Annotation of embedaddon/libiconv/srclib/verify.h, revision 1.1.1.1
1.1 misho 1: /* Compile-time assert-like macros.
2:
3: Copyright (C) 2005-2006, 2009-2011 Free Software Foundation, Inc.
4:
5: This program is free software: you can redistribute it and/or modify
6: it under the terms of the GNU General Public License as published by
7: the Free Software Foundation; either version 3 of the License, or
8: (at your option) any later version.
9:
10: This program is distributed in the hope that it will be useful,
11: but WITHOUT ANY WARRANTY; without even the implied warranty of
12: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13: GNU General Public License for more details.
14:
15: You should have received a copy of the GNU General Public License
16: along with this program. If not, see <http://www.gnu.org/licenses/>. */
17:
18: /* Written by Paul Eggert, Bruno Haible, and Jim Meyering. */
19:
20: #ifndef _GL_VERIFY_H
21: # define _GL_VERIFY_H
22:
23:
24: /* Define _GL_HAVE__STATIC_ASSERT to 1 if _Static_assert works as per the
25: C1X draft N1548 section 6.7.10. This is supported by GCC 4.6.0 and
26: later, in C mode, and its use here generates easier-to-read diagnostics
27: when verify (R) fails.
28:
29: Define _GL_HAVE_STATIC_ASSERT to 1 if static_assert works as per the
30: C++0X draft N3242 section 7.(4).
31: This will likely be supported by future GCC versions, in C++ mode.
32:
33: Use this only with GCC. If we were willing to slow 'configure'
34: down we could also use it with other compilers, but since this
35: affects only the quality of diagnostics, why bother? */
36: # if (4 < __GNUC__ || (__GNUC__ == 4 && 6 <= __GNUC_MINOR__)) && !defined __cplusplus
37: # define _GL_HAVE__STATIC_ASSERT 1
38: # endif
39: /* The condition (99 < __GNUC__) is temporary, until we know about the
40: first G++ release that supports static_assert. */
41: # if (99 < __GNUC__) && defined __cplusplus
42: # define _GL_HAVE_STATIC_ASSERT 1
43: # endif
44:
45: /* Each of these macros verifies that its argument R is nonzero. To
46: be portable, R should be an integer constant expression. Unlike
47: assert (R), there is no run-time overhead.
48:
49: If _Static_assert works, verify (R) uses it directly. Similarly,
50: _GL_VERIFY_TRUE works by packaging a _Static_assert inside a struct
51: that is an operand of sizeof.
52:
53: The code below uses several ideas for C++ compilers, and for C
54: compilers that do not support _Static_assert:
55:
56: * The first step is ((R) ? 1 : -1). Given an expression R, of
57: integral or boolean or floating-point type, this yields an
58: expression of integral type, whose value is later verified to be
59: constant and nonnegative.
60:
61: * Next this expression W is wrapped in a type
62: struct _gl_verify_type {
63: unsigned int _gl_verify_error_if_negative: W;
64: }.
65: If W is negative, this yields a compile-time error. No compiler can
66: deal with a bit-field of negative size.
67:
68: One might think that an array size check would have the same
69: effect, that is, that the type struct { unsigned int dummy[W]; }
70: would work as well. However, inside a function, some compilers
71: (such as C++ compilers and GNU C) allow local parameters and
72: variables inside array size expressions. With these compilers,
73: an array size check would not properly diagnose this misuse of
74: the verify macro:
75:
76: void function (int n) { verify (n < 0); }
77:
78: * For the verify macro, the struct _gl_verify_type will need to
79: somehow be embedded into a declaration. To be portable, this
80: declaration must declare an object, a constant, a function, or a
81: typedef name. If the declared entity uses the type directly,
82: such as in
83:
84: struct dummy {...};
85: typedef struct {...} dummy;
86: extern struct {...} *dummy;
87: extern void dummy (struct {...} *);
88: extern struct {...} *dummy (void);
89:
90: two uses of the verify macro would yield colliding declarations
91: if the entity names are not disambiguated. A workaround is to
92: attach the current line number to the entity name:
93:
94: #define _GL_CONCAT0(x, y) x##y
95: #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y)
96: extern struct {...} * _GL_CONCAT (dummy, __LINE__);
97:
98: But this has the problem that two invocations of verify from
99: within the same macro would collide, since the __LINE__ value
100: would be the same for both invocations. (The GCC __COUNTER__
101: macro solves this problem, but is not portable.)
102:
103: A solution is to use the sizeof operator. It yields a number,
104: getting rid of the identity of the type. Declarations like
105:
106: extern int dummy [sizeof (struct {...})];
107: extern void dummy (int [sizeof (struct {...})]);
108: extern int (*dummy (void)) [sizeof (struct {...})];
109:
110: can be repeated.
111:
112: * Should the implementation use a named struct or an unnamed struct?
113: Which of the following alternatives can be used?
114:
115: extern int dummy [sizeof (struct {...})];
116: extern int dummy [sizeof (struct _gl_verify_type {...})];
117: extern void dummy (int [sizeof (struct {...})]);
118: extern void dummy (int [sizeof (struct _gl_verify_type {...})]);
119: extern int (*dummy (void)) [sizeof (struct {...})];
120: extern int (*dummy (void)) [sizeof (struct _gl_verify_type {...})];
121:
122: In the second and sixth case, the struct type is exported to the
123: outer scope; two such declarations therefore collide. GCC warns
124: about the first, third, and fourth cases. So the only remaining
125: possibility is the fifth case:
126:
127: extern int (*dummy (void)) [sizeof (struct {...})];
128:
129: * GCC warns about duplicate declarations of the dummy function if
130: -Wredundant_decls is used. GCC 4.3 and later have a builtin
131: __COUNTER__ macro that can let us generate unique identifiers for
132: each dummy function, to suppress this warning.
133:
134: * This implementation exploits the fact that older versions of GCC,
135: which do not support _Static_assert, also do not warn about the
136: last declaration mentioned above.
137:
138: * In C++, any struct definition inside sizeof is invalid.
139: Use a template type to work around the problem. */
140:
141: /* Concatenate two preprocessor tokens. */
142: # define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y)
143: # define _GL_CONCAT0(x, y) x##y
144:
145: /* _GL_COUNTER is an integer, preferably one that changes each time we
146: use it. Use __COUNTER__ if it works, falling back on __LINE__
147: otherwise. __LINE__ isn't perfect, but it's better than a
148: constant. */
149: # if defined __COUNTER__ && __COUNTER__ != __COUNTER__
150: # define _GL_COUNTER __COUNTER__
151: # else
152: # define _GL_COUNTER __LINE__
153: # endif
154:
155: /* Generate a symbol with the given prefix, making it unique if
156: possible. */
157: # define _GL_GENSYM(prefix) _GL_CONCAT (prefix, _GL_COUNTER)
158:
159: /* Verify requirement R at compile-time, as an integer constant expression
160: that returns 1. If R is false, fail at compile-time, preferably
161: with a diagnostic that includes the string-literal DIAGNOSTIC. */
162:
163: # define _GL_VERIFY_TRUE(R, DIAGNOSTIC) \
164: (!!sizeof (_GL_VERIFY_TYPE (R, DIAGNOSTIC)))
165:
166: # ifdef __cplusplus
167: # if !GNULIB_defined_struct__gl_verify_type
168: template <int w>
169: struct _gl_verify_type {
170: unsigned int _gl_verify_error_if_negative: w;
171: };
172: # define GNULIB_defined_struct__gl_verify_type 1
173: # endif
174: # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
175: _gl_verify_type<(R) ? 1 : -1>
176: # elif defined _GL_HAVE__STATIC_ASSERT
177: # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
178: struct { \
179: _Static_assert (R, DIAGNOSTIC); \
180: int _gl_dummy; \
181: }
182: # else
183: # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
184: struct { unsigned int _gl_verify_error_if_negative: (R) ? 1 : -1; }
185: # endif
186:
187: /* Verify requirement R at compile-time, as a declaration without a
188: trailing ';'. If R is false, fail at compile-time, preferably
189: with a diagnostic that includes the string-literal DIAGNOSTIC.
190:
191: Unfortunately, unlike C1X, this implementation must appear as an
192: ordinary declaration, and cannot appear inside struct { ... }. */
193:
194: # ifdef _GL_HAVE__STATIC_ASSERT
195: # define _GL_VERIFY _Static_assert
196: # else
197: # define _GL_VERIFY(R, DIAGNOSTIC) \
198: extern int (*_GL_GENSYM (_gl_verify_function) (void)) \
199: [_GL_VERIFY_TRUE (R, DIAGNOSTIC)]
200: # endif
201:
202: /* _GL_STATIC_ASSERT_H is defined if this code is copied into assert.h. */
203: # ifdef _GL_STATIC_ASSERT_H
204: # if !defined _GL_HAVE__STATIC_ASSERT && !defined _Static_assert
205: # define _Static_assert(R, DIAGNOSTIC) _GL_VERIFY (R, DIAGNOSTIC)
206: # endif
207: # if !defined _GL_HAVE_STATIC_ASSERT && !defined static_assert
208: # define static_assert _Static_assert /* Draft C1X requires this #define. */
209: # endif
210: # endif
211:
212: /* @assert.h omit start@ */
213:
214: /* Each of these macros verifies that its argument R is nonzero. To
215: be portable, R should be an integer constant expression. Unlike
216: assert (R), there is no run-time overhead.
217:
218: There are two macros, since no single macro can be used in all
219: contexts in C. verify_true (R) is for scalar contexts, including
220: integer constant expression contexts. verify (R) is for declaration
221: contexts, e.g., the top level. */
222:
223: /* Verify requirement R at compile-time, as an integer constant expression.
224: Return 1. This is equivalent to verify_expr (R, 1).
225:
226: verify_true is obsolescent; please use verify_expr instead. */
227:
228: # define verify_true(R) _GL_VERIFY_TRUE (R, "verify_true (" #R ")")
229:
230: /* Verify requirement R at compile-time. Return the value of the
231: expression E. */
232:
233: # define verify_expr(R, E) \
234: (_GL_VERIFY_TRUE (R, "verify_expr (" #R ", " #E ")") ? (E) : (E))
235:
236: /* Verify requirement R at compile-time, as a declaration without a
237: trailing ';'. */
238:
239: # define verify(R) _GL_VERIFY (R, "verify (" #R ")")
240:
241: /* @assert.h omit end@ */
242:
243: #endif
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