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+/* Compile-time assert-like macros.
+
+ Copyright (C) 2005-2006, 2009-2022 Free Software Foundation, Inc.
+
+ This file 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.
+
+ This file 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 this program. If not, see <https://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 (R, DIAGNOSTIC)
+ works as per C11. This is supported by GCC 4.6.0+ and by clang 4+.
+
+ Define _GL_HAVE__STATIC_ASSERT1 to 1 if _Static_assert (R) works as
+ per C2x. This is supported by GCC 9.1+.
+
+ Support compilers claiming conformance to the relevant standard,
+ and also support GCC when not pedantic. 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? */
+#ifndef __cplusplus
+# if (201112L <= __STDC_VERSION__ \
+ || (!defined __STRICT_ANSI__ \
+ && (4 < __GNUC__ + (6 <= __GNUC_MINOR__) || 4 <= __clang_major__)))
+# define _GL_HAVE__STATIC_ASSERT 1
+# endif
+# if (202000L <= __STDC_VERSION__ \
+ || (!defined __STRICT_ANSI__ && 9 <= __GNUC__))
+# define _GL_HAVE__STATIC_ASSERT1 1
+# endif
+#endif
+
+/* FreeBSD 9.1 <sys/cdefs.h>, included by <stddef.h> and lots of other
+ system headers, defines a conflicting _Static_assert that is no
+ better than ours; override it. */
+#ifndef _GL_HAVE__STATIC_ASSERT
+# include <stddef.h>
+# undef _Static_assert
+#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.
+
+ * GCC warns if -Wnested-externs is enabled and 'verify' is used
+ within a function body; but inside a function, you can always
+ arrange to use verify_expr instead.
+
+ * 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.
+
+ This macro requires three or more arguments but uses at most the first
+ two, so that the _Static_assert macro optionally defined below supports
+ both the C11 two-argument syntax and the C2x one-argument syntax.
+
+ Unfortunately, unlike C11, this implementation must appear as an
+ ordinary declaration, and cannot appear inside struct { ... }. */
+
+#if 200410 <= __cpp_static_assert
+# define _GL_VERIFY(R, DIAGNOSTIC, ...) static_assert (R, DIAGNOSTIC)
+#elif defined _GL_HAVE__STATIC_ASSERT
+# define _GL_VERIFY(R, DIAGNOSTIC, ...) _Static_assert (R, DIAGNOSTIC)
+#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_ASSERT1 && !defined _Static_assert
+# define _Static_assert(...) \
+ _GL_VERIFY (__VA_ARGS__, "static assertion failed", -)
+# endif
+# if __cpp_static_assert < 201411 && !defined static_assert
+# define static_assert _Static_assert /* C11 requires this #define. */
+# endif
+#endif
+
+/* @assert.h omit start@ */
+
+#if 3 < __GNUC__ + (3 < __GNUC_MINOR__ + (4 <= __GNUC_PATCHLEVEL__))
+# define _GL_HAS_BUILTIN_TRAP 1
+#elif defined __has_builtin
+# define _GL_HAS_BUILTIN_TRAP __has_builtin (__builtin_trap)
+#else
+# define _GL_HAS_BUILTIN_TRAP 0
+#endif
+
+#if 4 < __GNUC__ + (5 <= __GNUC_MINOR__)
+# define _GL_HAS_BUILTIN_UNREACHABLE 1
+#elif defined __has_builtin
+# define _GL_HAS_BUILTIN_UNREACHABLE __has_builtin (__builtin_unreachable)
+#else
+# define _GL_HAS_BUILTIN_UNREACHABLE 0
+#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.
+
+ There are two macros, since no single macro can be used in all
+ contexts in C. verify_expr (R, E) 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. 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 ';'. verify (R) acts like static_assert (R) except that
+ it is portable to C11/C++14 and earlier, it can issue better
+ diagnostics, and its name is shorter and may be more convenient. */
+
+#ifdef __PGI
+/* PGI barfs if R is long. */
+# define verify(R) _GL_VERIFY (R, "verify (...)", -)
+#else
+# define verify(R) _GL_VERIFY (R, "verify (" #R ")", -)
+#endif
+
+/* Assume that R always holds. Behavior is undefined if R is false,
+ fails to evaluate, or has side effects.
+
+ 'assume (R)' is a directive from the programmer telling the
+ compiler that R is true so the compiler needn't generate code to
+ test R. This is why 'assume' is in verify.h: it's related to
+ static checking (in this case, static checking done by the
+ programmer), not dynamic checking.
+
+ 'assume (R)' can affect compilation of all the code, not just code
+ that happens to be executed after the assume (R) is "executed".
+ For example, if the code mistakenly does 'assert (R); assume (R);'
+ the compiler is entitled to optimize away the 'assert (R)'.
+
+ Although assuming R can help a compiler generate better code or
+ diagnostics, performance can suffer if R uses hard-to-optimize
+ features such as function calls not inlined by the compiler.
+
+ Avoid Clang's __builtin_assume, as it breaks GNU Emacs master
+ as of 2020-08-23T21:09:49Z!eggert@cs.ucla.edu; see
+ <https://bugs.gnu.org/43152#71>. It's not known whether this breakage
+ is a Clang bug or an Emacs bug; play it safe for now. */
+
+#if _GL_HAS_BUILTIN_UNREACHABLE
+# define assume(R) ((R) ? (void) 0 : __builtin_unreachable ())
+#elif 1200 <= _MSC_VER
+# define assume(R) __assume (R)
+#elif (defined GCC_LINT || defined lint) && _GL_HAS_BUILTIN_TRAP
+ /* Doing it this way helps various packages when configured with
+ --enable-gcc-warnings, which compiles with -Dlint. It's nicer
+ when 'assume' silences warnings even with older GCCs. */
+# define assume(R) ((R) ? (void) 0 : __builtin_trap ())
+#else
+ /* Some tools grok NOTREACHED, e.g., Oracle Studio 12.6. */
+# define assume(R) ((R) ? (void) 0 : /*NOTREACHED*/ (void) 0)
+#endif
+
+/* @assert.h omit end@ */
+
+#endif