/* Compile-time assert-like macros.
- Copyright (C) 2005-2006, 2009-2010 Free Software Foundation, Inc.
+ Copyright (C) 2005-2006, 2009-2014 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
/* Written by Paul Eggert, Bruno Haible, and Jim Meyering. */
-#ifndef VERIFY_H
-# define VERIFY_H 1
+#ifndef _GL_VERIFY_H
+#define _GL_VERIFY_H
+
+
+/* Define _GL_HAVE__STATIC_ASSERT to 1 if _Static_assert works as per C11.
+ 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 C++11.
+ 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__ + (6 <= __GNUC_MINOR__) \
+ && (201112L <= __STDC_VERSION__ || !defined __STRICT_ANSI__) \
+ && !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
+
+/* 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.
- 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.
-
- Symbols ending in "__" are private to this header.
+ 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.
+ 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
constant and nonnegative.
* Next this expression W is wrapped in a type
- struct verify_type__ { unsigned int verify_error_if_negative_size__: W; }.
+ 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.
void function (int n) { verify (n < 0); }
- * For the verify macro, the struct verify_type__ will need to
+ * 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,
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__);
+ #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.
+ 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
Which of the following alternatives can be used?
extern int dummy [sizeof (struct {...})];
- extern int dummy [sizeof (struct verify_type__ {...})];
+ extern int dummy [sizeof (struct _gl_verify_type {...})];
extern void dummy (int [sizeof (struct {...})]);
- extern void dummy (int [sizeof (struct verify_type__ {...})]);
+ extern void dummy (int [sizeof (struct _gl_verify_type {...})]);
extern int (*dummy (void)) [sizeof (struct {...})];
- extern int (*dummy (void)) [sizeof (struct verify_type__ {...})];
+ 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
extern int (*dummy (void)) [sizeof (struct {...})];
- * This implementation exploits the fact that GCC does not warn about
- the last declaration mentioned above. If a future version of GCC
- introduces a warning for this, the problem could be worked around
- by using code specialized to GCC, e.g.,:
+ * 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.
- #if 4 <= __GNUC__
- # define verify(R) \
- extern int (* verify_function__ (void)) \
- [__builtin_constant_p (R) && (R) ? 1 : -1]
- #endif
+ * 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
-/* Verify requirement R at compile-time, as an integer constant expression.
- Return 1. */
+/* Generate a symbol with the given prefix, making it unique if
+ possible. */
+#define _GL_GENSYM(prefix) _GL_CONCAT (prefix, _GL_COUNTER)
-# ifdef __cplusplus
+/* 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 verify_type__ { unsigned int verify_error_if_negative_size__: w; };
-# define verify_true(R) \
- (!!sizeof (verify_type__<(R) ? 1 : -1>))
-# else
-# define verify_true(R) \
- (!!sizeof \
- (struct { unsigned int verify_error_if_negative_size__: (R) ? 1 : -1; }))
+ 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 C11, 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 /* C11 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) extern int (* verify_function__ (void)) [verify_true (R)]
+#define verify(R) _GL_VERIFY (R, "verify (" #R ")")
+
+#ifndef __has_builtin
+# define __has_builtin(x) 0
+#endif
+
+/* Assume that R always holds. This lets the compiler optimize
+ accordingly. R should not have side-effects; it may or may not be
+ evaluated. Behavior is undefined if R is false. */
+
+#if (__has_builtin (__builtin_unreachable) \
+ || 4 < __GNUC__ + (5 <= __GNUC_MINOR__))
+# define assume(R) ((R) ? (void) 0 : __builtin_unreachable ())
+#elif 1200 <= _MSC_VER
+# define assume(R) __assume (R)
+#elif (defined lint \
+ && (__has_builtin (__builtin_trap) \
+ || 3 < __GNUC__ + (3 < __GNUC_MINOR__ + (4 <= __GNUC_PATCHLEVEL__))))
+ /* 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
+# define assume(R) ((void) (0 && (R)))
+#endif
+
+/* @assert.h omit end@ */
#endif
HCoop / bpt / guile.git / blobdiff