PR libstdc++/85494 use rdseed and rand_s in std::random_device

Add support for additional sources of randomness to std::random_device,
to allow using RDSEED for Intel CPUs and rand_s for Windows. When
supported these can be selected using the tokens "rdseed" and "rand_s".
For *-w64-mingw32 targets the "default" token will now use rand_s, and
for other i?86-*-* and x86_64-*-* targets it will try to use "rdseed"
first, then "rdrand", and finally "/dev/urandom".

To simplify the declaration of std::random_device in <bits/random.h> the
constructors now unconditionally call _M_init instead of _M_init_pretr1,
and the function call operator now unconditionally calls _M_getval. The
library code now decides whether _M_init and _M_getval should use a real
source of randomness or the mt19937 engine.

Existing code compiled against old libstdc++ headers will still call
_M_init_pretr1 and _M_getval_pretr1, but those functions now forward to
_M_init and _M_getval if a real source of randomness is available. This
means existing code compiled for mingw-w64 will start to use rand_s just
by linking to a new libstdc++.dll.

	* acinclude.m4 (GLIBCXX_CHECK_X86_RDSEED): Define macro to check if
	the assembler supports rdseed.
	* config.h.in: Regenerate.
	* configure: Regenerate.
	* configure.ac: Use GLIBCXX_CHECK_X86_RDSEED.
	* config/os/mingw32-w64/os_defines.h (_GLIBCXX_USE_CRT_RAND_S): Define.
	* doc/html/*: Regenerate.
	* doc/xml/manual/status_cxx2011.xml: Document new tokens.
	* include/bits/random.h (random_device::random_device()): Always call
	_M_init rather than _M_init_pretr1.
	(random_device::random_device(const string&)): Likewise.
	(random_device::operator()()): Always call _M_getval().
	(random_device::_M_file): Replace first member of union with an
	anonymous struct, with _M_file as its first member.
	* src/c++11/random.cc [_GLIBCXX_X86_RDRAND] (USE_RDRAND): Define.
	[_GLIBCXX_X86_RDSEED] (USE_RDSEED): Define.
	(USE_MT19937): Define if none of the above are defined.
	(USE_POSIX_FILE_IO): Define.
	(_M_strtoul): Remove.
	[USE_RDSEED] (__x86_rdseed): Define new function.
	[_GLIBCXX_USE_CRT_RAND_S] (__winxp_rand_s): Define new function.
	(random_device::_M_init(const string&)): Initialize new union members.
	Add support for "rdseed" and "rand_s" tokens. Decide what the
	"default" token does according to which USE_* macros are defined.
	[USE_POSIX_FILE_IO]: Store a file descriptor.
	[USE_MT19937]: Forward to _M_init_pretr1 instead.
	(random_device::_M_init_pretr1(const string&)) [USE_MT19937]: Inline
	code from _M_strtoul.
	[!USE_MT19937]: Call _M_init, transforming the old default token or
	numeric tokens to "default".
	(random_device::_M_fini()) [USE_POSIX_FILE_IO]: Use close not fclose.
	(random_device::_M_getval()): Use new union members to obtain a
	random number from the stored function pointer or file descriptor.
	[USE_MT19937]: Obtain a value from the mt19937 engine.
	(random_device::_M_getval_pretr1()): Call _M_getval().
	(random_device::_M_getentropy()) [USE_POSIX_FILE_IO]: Use _M_fd
	instead of fileno.
	[!USE_MT19937] (mersenne_twister): Do not instantiate when not needed.
	* testsuite/26_numerics/random/random_device/85494.cc: New test.

From-SVN: r271740

3 files changed, 87 insertions, 23 deletions

diff --git a/libstdc++-v3/doc/html/manual/appendix_contributing.html b/libstdc++-v3/doc/html/manual/appendix_contributing.html
index ca8ae87..7c7bd5a 100644
--- a/libstdc++-v3/doc/html/manual/appendix_contributing.html
+++ b/libstdc++-v3/doc/html/manual/appendix_contributing.html
@@ -26,7 +26,7 @@
 	  organization. In the USA, this national standards
 	  organization is
 	  <a class="link" href="https://www.ansi.org" target="_top">ANSI</a>.
-	  (And if you've already registered with them you can <a class="link" href="https://webstore.ansi.org/RecordDetail.aspx?sku=ISO%2fIEC+14882%3a2014" target="_top">buy
+	  (And if you've already registered with them you can <a class="link" href="https://webstore.ansi.org/Standards/ISO/ISOIEC148822014" target="_top">buy
 	  the standard on-line</a>.)
 	</p></li><li class="listitem"><p>
 	  The library working group bugs, and known defects, can
diff --git a/libstdc++-v3/doc/html/manual/status.html b/libstdc++-v3/doc/html/manual/status.html
index 3840019..398a9490 100644
--- a/libstdc++-v3/doc/html/manual/status.html
+++ b/libstdc++-v3/doc/html/manual/status.html
@@ -303,18 +303,38 @@ particular release.
       <code class="classname">minstd_rand0</code>.
    </p><p>
       <span class="emphasis"><em> 26.5.6 [rand.device] </em></span>
-      The default <code class="code">token</code> argument to the
-      <code class="classname">random_device</code> constructor is
-      <code class="literal">"default"</code>. Other valid arguments are
-      <code class="literal">"/dev/random"</code> and <code class="literal">"/dev/urandom"</code>,
-      which determine the character special file to read random bytes from.
-      The <code class="literal">"default"</code> token will read bytes from a hardware
-      RNG if available (currently this only supports the IA-32 RDRAND
-      instruction) otherwise it is equivalent to
-      <code class="literal">"/dev/urandom"</code>.
+      The <code class="code">token</code> parameter of the
+      <code class="classname">random_device</code> constructor can be used to select
+      a specific source of random bytes. The valid token values are shown
+      in the list below.
+      The default constructor uses the token <code class="literal">"default"</code>.
+      </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">"default"</code></span></dt><dd>
+          Select the first available source from the other entries below.
+          This is the only token that is always valid.
+        </dd><dt><span class="term"><code class="literal">"rand_s"</code></span></dt><dd>
+          Use the MSVCRT <code class="function">rand_s</code> function.
+          This token is only valid for mingw-w64 targets.
+        </dd><dt><span class="term"><code class="literal">"rdseed"</code>, </span><span class="term"><code class="literal">"rdrand"</code> or <code class="literal">"rdrnd"</code></span></dt><dd>
+          Use the IA-32 <code class="literal">RDSEED</code> or <code class="literal">RDRAND</code>
+          instruction to read from an on-chip hardware random number generator.
+          These tokens are only valid for x86 and x86_64 targets when both
+          the assembler and CPU support the corresponding instruction.
+        </dd><dt><span class="term"><code class="literal">"/dev/urandom"</code>, </span><span class="term"><code class="literal">"/dev/random"</code></span></dt><dd>
+          Use the named character special file to read random bytes from.
+          These tokens are only valid when the device files are present
+          and readable by the current user.
+        </dd><dt><span class="term"><code class="literal">"mt19937"</code>, </span><span class="term">seed value</span></dt><dd>
+          When no source of nondeterministic random numbers is available a
+          <code class="classname">mersenne_twister_engine</code> will be used.
+          An integer seed value can be used as the token and will be converted
+          to an <code class="code">unsigned long</code> using <code class="function">strtoul</code>.
+          These tokens are only valid when no other source of random bytes
+          is available.
+        </dd></dl></div><p>
       An exception of type <code class="classname">runtime_error</code> will be
-      thrown if a <code class="classname">random_device</code> object cannot open
-      or read from the source of random bytes.
+      thrown if a <code class="classname">random_device</code> object is constructed
+      with an invalid token, or if it cannot open or read from the source
+      of random bytes.
    </p><p>
       <span class="emphasis"><em>26.5.8.1 [rand.dist.general]</em></span>
       The algorithms used by the distributions should be documented here.
diff --git a/libstdc++-v3/doc/xml/manual/status_cxx2011.xml b/libstdc++-v3/doc/xml/manual/status_cxx2011.xml
index 0fa4bc0..9c25b8f 100644
--- a/libstdc++-v3/doc/xml/manual/status_cxx2011.xml
+++ b/libstdc++-v3/doc/xml/manual/status_cxx2011.xml
@@ -2682,18 +2682,62 @@ particular release.
 
    <para>
       <emphasis> 26.5.6 [rand.device] </emphasis>
-      The default <code>token</code> argument to the
-      <classname>random_device</classname> constructor is
-      <literal>"default"</literal>. Other valid arguments are
-      <literal>"/dev/random"</literal> and <literal>"/dev/urandom"</literal>,
-      which determine the character special file to read random bytes from.
-      The <literal>"default"</literal> token will read bytes from a hardware
-      RNG if available (currently this only supports the IA-32 RDRAND
-      instruction) otherwise it is equivalent to
-      <literal>"/dev/urandom"</literal>.
+      The <code>token</code> parameter of the
+      <classname>random_device</classname> constructor can be used to select
+      a specific source of random bytes. The valid token values are shown
+      in the list below.
+      The default constructor uses the token <literal>"default"</literal>.
+      <variablelist>
+      <varlistentry>
+        <term><literal>"default"</literal></term>
+        <listitem>
+          Select the first available source from the other entries below.
+          This is the only token that is always valid.
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term><literal>"rand_s"</literal></term>
+        <listitem>
+          Use the MSVCRT <function>rand_s</function> function.
+          This token is only valid for mingw-w64 targets.
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term><literal>"rdseed"</literal></term>
+        <term><literal>"rdrand"</literal> or <literal>"rdrnd"</literal></term>
+        <listitem>
+          Use the IA-32 <literal>RDSEED</literal> or <literal>RDRAND</literal>
+          instruction to read from an on-chip hardware random number generator.
+          These tokens are only valid for x86 and x86_64 targets when both
+          the assembler and CPU support the corresponding instruction.
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term><literal>"/dev/urandom"</literal></term>
+        <term><literal>"/dev/random"</literal></term>
+        <listitem>
+          Use the named character special file to read random bytes from.
+          These tokens are only valid when the device files are present
+          and readable by the current user.
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term><literal>"mt19937"</literal></term>
+        <term>seed value</term>
+        <listitem>
+          When no source of nondeterministic random numbers is available a
+          <classname>mersenne_twister_engine</classname> will be used.
+          An integer seed value can be used as the token and will be converted
+          to an <code>unsigned long</code> using <function>strtoul</function>.
+          These tokens are only valid when no other source of random bytes
+          is available.
+        </listitem>
+      </varlistentry>
+      </variablelist>
       An exception of type <classname>runtime_error</classname> will be
-      thrown if a <classname>random_device</classname> object cannot open
-      or read from the source of random bytes.
+      thrown if a <classname>random_device</classname> object is constructed
+      with an invalid token, or if it cannot open or read from the source
+      of random bytes.
    </para>
 
    <para>