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+// Copyright (c) 1999, 2007, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: Ray Sidney and many others
+//
+// Defines the VLOG_IS_ON macro that controls the variable-verbosity
+// conditional logging.
+//
+// It's used by VLOG and VLOG_IF in logging.h
+// and by RAW_VLOG in raw_logging.h to trigger the logging.
+//
+// It can also be used directly e.g. like this:
+//   if (VLOG_IS_ON(2)) {
+//     // do some logging preparation and logging
+//     // that can't be accomplished e.g. via just VLOG(2) << ...;
+//   }
+//
+// The truth value that VLOG_IS_ON(level) returns is determined by 
+// the three verbosity level flags:
+//   --v=<n>  Gives the default maximal active V-logging level;
+//            0 is the default.
+//            Normally positive values are used for V-logging levels.
+//   --vmodule=<str>  Gives the per-module maximal V-logging levels to override
+//                    the value given by --v.
+//                    E.g. "my_module=2,foo*=3" would change the logging level
+//                    for all code in source files "my_module.*" and "foo*.*"
+//                    ("-inl" suffixes are also disregarded for this matching).
+//
+// SetVLOGLevel helper function is provided to do limited dynamic control over
+// V-logging by overriding the per-module settings given via --vmodule flag.
+//
+// CAVEAT: --vmodule functionality is not available in non gcc compilers.
+//
+
+#ifndef BASE_VLOG_IS_ON_H_
+#define BASE_VLOG_IS_ON_H_
+
+#include "glog/log_severity.h"
+
+// Annoying stuff for windows -- makes sure clients can import these functions
+#ifndef GOOGLE_GLOG_DLL_DECL
+# if defined(_WIN32) && !defined(__CYGWIN__)
+#   define GOOGLE_GLOG_DLL_DECL  __declspec(dllimport)
+# else
+#   define GOOGLE_GLOG_DLL_DECL
+# endif
+#endif
+
+#if defined(__GNUC__)
+// We emit an anonymous static int* variable at every VLOG_IS_ON(n) site.
+// (Normally) the first time every VLOG_IS_ON(n) site is hit,
+// we determine what variable will dynamically control logging at this site:
+// it's either FLAGS_v or an appropriate internal variable
+// matching the current source file that represents results of
+// parsing of --vmodule flag and/or SetVLOGLevel calls.
+#define VLOG_IS_ON(verboselevel)                                \
+  __extension__  \
+  ({ static @ac_google_namespace@::int32* vlocal__ = &@ac_google_namespace@::kLogSiteUninitialized;           \
+     @ac_google_namespace@::int32 verbose_level__ = (verboselevel);                    \
+     (*vlocal__ >= verbose_level__) &&                          \
+     ((vlocal__ != &@ac_google_namespace@::kLogSiteUninitialized) ||                   \
+      (@ac_google_namespace@::InitVLOG3__(&vlocal__, &FLAGS_v,                         \
+                   __FILE__, verbose_level__))); })
+#else
+// GNU extensions not available, so we do not support --vmodule.
+// Dynamic value of FLAGS_v always controls the logging level.
+#define VLOG_IS_ON(verboselevel) (FLAGS_v >= (verboselevel))
+#endif
+
+// Set VLOG(_IS_ON) level for module_pattern to log_level.
+// This lets us dynamically control what is normally set by the --vmodule flag.
+// Returns the level that previously applied to module_pattern.
+// NOTE: To change the log level for VLOG(_IS_ON) sites
+//	 that have already executed after/during InitGoogleLogging,
+//	 one needs to supply the exact --vmodule pattern that applied to them.
+//       (If no --vmodule pattern applied to them
+//       the value of FLAGS_v will continue to control them.)
+extern GOOGLE_GLOG_DLL_DECL int SetVLOGLevel(const char* module_pattern,
+                                             int log_level);
+
+// Various declarations needed for VLOG_IS_ON above: =========================
+
+// Special value used to indicate that a VLOG_IS_ON site has not been
+// initialized.  We make this a large value, so the common-case check
+// of "*vlocal__ >= verbose_level__" in VLOG_IS_ON definition
+// passes in such cases and InitVLOG3__ is then triggered.
+extern @ac_google_namespace@::int32 kLogSiteUninitialized;
+
+// Helper routine which determines the logging info for a particalur VLOG site.
+//   site_flag     is the address of the site-local pointer to the controlling
+//                 verbosity level
+//   site_default  is the default to use for *site_flag
+//   fname         is the current source file name
+//   verbose_level is the argument to VLOG_IS_ON
+// We will return the return value for VLOG_IS_ON
+// and if possible set *site_flag appropriately.
+extern GOOGLE_GLOG_DLL_DECL bool InitVLOG3__(
+    @ac_google_namespace@::int32** site_flag,
+    @ac_google_namespace@::int32* site_default,
+    const char* fname,
+    @ac_google_namespace@::int32 verbose_level);
+
+#endif  // BASE_VLOG_IS_ON_H_