mdw@git.distorted.org.uk Git - mLib/blob - utils/macros.h

   1 /* -*-c-*-
   2  *
   3  * Handy macros
   4  *
   5  * (c) 2003 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of the mLib utilities library.
  11  *
  12  * mLib is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU Library General Public License as
  14  * published by the Free Software Foundation; either version 2 of the
  15  * License, or (at your option) any later version.
  16  *
  17  * mLib is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with mLib; if not, write to the Free
  24  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 #ifndef MLIB_MACROS_H
  29 #define MLIB_MACROS_H
  30
  31 #ifdef __cplusplus
  32   extern "C" {
  33 #endif
  34
  35 /*----- Header files ------------------------------------------------------*/
  36
  37 #include <assert.h>
  38
  39 #ifndef MLIB_COMPILER_H
  40 #  include "compiler.h"
  41 #endif
  42
  43 /*----- Miscellaneous utility macros --------------------------------------*/
  44
  45 /* --- @N@ --- *
  46  *
  47  * Arguments:   @type v[]@ = an actual array, not a pointer
  48  *
  49  * Returns:     The number of elements in @v@.
  50  */
  51
  52 #define N(v) (sizeof(v)/sizeof(*(v)))
  53
  54 /* --- @STR@ --- *
  55  *
  56  * Arguments:   @x@ = some tokens
  57  *
  58  * Returns:     A string literal containing the macro-expanded text of @x@.
  59  */
  60
  61 #define MLIB__STR(x) #x
  62 #define STR(x) MLIB__STR(x)
  63
  64 /* --- @GLUE@ --- *
  65  *
  66  * Arguments:   @x, y@ = two sequences of tokens
  67  *
  68  * Returns:     A single token formed by gluing together the macro-expansions
  69  *              of @x@ and @y@.
  70  */
  71
  72 #define MLIB__GLUE(x, y) x##y
  73 #define GLUE(x, y) MLIB__GLUE(x, y)
  74
  75 /* --- @STATIC_ASSERT@ --- *
  76  *
  77  * Arguments:   @int cond@ = a condition
  78  *              @msg@ = a string literal message
  79  *
  80  * Returns:     ---
  81  *
  82  * Use:         Fail at compile time unless @cond@ is nonzero.  The failure
  83  *              might report @msg@.
  84  */
  85
  86 #ifdef static_assert
  87 #  define STATIC_ASSERT(cond, msg) static_assert(!!(cond), msg)
  88 #else
  89 #  define STATIC_ASSERT(cond, msg)                                      \
  90         IGNORABLE extern char static_assert_failed[1 - 2*!(cond)]
  91 #endif
  92
  93 /* --- @CHECK_TYPE@ ---
  94  *
  95  * Arguments:   @expty@ = expected type of @x@
  96  *              @expty x@ = some object
  97  *
  98  * Returns:     Integer zero.
  99  *
 100  * Use:         Cause a compile-time failure unless the type of @x@ is
 101  *              assignment-compatible with @expty@.
 102  */
 103
 104 #define CHECK_TYPE(expty, x) (!sizeof(*(expty *)0 = (x)))
 105
 106 /* --- @CONVERT_CAREFULLY@ ---
 107  *
 108  * Arguments:   @newty@ = new type for the result
 109  *              @expty@ = expected type of @x@
 110  *              @expty x@ = some object
 111  *
 112  * Returns:     @x@, but coerced to type @newty@.
 113  *
 114  * Use:         Like @(newty)x@, except that it checks at compile-time that
 115  *              @x@ is at least assignment-compatible with type @expty@
 116  *              before trying.
 117  */
 118
 119 #define CONVERT_CAREFULLY(newty, expty, x)                              \
 120         (CHECK_TYPE(expty, x) + (/*unconst unvolatile*/ newty)(x))
 121
 122 /* --- @UNCONST@, @UNVOLATILE@, @UNQUALIFY@ --- *
 123  *
 124  * Arguments:   @type@ = a type name
 125  *              @type *p@ = a pointer
 126  *
 127  * Returns:     @p@, but without @const@, @volatile@ or both qualifiers.
 128  *
 129  * Use:         Strips qualifiers from pointer types.
 130  *
 131  *              The @UNCONST@ macro strips @const@.  It checks that @p@
 132  *              has type `pointer to @type@ or @const type@'; if not, a
 133  *              compile-time error results.  Otherwise, it returns the value
 134  *              of @p@, converted to `pointer to (non-constant) @type@'.  It
 135  *              will not silently strip a @volatile@ qualifier.
 136  *
 137  *              The @UNVOLATILE@ macro is similar, except that it strips
 138  *              @volatile@ instead of @const@.  The @UNQUALIFY@ macro strips
 139  *              both qualifiers.
 140  */
 141
 142 #define UNCONST(type, p) CONVERT_CAREFULLY(type *, const type *, p)
 143 #define UNVOLATILE(type, p) CONVERT_CAREFULLY(type *, volatile type *, p)
 144 #define UNQUALIFY(type, p)                                              \
 145         CONVERT_CAREFULLY(type *, const volatile type *, p)
 146
 147 /* --- @COMMA@ --- *
 148  *
 149  * Arguments:   ---
 150  *
 151  * Returns:     A `%|,|%' token, which can be usefully passed to macros to
 152  *              avoid argument splitting.
 153  */
 154
 155 #define COMMA ,
 156
 157 /*----- String and character hacks ----------------------------------------*/
 158
 159 /* --- @IS...@ --- *
 160  *
 161  * Arguments:   @int ch@ = a character code, but not @EOF@
 162  *
 163  * Returns:     Nonzero if @ch@ is in the relevant @<ctype.h>@ category.
 164  *
 165  * Use:         Classifies characters, but safely even if characters are
 166  *              signed.
 167  *
 168  *              There is a macro for each of the @<ctype.h>@ @is...@
 169  *              functions.
 170  */
 171
 172 #define CTYPE_HACK(func, ch) (func((unsigned char)(ch)))
 173
 174 #define ISALNUM(ch) CTYPE_HACK(isalnum, ch)
 175 #define ISALPHA(ch) CTYPE_HACK(isalpha, ch)
 176 #define ISASCII(ch) CTYPE_HACK(isascii, ch)
 177 #define ISBLANK(ch) CTYPE_HACK(isblank, ch)
 178 #define ISCNTRL(ch) CTYPE_HACK(iscntrl, ch)
 179 #define ISDIGIT(ch) CTYPE_HACK(isdigit, ch)
 180 #define ISGRAPH(ch) CTYPE_HACK(isgraph, ch)
 181 #define ISLOWER(ch) CTYPE_HACK(islower, ch)
 182 #define ISPRINT(ch) CTYPE_HACK(isprint, ch)
 183 #define ISPUNCT(ch) CTYPE_HACK(ispunct, ch)
 184 #define ISSPACE(ch) CTYPE_HACK(isspace, ch)
 185 #define ISUPPER(ch) CTYPE_HACK(isupper, ch)
 186 #define ISXDIGIT(ch) CTYPE_HACK(isxdigit, ch)
 187
 188 /* --- @TO...@ --- *
 189  *
 190  * Arguments:   @int ch@ = a character code, but not @EOF@
 191  *
 192  * Returns:     The converted character code.
 193  *
 194  * Use:         Converts characters, but safely even if characters are
 195  *              signed.
 196  *
 197  *              There is a macro for each of the @<ctype.h>@ @to...@
 198  *              functions.
 199  */
 200
 201 #define TOASCII(ch) CTYPE_HACK(toascii, ch)
 202 #define TOLOWER(ch) CTYPE_HACK(tolower, ch)
 203 #define TOUPPER(ch) CTYPE_HACK(toupper, ch)
 204
 205 /* --- @MEMCMP@, @STRCMP@, @STRNCMP@ --- *
 206  *
 207  * Arguments:   @const type *x, *y@ = pointers to strings
 208  *              @op@ = a relational operator symbol
 209  *              @size_t n@ = length of the strings
 210  *
 211  * Returns:     Nonzero if the relationship between the strings satisfies the
 212  *              operator @op@, otherwise zero.
 213  *
 214  * Use:         These macros mitigate the author's frequent error of failing
 215  *              to compare the result of the underlying standard functions
 216  *              against zero, effectively reversing the sense of an intended
 217  *              test for equality.
 218  */
 219
 220 #define MEMCMP(x, op, y, n) (memcmp((x), (y), (n)) op 0)
 221 #define STRCMP(x, op, y) (strcmp((x), (y)) op 0)
 222 #define STRNCMP(x, op, y, n) (strncmp((x), (y), (n)) op 0)
 223
 224 /*----- Compiler-specific definitions -------------------------------------*/
 225
 226 /* The descriptions of these are given below, with the fallback
 227  * definitions.
 228  */
 229
 230 #if GCC_VERSION_P(2, 5) || CLANG_VERSION_P(3, 3)
 231 #  define NORETURN __attribute__((__noreturn__))
 232 #  define PRINTF_LIKE(fix, aix) __attribute__((__format__(printf, fix, aix)))
 233 #  define SCANF_LIKE(fix, aix) __attribute__((__format__(scanf, fix, aix)))
 234 #  define IGNORABLE __attribute__((__unused__))
 235 #endif
 236
 237 #if GCC_VERSION_P(3, 4) || CLANG_VERSION_P(3, 3)
 238 #  define MUST_CHECK __attribute__((__warn_unused_result__))
 239 #endif
 240
 241 #if GCC_VERSION_P(4, 5) || CLANG_VERSION_P(3, 3)
 242 #  define DEPRECATED(msg) __attribute__((__deprecated__(msg)))
 243 #elif GCC_VERSION_P(3, 1)
 244 #  define DEPRECATED(msg) __attribute__((__deprecated__))
 245 #endif
 246
 247 #if GCC_VERSION_P(4, 0) || CLANG_VERSION_P(3, 3)
 248 #  define EXECL_LIKE(ntrail) __attribute__((__sentinel__(ntrail)))
 249 #endif
 250
 251 #if GCC_VERSION_P(2, 7) || CLANG_VERSION_P(0, 0)
 252 #  define LAUNDER(x)                                                    \
 253         ({ __typeof__(x) _y; __asm__("" : "=g"(_y) : "0"(x)); _y; })
 254 #  define ADMIRE(x)                                                     \
 255         ({ __asm__("" : : "g"(x)); })
 256 #  define ADMIRE_BUF(p, sz)                                             \
 257         ({ __asm__("" : : "g"(p), "g"(sz)); })
 258 #  define RELAX do __asm__ __volatile__("" ::: "memory"); while (0)
 259 #endif
 260
 261 #if CLANG_VERSION_P(3, 3)
 262
 263 #  define MLIB__PRAGMA_HACK(x) _Pragma(#x)
 264 #  define MLIB__MUFFLE_WARNINGS(warns, body)                            \
 265         _Pragma("clang diagnostic push")                                \
 266         warns                                                           \
 267         body                                                            \
 268         _Pragma("clang diagnostic pop")
 269 #  define CLANG_WARNING(warn)                                           \
 270         MLIB__PRAGMA_HACK(clang diagnostic ignored warn)
 271 #  define MUFFLE_WARNINGS_DECL(warns, body)                             \
 272         MLIB__MUFFLE_WARNINGS(warns, body)
 273 #  define MUFFLE_WARNINGS_EXPR(warns, body)                             \
 274         __extension__ ({ MLIB__MUFFLE_WARNINGS(warns, (body);) })
 275 #  define MUFFLE_WARNINGS_STMT(warns, body)                             \
 276         do { MLIB__MUFFLE_WARNINGS(warns, body) } while (0)
 277
 278 #endif
 279
 280 #if GCC_VERSION_P(4, 6)
 281
 282    /* --- Diagnostic suppression in GCC: a tale of woe --- *
 283     *
 284     * This is extremely unpleasant, largely as a result of bugs in the GCC
 285     * preprocessor's handling of @_Pragma@.  The fundamental problem is
 286     * that it's the preprocessor, and not the compiler proper, which
 287     * detects @_Pragma@, emitting @#pragma@ lines into its output; and it
 288     * does it during macro expansion, even if the macro is being expanded
 289     * during argument collection.  Since arguments are expanded before
 290     * replacing the macro's invocation with its body, a pragma in an
 291     * argument will be emitted %%\emph{before}%% any pragmata in the body,
 292     * even if they appear before the argument in the body -- and even if
 293     * the argument doesn't actually appear anywhere at all in the body.
 294     *
 295     * Another, rather less significant, problem is that @_Pragma@'s
 296     * argument is a single string literal, recognized in translation phase
 297     * 4, before string-literal concatenation in phase 6, so we must build
 298     * pragma bodies as token lists and then stringify them.
 299     *
 300     * As a result, we need some subterfuge here.  The @MLIB__PRAGMA_HACK@
 301     * macro issues a @_Pragma@ on its argument token list, which it
 302     * stringifies; this deals with the second problem.  The first is
 303     * trickier: we must delay expansion of @MLIB__PRAGMA_HACK@ from the
 304     * argument collection phase to the body rescanning phase, and we do
 305     * this by splitting the invocations between @GCC_WARNING@ macro calls:
 306     * the name is left hanging from the previous call (or from
 307     * @MLIB__MUFFLE_WARNINGS@, in the first case) and the body is supplied
 308     * by @GCC_WARNING@, which also supplies the next @MLIB__PRAGMA_HACK@.
 309     * The remaining problem is to make sure we can dispose of the final
 310     * trailing @MLIB__PRAGMA_HACK@ harmlessly, which we do by introducing
 311     * an extra argument @emitp@, which may be either @t@ or @nil@; this
 312     * dispatches to an appropriate helper macro by means of token-pasting.
 313     *
 314     * I'm so sorry.
 315     */
 316
 317 #  define MLIB__PRAGMA_HACK_t(x) _Pragma(#x)
 318 #  define MLIB__PRAGMA_HACK_nil(x)
 319 #  define MLIB__PRAGMA_HACK(emitp, x) MLIB__PRAGMA_HACK_##emitp(x)
 320 #  define MLIB__MUFFLE_WARNINGS(warns, body)                            \
 321         _Pragma("GCC diagnostic push") MLIB__PRAGMA_HACK                \
 322         warns                                                           \
 323         (nil, nil)                                                      \
 324         body                                                            \
 325         _Pragma("GCC diagnostic pop")
 326 #  define GCC_WARNING(warn)                                             \
 327         (t, GCC diagnostic ignored warn) MLIB__PRAGMA_HACK
 328 #  define MUFFLE_WARNINGS_DECL(warns, body)                             \
 329         MLIB__MUFFLE_WARNINGS(warns, body)
 330 #  define MUFFLE_WARNINGS_EXPR(warns, body)                             \
 331         __extension__ ({ MLIB__MUFFLE_WARNINGS(warns, (body);) })
 332 #  define MUFFLE_WARNINGS_STMT(warns, body)                             \
 333         do { MLIB__MUFFLE_WARNINGS(warns, body) } while (0)
 334 #endif
 335
 336 /* --- Fallback definitions, mostly trivial --- */
 337
 338 /* --- @DISCARD@ --- *
 339  *
 340  * Arguments:   @x@ = a function call
 341  *
 342  * Returns:     ---
 343  *
 344  * Use:         Explicitly discard the result of @x@.  This counteracts a
 345  *              @MUST_CHECK@ attribute on the called function.
 346  */
 347
 348 #ifndef DISCARD
 349 #  define DISCARD(x) do if (x); while (0)
 350 #endif
 351
 352 /* --- @IGNORE@ --- *
 353  *
 354  * Arguments:   @x@ = any expression
 355  *
 356  * Returns:     ---
 357  *
 358  * Use:         Ignore the value of @x@, overriding compiler warnings.
 359  */
 360
 361 #ifndef IGNORE
 362 #  define IGNORE(x) ((void)(x))
 363 #endif
 364
 365 /* --- @LAUNDER@ --- *
 366  *
 367  * Arguments:   @x@ = some integer expression
 368  *
 369  * Returns:     @x@.
 370  *
 371  * Use:         Causes a compiler to know nothing about the value of @x@,
 372  *              even if it looks obvious, e.g., it's a constant.
 373  */
 374
 375 #ifndef LAUNDER
 376 #  define LAUNDER(x) (x)
 377 #endif
 378
 379 /* --- @ADMIRE@, @ADMIRE_BUF@ --- *
 380  *
 381  * Arguments:   @x@ = some scalar expression
 382  *              @const void *p@, @size_t sz@ = a pointer and length
 383  *
 384  * Returns:     ---
 385  *
 386  * Use:         Ensures that the compiler generates code to compute @x@ or
 387  *              the contents of the buffer at @p@.
 388  */
 389
 390 #ifndef ADMIRE
 391 #  define ADMIRE(x) ((void)(x))
 392 #endif
 393 #ifndef ADMIRE_BUF
 394 #  define ADMIRE_BUF(p, sz) ((void)(p), (void)(sz))
 395 #endif
 396
 397 /* --- @RELAX@ --- *
 398  *
 399  * Arguments:   ---
 400  *
 401  * Returns:     ---
 402  *
 403  * Use:         Does nothing, but the compiler doesn't know that.
 404  */
 405
 406 #ifndef RELAX
 407 #  define RELAX
 408 #endif
 409
 410 /* --- @DEPRECATED@, @NORETURN@, @IGNORABLE@, @MUST_CHECK@ --- *
 411  *
 412  * Use:         These are (mostly) function attributes; write them among the
 413  *              declaration specifiers for a function definition or
 414  *              declaration.  These may not do anything, but the intended
 415  *              behaviour is as follows.
 416  *
 417  *                * @DEPRECATED(msg)@ -- report a warning, quoting the string
 418  *                  literal @msg@, if the function is called.
 419  *
 420  *                * @NORETURN@ -- promise that the function doesn't return to
 421  *                  its caller: either it kills the process, or it performs
 422  *                  some nonlocal transfer.
 423  *
 424  *                * @IGNORABLE@ -- the item (which might be data rather than
 425  *                  a function) might not be referred to, but that's OK:
 426  *                  don't warn about it.
 427  *
 428  *                @ @MUST_CHECK@ -- warn if the return value of a function is
 429  *                  ignored.  Use @DISCARD@ if you really don't care.
 430  */
 431
 432 #ifndef DEPRECATED
 433 #  define DEPRECATED(msg)
 434 #endif
 435
 436 #ifndef NORETURN
 437 #  define NORETURN
 438 #endif
 439
 440 #ifndef IGNORABLE
 441 #  define IGNORABLE
 442 #endif
 443
 444 #ifndef MUST_CHECK
 445 #  define MUST_CHECK
 446 #endif
 447
 448 /* --- @PRINTF_LIKE@, @SCANF_LIKE@, @EXECL_LIKE@ --- *
 449  *
 450  * Arguments:   @int fmtix@ = format string argument index (starting from 1)
 451  *              @int argix@ = variable format argument tail index (starting
 452  *                      from 1)
 453  *              @int ntrail@ = number of arguments following terminator
 454  *
 455  * Use:         These are function attributes.  Again, they might not do
 456  *              anything at all.  By intention, they give the compiler
 457  *              information about a variadic function's arguments, so that it
 458  *              can warn about misuse.
 459  *
 460  *                * @PRINTF_LIKE@ -- the function takes a @printf@-style
 461  *                  format string as argument @fmtix@ and an argument tail
 462  *                  (which may be empty) beginning with argument @argix@.
 463  *
 464  *                * @SCANF_LIKE@ -- the function takes a @scanf@-style
 465  *                  format string as argument @fmtix@ and an argument tail
 466  *                  (which may be empty) beginning with argument @argix@.
 467  *
 468  *                * @EXECL_LIKE@ -- the function takes a sequence of pointer
 469  *                  arguments terminated by a null pointer, followed by
 470  *                  @ntrail@ further arguments.
 471  */
 472
 473 #ifndef PRINTF_LIKE
 474 #  define PRINF_LIKE(fmtix, argix)
 475 #endif
 476
 477 #ifndef SCANF_LIKE
 478 #  define SCANF_LIKE(fmtix, argix)
 479 #endif
 480
 481 #ifndef EXECL_LIKE
 482 #  define EXECL_LIKE(ntrail)
 483 #endif
 484
 485 /* --- @MUFFLE_WARNINGS_...@ --- *
 486  *
 487  * Arguments:   @warns@ = a sequence of @..._WARNING@ calls (see below)
 488  *              @body@ = some program text
 489  *
 490  * Use:         Muffle specific warnings within the program text.
 491  *
 492  *              For @MUFFLE_WARNINGS_DECL@, the program text is a
 493  *              declaration; for @MUFFLE_WARNINGS_EXPR@, it is an expression,
 494  *              and for @MUFFLE_WARNINGS_STMT@, it is a statement.
 495  *
 496  *              The warnings to be muffled are given as a list of
 497  *              @..._WARNING@ macros, with no separators.  The list can
 498  *              list warnings from multiple different compilers: entries for
 499  *              irrelevant compilers will be ignored.
 500  */
 501
 502 #ifndef MUFFLE_WARNINGS_DECL
 503 #  define MUFFLE_WARNINGS_DECL(warns, body) body
 504 #endif
 505
 506 #ifndef MUFFLE_WARNINGS_EXPR
 507 #  define MUFFLE_WARNINGS_EXPR(warns, body) (body)
 508 #endif
 509
 510 #ifndef MUFFLE_WARNINGS_STMT
 511 #  define MUFFLE_WARNINGS_STMT(warns, body) do { body } while (0)
 512 #endif
 513
 514 /* --- @GCC_WARNING@ --- *
 515  *
 516  * Arguments:   @warn@ = a string literal naming a warning, with `%|-W...|%'
 517  *                      prefix
 518  *
 519  * Use:         Names a GCC warning: use within @MUFFLE_WARNINGS_...@.
 520  *
 521  *              Note that GCC's warning suppression is very buggy.
 522  */
 523
 524 #ifndef GCC_WARNING
 525 #  define GCC_WARNING(warn)
 526 #endif
 527
 528 /* --- @CLANG_WARNING@ --- *
 529  *
 530  * Arguments:   @warn@ = a string literal naming a warning, with `%|-W...|%'
 531  *                      prefix
 532  *
 533  * Use:         Names a Clang warning: use within @MUFFLE_WARNINGS_...@.
 534  */
 535
 536 #ifndef CLANG_WARNING
 537 #  define CLANG_WARNING(warn)
 538 #endif
 539
 540 /*----- That's all, folks -------------------------------------------------*/
 541
 542 #ifdef __cplusplus
 543   }
 544 #endif
 545
 546 #endif