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+/* ABI compatibility for lgamma functions.
+   Copyright (C) 2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef LGAMMA_COMPAT_H
+#define LGAMMA_COMPAT_H 1
+
+#include <shlib-compat.h>
+
+/* XSI POSIX requires lgamma to set signgam, but ISO C does not permit
+   this.  Namespace issues can be avoided if the functions set
+   __signgam and signgam is a weak alias, but this only works if both
+   signgam and __signgam were exported from the glibc version the
+   program was linked against.  Before glibc 2.23, lgamma functions
+   set signgam which was not a weak alias for __signgam, so old
+   binaries have dynamic symbols for signgam only and the versions of
+   lgamma used for old binaries must set both signgam and __signgam.
+   Those versions also do a check of _LIB_VERSION != _ISOC_ to match
+   old glibc.
+
+   Users of this file define USE_AS_COMPAT to 0 when building the main
+   version of lgamma, 1 when building the compatibility version.  */
+
+#define LGAMMA_OLD_VER GLIBC_2_0
+#define LGAMMA_NEW_VER GLIBC_2_23
+#define HAVE_LGAMMA_COMPAT SHLIB_COMPAT (libm, LGAMMA_OLD_VER, LGAMMA_NEW_VER)
+
+/* Whether to build this version at all.  */
+#define BUILD_LGAMMA (HAVE_LGAMMA_COMPAT || !USE_AS_COMPAT)
+
+/* The name to use for this version.  */
+#if USE_AS_COMPAT
+# define LGFUNC(FUNC) FUNC ## _compat
+#else
+# define LGFUNC(FUNC) FUNC
+#endif
+
+/* If there is a compatibility version, gamma (not an ISO C function,
+   so never a problem for it to set signgam) points directly to it
+   rather than having separate versions.  */
+#define GAMMA_ALIAS (USE_AS_COMPAT ? HAVE_LGAMMA_COMPAT : !HAVE_LGAMMA_COMPAT)
+
+/* How to call the underlying lgamma_r function.  */
+#define CALL_LGAMMA(TYPE, FUNC, ARG)			\
+  ({							\
+    TYPE lgamma_tmp;					\
+    int local_signgam;					\
+    if (USE_AS_COMPAT)					\
+      {							\
+	lgamma_tmp = FUNC ((ARG), &local_signgam);	\
+	if (_LIB_VERSION != _ISOC_)			\
+	  signgam = __signgam = local_signgam;		\
+      }							\
+    else						\
+      lgamma_tmp = FUNC ((ARG), &__signgam);		\
+    lgamma_tmp;						\
+  })
+
+#endif /* lgamma-compat.h.  */