your processor (see <a href="#CPU">CPU</a>).  No additional changes are necessary to
locate the file in this case; <code>ATOMICITYH</code> will be set by default.

   <p>If you are using the operating system thread-safety primitives approach,
you can also put this code in the same CPU directory, in which case no more
work is needed to locate the file.  For examples of this approach,
see the <code>atomicity.h</code> file for IRIX or IA64.

   <p>Alternatively, if the primitives are more closely related to the OS
than they are to the CPU, you can put the <code>atomicity.h</code> file in
the <a href="#Operating%20system">Operating system</a> directory instead.  In this case, you must
edit <code>configure.host</code>, and in the switch statement that handles
operating systems, override the <code>ATOMICITYH</code> variable to point to
the appropriate <code>os_include_dir</code>.  For examples of this approach,
see the <code>atomicity.h</code> file for AIX.

   <p>With those bits out of the way, you have to actually write
<code>atomicity.h</code> itself.  This file should be wrapped in an
include guard named <code>_GLIBCXX_ATOMICITY_H</code>.  It should define one
type, and two functions.

   <p>The type is <code>_Atomic_word</code>.  Here is the version used on IRIX:

<pre class="example">     typedef long _Atomic_word;
     </pre>

<p>This type must be a signed integral type supporting atomic operations. 
If you're using the OS approach, use the same type used by your system's
primitives.  Otherwise, use the type for which your CPU provides atomic
primitives.

   <p>Then, you must provide two functions.  The bodies of these functions
must be equivalent to those provided here, but using atomic operations:

<pre class="example">     static inline _Atomic_word
     __attribute__ ((__unused__))
     __exchange_and_add (_Atomic_word* __mem, int __val)
     {
       _Atomic_word __result = *__mem;
       *__mem += __val;
       return __result;
     }
     
     static inline void
     __attribute__ ((__unused__))
     __atomic_add (_Atomic_word* __mem, int __val)
     {
       *__mem += __val;
     }
     </pre>

<div class="node">
<p><hr>
Node:&nbsp;<a name="Numeric%20limits">Numeric limits</a>,
Next:&nbsp;<a rel="next" accesskey="n" href="#Libtool">Libtool</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#Thread%20safety">Thread safety</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#Top">Top</a>
<br>
</div>

<h2 class="chapter">Numeric limits</h2>

<p>The C++ library requires information about the fundamental data types,
such as the minimum and maximum representable values of each type. 
You can define each of these values individually, but it is usually
easiest just to indicate how many bits are used in each of the data
types and let the library do the rest.  For information about the
macros to define, see the top of <code>include/bits/std_limits.h</code>.

   <p>If you need to define any macros, you can do so in <code>os_defines.h</code>. 
However, if all operating systems for your CPU are likely to use the
same values, you can provide a CPU-specific file instead so that you
do not have to provide the same definitions for each operating system. 
To take that approach, create a new file called <code>cpu_limits.h</code> in
your CPU configuration directory (see <a href="#CPU">CPU</a>).

<div class="node">
<p><hr>
Node:&nbsp;<a name="Libtool">Libtool</a>,
Next:&nbsp;<a rel="next" accesskey="n" href="#GNU%20Free%20Documentation%20License">GNU Free Documentation License</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#Numeric%20limits">Numeric limits</a>,
Up:&nbsp;<a rel="up" accesskey="u" href="#Top">Top</a>
<br>
</div>

<h2 class="chapter">Libtool</h2>

<p>The C++ library is compiled, archived and linked with libtool. 
Explaining the full workings of libtool is beyond the scope of this
document, but there are a few, particular bits that are necessary for
porting.

   <p>Some parts of the libstdc++-v3 library are compiled with the libtool
<code>--tags CXX</code> option (the C++ definitions for libtool).  Therefore,
<code>ltcf-cxx.sh</code> in the top-level directory needs to have the correct
logic to compile and archive objects equivalent to the C version of libtool,
<code>ltcf-c.sh</code>.  Some libtool targets have definitions for C but not
for C++, or C++ definitions which have not been kept up to date.

   <p>The C++ run-time library contains initialization code that needs to be
run as the library is loaded.  Often, that requires linking in special
object files when the C++ library is built as a shared library, or
taking other system-specific actions.

   <p>The libstdc++-v3 library is linked with the C version of libtool, even
though it is a C++ library.  Therefore, the C version of libtool needs to
ensure that the run-time library initializers are run.  The usual way to
do this is to build the library using <code>gcc -shared</code>.

   <p>If you need to change how the library is linked, look at
<code>ltcf-c.sh</code> in the top-level directory.  Find the switch statement
that sets <code>archive_cmds</code>.  Here, adjust the setting for your
operating system.

<div class="node">
<p><hr>
Node:&nbsp;<a name="GNU%20Free%20Documentation%20License">GNU Free Documentation License</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="#Libtool">Libtool</a>,
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<br>
</div>

<h2 class="unnumbered">GNU Free Documentation License</h2>

<div align="center">Version 1.2, November 2002</div>
<pre class="display">     Copyright &copy; 2000,2001,2002 Free Software Foundation, Inc.
     59 Temple Place, Suite 330, Boston, MA  02111-1307, USA
     
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.
     </pre>

     <ol type=1 start=0>
<li>PREAMBLE

     <p>The purpose of this License is to make a manual, textbook, or other
functional and useful document <dfn>free</dfn> in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or noncommercially. 
Secondarily, this License preserves for the author and publisher a way
to get credit for their work, while not being considered responsible
for modifications made by others.

     <p>This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.  It
complements the GNU General Public License, which is a copyleft
license designed for free software.

     <p>We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free
program should come with manuals providing the same freedoms that the
software does.  But this License is not limited to software manuals;
it can be used for any textual work, regardless of subject matter or
whether it is published as a printed book.  We recommend this License
principally for works whose purpose is instruction or reference.

     </p><li>APPLICABILITY AND DEFINITIONS

     <p>This License applies to any manual or other work, in any medium, that
contains a notice placed by the copyright holder saying it can be
distributed under the terms of this License.  Such a notice grants a
world-wide, royalty-free license, unlimited in duration, to use that
work under the conditions stated herein.  The "Document", below,
refers to any such manual or work.  Any member of the public is a
licensee, and is addressed as "you".  You accept the license if you
copy, modify or distribute the work in a way requiring permission
under copyright law.

     <p>A "Modified Version" of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
modifications and/or translated into another language.

     <p>A "Secondary Section" is a named appendix or a front-matter section
of the Document that deals exclusively with the relationship of the
publishers or authors of the Document to the Document's overall
subject (or to related matters) and contains nothing that could fall
directly within that overall subject.  (Thus, if the Document is in
part a textbook of mathematics, a Secondary Section may not explain
any mathematics.)  The relationship could be a matter of historical
connection with the subject or with related matters, or of legal,
commercial, philosophical, ethical or political position regarding
them.

     <p>The "Invariant Sections" are certain Secondary Sections whose titles
are designated, as being those of Invariant Sections, in the notice
that says that the Document is released under this License.  If a
section does not fit the above definition of Secondary then it is not
allowed to be designated as Invariant.  The Document may contain zero
Invariant Sections.  If the Document does not identify any Invariant
Sections then there are none.

     <p>The "Cover Texts" are certain short passages of text that are listed,
as Front-Cover Texts or Back-Cover Texts, in the notice that says that
the Document is released under this License.  A Front-Cover Text may
be at most 5 words, and a Back-Cover Text may be at most 25 words.

     <p>A "Transparent" copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the
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for automatic translation to a variety of formats suitable for input
to text formatters.  A copy made in an otherwise Transparent file
format whose markup, or absence of markup, has been arranged to thwart
or discourage subsequent modification by readers is not Transparent. 
An image format is not Transparent if used for any substantial amount
of text.  A copy that is not "Transparent" is called "Opaque".

     <p>Examples of suitable formats for Transparent copies include plain
<small>ASCII</small> without markup, Texinfo input format, LaTeX input
format, <small>SGML</small> or <small>XML</small> using a publicly available
<small>DTD</small>, and standard-conforming simple <small>HTML</small>,
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of transparent image formats include <small>PNG</small>, <small>XCF</small> and
<small>JPG</small>.  Opaque formats include proprietary formats that can be
read and edited only by proprietary word processors, <small>SGML</small> or
<small>XML</small> for which the <small>DTD</small> and/or processing tools are
not generally available, and the machine-generated <small>HTML</small>,
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output purposes only.

     <p>The "Title Page" means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the material
this License requires to appear in the title page.  For works in
formats which do not have any title page as such, "Title Page" means
the text near the most prominent appearance of the work's title,
preceding the beginning of the body of the text.

     <p>A section "Entitled XYZ" means a named subunit of the Document whose
title either is precisely XYZ or contains XYZ in parentheses following
text that translates XYZ in another language.  (Here XYZ stands for a
specific section name mentioned below, such as "Acknowledgements",
"Dedications", "Endorsements", or "History".)  To "Preserve the Title"
of such a section when you modify the Document means that it remains a
section "Entitled XYZ" according to this definition.

     <p>The Document may include Warranty Disclaimers next to the notice which
states that this License applies to the Document.  These Warranty
Disclaimers are considered to be included by reference in this
License, but only as regards disclaiming warranties: any other
implication that these Warranty Disclaimers may have is void and has
no effect on the meaning of this License.

     </p><li>VERBATIM COPYING

     <p>You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License applies
to the Document are reproduced in all copies, and that you add no other
conditions whatsoever to those of this License.  You may not use
technical measures to obstruct or control the reading or further
copying of the copies you make or distribute.  However, you may accept
compensation in exchange for copies.  If you distribute a large enough
number of copies you must also follow the conditions in section 3.

     <p>You may also lend copies, under the same conditions stated above, and
you may publicly display copies.

     </p><li>COPYING IN QUANTITY

     <p>If you publish printed copies (or copies in media that commonly have
printed covers) of the Document, numbering more than 100, and the
Document's license notice requires Cover Texts, you must enclose the
copies in covers that carry, clearly and legibly, all these Cover
Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
the back cover.  Both covers must also clearly and legibly identify
you as the publisher of these copies.  The front cover must present
the full title with all words of the title equally prominent and
visible.  You may add other material on the covers in addition. 
Copying with changes limited to the covers, as long as they preserve
the title of the Document and satisfy these conditions, can be treated
as verbatim copying in other respects.

     <p>If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto adjacent
pages.

     <p>If you publish or distribute Opaque copies of the Document numbering
more than 100, you must either include a machine-readable Transparent
copy along with each Opaque copy, or state in or with each Opaque copy
a computer-network location from which the general network-using
public has access to download using public-standard network protocols
a complete Transparent copy of the Document, free of added material. 
If you use the latter option, you must take reasonably prudent steps,
when you begin distribution of Opaque copies in quantity, to ensure
that this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you distribute an
Opaque copy (directly or through your agents or retailers) of that
edition to the public.

     <p>It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give
them a chance to provide you with an updated version of the Document.

     </p><li>MODIFICATIONS

     <p>You may copy and distribute a Modified Version of the Document under
the conditions of sections 2 and 3 above, provided that you release
the Modified Version under precisely this License, with the Modified
Version filling the role of the Document, thus licensing distribution
and modification of the Modified Version to whoever possesses a copy
of it.  In addition, you must do these things in the Modified Version:

          <ol type=A start=1>
<li>Use in the Title Page (and on the covers, if any) a title distinct
from that of the Document, and from those of previous versions
(which should, if there were any, be listed in the History section
of the Document).  You may use the same title as a previous version
if the original publisher of that version gives permission.

          <li>List on the Title Page, as authors, one or more persons or entities
responsible for authorship of the modifications in the Modified
Version, together with at least five of the principal authors of the
Document (all of its principal authors, if it has fewer than five),
unless they release you from this requirement.

          <li>State on the Title page the name of the publisher of the
Modified Version, as the publisher.

          <li>Preserve all the copyright notices of the Document.

          <li>Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.

          <li>Include, immediately after the copyright notices, a license notice
giving the public permission to use the Modified Version under the
terms of this License, in the form shown in the Addendum below.

          <li>Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document's license notice.

          <li>Include an unaltered copy of this License.

          <li>Preserve the section Entitled "History", Preserve its Title, and add
to it an item stating at least the title, year, new authors, and
publisher of the Modified Version as given on the Title Page.  If
there is no section Entitled "History" in the Document, create one
stating the title, year, authors, and publisher of the Document as
given on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.

          <li>Preserve the network location, if any, given in the Document for
public access to a Transparent copy of the Document, and likewise
the network locations given in the Document for previous versions
it was based on.  These may be placed in the "History" section. 
You may omit a network location for a work that was published at
least four years before the Document itself, or if the original
publisher of the version it refers to gives permission.

          <li>For any section Entitled "Acknowledgements" or "Dedications", Preserve
the Title of the section, and preserve in the section all the
substance and tone of each of the contributor acknowledgements and/or
dedications given therein.

          <li>Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles.  Section numbers
or the equivalent are not considered part of the section titles.

          <li>Delete any section Entitled "Endorsements".  Such a section
may not be included in the Modified Version.

          <li>Do not retitle any existing section to be Entitled "Endorsements" or
to conflict in title with any Invariant Section.

          <li>Preserve any Warranty Disclaimers.
          </ol>

     <p>If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no material
copied from the Document, you may at your option designate some or all
of these sections as invariant.  To do this, add their titles to the
list of Invariant Sections in the Modified Version's license notice. 
These titles must be distinct from any other section titles.

     <p>You may add a section Entitled "Endorsements", provided it contains
nothing but endorsements of your Modified Version by various
parties--for example, statements of peer review or that the text has
been approved by an organization as the authoritative definition of a
standard.

     <p>You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list
of Cover Texts in the Modified Version.  Only one passage of
Front-Cover Text and one of Back-Cover Text may be added by (or
through arrangements made by) any one entity.  If the Document already
includes a cover text for the same cover, previously added by you or
by arrangement made by the same entity you are acting on behalf of,
you may not add another; but you may replace the old one, on explicit
permission from the previous publisher that added the old one.

     <p>The author(s) and publisher(s) of the Document do not by this License
give permission to use their names for publicity for or to assert or
imply endorsement of any Modified Version.

     </p><li>COMBINING DOCUMENTS

     <p>You may combine the Document with other documents released under this
License, under the terms defined in section 4 above for modified
versions, provided that you include in the combination all of the
Invariant Sections of all of the original documents, unmodified, and
list them all as Invariant Sections of your combined work in its
license notice, and that you preserve all their Warranty Disclaimers.

     <p>The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy.  If there are multiple Invariant Sections with the same name but
different contents, make the title of each such section unique by
adding at the end of it, in parentheses, the name of the original
author or publisher of that section if known, or else a unique number. 
Make the same adjustment to the section titles in the list of
Invariant Sections in the license notice of the combined work.

     <p>In the combination, you must combine any sections Entitled "History"
in the various original documents, forming one section Entitled
"History"; likewise combine any sections Entitled "Acknowledgements",
and any sections Entitled "Dedications".  You must delete all
sections Entitled "Endorsements."

     </p><li>COLLECTIONS OF DOCUMENTS

     <p>You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in
the collection, provided that you follow the rules of this License for
verbatim copying of each of the documents in all other respects.

     <p>You may extract a single document from such a collection, and distribute
it individually under this License, provided you insert a copy of this
License into the extracted document, and follow this License in all
other respects regarding verbatim copying of that document.

     </p><li>AGGREGATION WITH INDEPENDENT WORKS

     <p>A compilation of the Document or its derivatives with other separate
and independent documents or works, in or on a volume of a storage or
distribution medium, is called an "aggregate" if the copyright
resulting from the compilation is not used to limit the legal rights
of the compilation's users beyond what the individual works permit. 
When the Document is included an aggregate, this License does not
apply to the other works in the aggregate which are not themselves
derivative works of the Document.

     <p>If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half of
the entire aggregate, the Document's Cover Texts may be placed on
covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic form. 
Otherwise they must appear on printed covers that bracket the whole
aggregate.

     </p><li>TRANSLATION

     <p>Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section 4. 
Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections.  You may include a
translation of this License, and all the license notices in the
Document, and any Warrany Disclaimers, provided that you also include
the original English version of this License and the original versions
of those notices and disclaimers.  In case of a disagreement between
the translation and the original version of this License or a notice
or disclaimer, the original version will prevail.

     <p>If a section in the Document is Entitled "Acknowledgements",
"Dedications", or "History", the requirement (section 4) to Preserve
its Title (section 1) will typically require changing the actual
title.

     </p><li>TERMINATION

     <p>You may not copy, modify, sublicense, or distribute the Document except
as expressly provided for under this License.  Any other attempt to
copy, modify, sublicense or distribute the Document is void, and will
automatically terminate your rights under this License.  However,
parties who have received copies, or rights, from you under this
License will not have their licenses terminated so long as such
parties remain in full compliance.

     </p><li>FUTURE REVISIONS OF THIS LICENSE

     <p>The Free Software Foundation may publish new, revised versions
of the GNU Free Documentation License from time to time.  Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns.  See
<a href="http://www.gnu.org/copyleft/">http://www.gnu.org/copyleft/</a>.

     <p>Each version of the License is given a distinguishing version number. 
If the Document specifies that a particular numbered version of this
License "or any later version" applies to it, you have the option of
following the terms and conditions either of that specified version or
of any later version that has been published (not as a draft) by the
Free Software Foundation.  If the Document does not specify a version
number of this License, you may choose any version ever published (not
as a draft) by the Free Software Foundation.
        </ol>

<h3 class="unnumberedsec">ADDENDUM: How to use this License for your documents</h3>

<p>To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and
license notices just after the title page:

<pre class="smallexample">       Copyright (C)  <var>year</var>  <var>your name</var>.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
       A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.
     </pre>

   <p>If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the "with...Texts." line with this:

<pre class="smallexample">         with the Invariant Sections being <var>list their titles</var>, with
         the Front-Cover Texts being <var>list</var>, and with the Back-Cover Texts
         being <var>list</var>.
     </pre>

   <p>If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

   <p>If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License,
to permit their use in free software.


<div class="contents">
<h2>Table of Contents</h2>
<ul>
<li><a name="toc_Top" href="#Top">Porting libstdc++-v3</a>
<li><a name="toc_Operating%20system" href="#Operating%20system">Operating system</a>
<li><a name="toc_CPU" href="#CPU">CPU</a>
<li><a name="toc_Character%20types" href="#Character%20types">Character types</a>
<li><a name="toc_Thread%20safety" href="#Thread%20safety">Thread safety</a>
<li><a name="toc_Numeric%20limits" href="#Numeric%20limits">Numeric limits</a>
<li><a name="toc_Libtool" href="#Libtool">Libtool</a>
<li><a name="toc_GNU%20Free%20Documentation%20License" href="#GNU%20Free%20Documentation%20License">GNU Free Documentation License</a>
<ul>
<li><a href="#GNU%20Free%20Documentation%20License">ADDENDUM: How to use this License for your documents</a>
</li></ul>
</li></ul>
</div>

   </body></html>