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+/* Compile-time assert-like macros.
+
+   Copyright (C) 2005-2006, 2009-2011 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* Written by Paul Eggert, Bruno Haible, and Jim Meyering.  */
+
+#ifndef _GL_VERIFY_H
+# define _GL_VERIFY_H
+
+
+/* Define _GL_HAVE__STATIC_ASSERT to 1 if _Static_assert works as per the
+   C1X draft N1548 section 6.7.10.  This is supported by GCC 4.6.0 and
+   later, in C mode, and its use here generates easier-to-read diagnostics
+   when verify (R) fails.
+
+   Define _GL_HAVE_STATIC_ASSERT to 1 if static_assert works as per the
+   C++0X draft N3242 section 7.(4).
+   This will likely be supported by future GCC versions, in C++ mode.
+
+   Use this only with GCC.  If we were willing to slow 'configure'
+   down we could also use it with other compilers, but since this
+   affects only the quality of diagnostics, why bother?  */
+# if (4 < __GNUC__ || (__GNUC__ == 4 && 6 <= __GNUC_MINOR__)) && !defined __cplusplus
+#  define _GL_HAVE__STATIC_ASSERT 1
+# endif
+/* The condition (99 < __GNUC__) is temporary, until we know about the
+   first G++ release that supports static_assert.  */
+# if (99 < __GNUC__) && defined __cplusplus
+#  define _GL_HAVE_STATIC_ASSERT 1
+# endif
+
+/* Each of these macros verifies that its argument R is nonzero.  To
+   be portable, R should be an integer constant expression.  Unlike
+   assert (R), there is no run-time overhead.
+
+   If _Static_assert works, verify (R) uses it directly.  Similarly,
+   _GL_VERIFY_TRUE works by packaging a _Static_assert inside a struct
+   that is an operand of sizeof.
+
+   The code below uses several ideas for C++ compilers, and for C
+   compilers that do not support _Static_assert:
+
+   * The first step is ((R) ? 1 : -1).  Given an expression R, of
+     integral or boolean or floating-point type, this yields an
+     expression of integral type, whose value is later verified to be
+     constant and nonnegative.
+
+   * Next this expression W is wrapped in a type
+     struct _gl_verify_type {
+       unsigned int _gl_verify_error_if_negative: W;
+     }.
+     If W is negative, this yields a compile-time error.  No compiler can
+     deal with a bit-field of negative size.
+
+     One might think that an array size check would have the same
+     effect, that is, that the type struct { unsigned int dummy[W]; }
+     would work as well.  However, inside a function, some compilers
+     (such as C++ compilers and GNU C) allow local parameters and
+     variables inside array size expressions.  With these compilers,
+     an array size check would not properly diagnose this misuse of
+     the verify macro:
+
+       void function (int n) { verify (n < 0); }
+
+   * For the verify macro, the struct _gl_verify_type will need to
+     somehow be embedded into a declaration.  To be portable, this
+     declaration must declare an object, a constant, a function, or a
+     typedef name.  If the declared entity uses the type directly,
+     such as in
+
+       struct dummy {...};
+       typedef struct {...} dummy;
+       extern struct {...} *dummy;
+       extern void dummy (struct {...} *);
+       extern struct {...} *dummy (void);
+
+     two uses of the verify macro would yield colliding declarations
+     if the entity names are not disambiguated.  A workaround is to
+     attach the current line number to the entity name:
+
+       #define _GL_CONCAT0(x, y) x##y
+       #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y)
+       extern struct {...} * _GL_CONCAT (dummy, __LINE__);
+
+     But this has the problem that two invocations of verify from
+     within the same macro would collide, since the __LINE__ value
+     would be the same for both invocations.  (The GCC __COUNTER__
+     macro solves this problem, but is not portable.)
+
+     A solution is to use the sizeof operator.  It yields a number,
+     getting rid of the identity of the type.  Declarations like
+
+       extern int dummy [sizeof (struct {...})];
+       extern void dummy (int [sizeof (struct {...})]);
+       extern int (*dummy (void)) [sizeof (struct {...})];
+
+     can be repeated.
+
+   * Should the implementation use a named struct or an unnamed struct?
+     Which of the following alternatives can be used?
+
+       extern int dummy [sizeof (struct {...})];
+       extern int dummy [sizeof (struct _gl_verify_type {...})];
+       extern void dummy (int [sizeof (struct {...})]);
+       extern void dummy (int [sizeof (struct _gl_verify_type {...})]);
+       extern int (*dummy (void)) [sizeof (struct {...})];
+       extern int (*dummy (void)) [sizeof (struct _gl_verify_type {...})];
+
+     In the second and sixth case, the struct type is exported to the
+     outer scope; two such declarations therefore collide.  GCC warns
+     about the first, third, and fourth cases.  So the only remaining
+     possibility is the fifth case:
+
+       extern int (*dummy (void)) [sizeof (struct {...})];
+
+   * GCC warns about duplicate declarations of the dummy function if
+     -Wredundant_decls is used.  GCC 4.3 and later have a builtin
+     __COUNTER__ macro that can let us generate unique identifiers for
+     each dummy function, to suppress this warning.
+
+   * This implementation exploits the fact that older versions of GCC,
+     which do not support _Static_assert, also do not warn about the
+     last declaration mentioned above.
+
+   * In C++, any struct definition inside sizeof is invalid.
+     Use a template type to work around the problem.  */
+
+/* Concatenate two preprocessor tokens.  */
+# define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y)
+# define _GL_CONCAT0(x, y) x##y
+
+/* _GL_COUNTER is an integer, preferably one that changes each time we
+   use it.  Use __COUNTER__ if it works, falling back on __LINE__
+   otherwise.  __LINE__ isn't perfect, but it's better than a
+   constant.  */
+# if defined __COUNTER__ && __COUNTER__ != __COUNTER__
+#  define _GL_COUNTER __COUNTER__
+# else
+#  define _GL_COUNTER __LINE__
+# endif
+
+/* Generate a symbol with the given prefix, making it unique if
+   possible.  */
+# define _GL_GENSYM(prefix) _GL_CONCAT (prefix, _GL_COUNTER)
+
+/* Verify requirement R at compile-time, as an integer constant expression
+   that returns 1.  If R is false, fail at compile-time, preferably
+   with a diagnostic that includes the string-literal DIAGNOSTIC.  */
+
+# define _GL_VERIFY_TRUE(R, DIAGNOSTIC) \
+    (!!sizeof (_GL_VERIFY_TYPE (R, DIAGNOSTIC)))
+
+# ifdef __cplusplus
+#  if !GNULIB_defined_struct__gl_verify_type
+template <int w>
+  struct _gl_verify_type {
+    unsigned int _gl_verify_error_if_negative: w;
+  };
+#   define GNULIB_defined_struct__gl_verify_type 1
+#  endif
+#  define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
+    _gl_verify_type<(R) ? 1 : -1>
+# elif defined _GL_HAVE__STATIC_ASSERT
+#  define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
+     struct {                                   \
+       _Static_assert (R, DIAGNOSTIC);          \
+       int _gl_dummy;                          \
+     }
+# else
+#  define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
+     struct { unsigned int _gl_verify_error_if_negative: (R) ? 1 : -1; }
+# endif
+
+/* Verify requirement R at compile-time, as a declaration without a
+   trailing ';'.  If R is false, fail at compile-time, preferably
+   with a diagnostic that includes the string-literal DIAGNOSTIC.
+
+   Unfortunately, unlike C1X, this implementation must appear as an
+   ordinary declaration, and cannot appear inside struct { ... }.  */
+
+# ifdef _GL_HAVE__STATIC_ASSERT
+#  define _GL_VERIFY _Static_assert
+# else
+#  define _GL_VERIFY(R, DIAGNOSTIC)				       \
+     extern int (*_GL_GENSYM (_gl_verify_function) (void))	       \
+       [_GL_VERIFY_TRUE (R, DIAGNOSTIC)]
+# endif
+
+/* _GL_STATIC_ASSERT_H is defined if this code is copied into assert.h.  */
+# ifdef _GL_STATIC_ASSERT_H
+#  if !defined _GL_HAVE__STATIC_ASSERT && !defined _Static_assert
+#   define _Static_assert(R, DIAGNOSTIC) _GL_VERIFY (R, DIAGNOSTIC)
+#  endif
+#  if !defined _GL_HAVE_STATIC_ASSERT && !defined static_assert
+#   define static_assert _Static_assert /* Draft C1X requires this #define.  */
+#  endif
+# endif
+
+/* @assert.h omit start@  */
+
+/* Each of these macros verifies that its argument R is nonzero.  To
+   be portable, R should be an integer constant expression.  Unlike
+   assert (R), there is no run-time overhead.
+
+   There are two macros, since no single macro can be used in all
+   contexts in C.  verify_true (R) is for scalar contexts, including
+   integer constant expression contexts.  verify (R) is for declaration
+   contexts, e.g., the top level.  */
+
+/* Verify requirement R at compile-time, as an integer constant expression.
+   Return 1.  This is equivalent to verify_expr (R, 1).
+
+   verify_true is obsolescent; please use verify_expr instead.  */
+
+# define verify_true(R) _GL_VERIFY_TRUE (R, "verify_true (" #R ")")
+
+/* Verify requirement R at compile-time.  Return the value of the
+   expression E.  */
+
+# define verify_expr(R, E) \
+    (_GL_VERIFY_TRUE (R, "verify_expr (" #R ", " #E ")") ? (E) : (E))
+
+/* Verify requirement R at compile-time, as a declaration without a
+   trailing ';'.  */
+
+# define verify(R) _GL_VERIFY (R, "verify (" #R ")")
+
+/* @assert.h omit end@  */
+
+#endif