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Annotation of coherent/f/usr/include/common/feature.h, revision 1.1

1.1     ! root        1: #ifndef        __COMMON_FEATURE_H__
        !             2: #define        __COMMON_FEATURE_H__
        !             3: 
        !             4: /*
        !             5:  * This header file deals with some minor complications that exist in the
        !             6:  * world of feature-tests. Standard style for new code is to use the simpler
        !             7:  * and more powerful #if test rather than the cumbersome and less useful
        !             8:  * #ifdef/#ifndef tests that untutored programmers gravitate to.
        !             9:  *
        !            10:  * However, this is made more difficult by historical problems, and some
        !            11:  * latitude extended to users. For example, while POSIX.1 introduces a
        !            12:  * feature-test macro such as _POSIX_SOURCE, no value for this macro was
        !            13:  * recommended, and so users typically #define this symbol to have no value,
        !            14:  * making the #if form of feature-test more complex. Conversely, the ISO C
        !            15:  * standard mandates a value for __STDC__, but users have uniformly ignored
        !            16:  * this fact.
        !            17:  *
        !            18:  * This file mutates definitions of well-known feature tests so that the #if
        !            19:  * form of test can be used universally. This means using several tricks to
        !            20:  * detect such things as symbols with empty values, but such tricks break down
        !            21:  * if users are perverse and #define symbols like _POSIX_SOURCE with values
        !            22:  * that are strings or which cannot be evaluated. For such symbols, we have
        !            23:  * an option which will simply force the feature to value 1 rather than trying
        !            24:  * to be clever. This means that some utility is lost (in the sense that
        !            25:  * features cannot have graduated values for purposes such as selecting
        !            26:  * versions) so this is off by default.
        !            27:  */
        !            28: 
        !            29: #define        __EMPTY(x)              ((1 - x - 1) == 2)
        !            30: 
        !            31: #define        __UNDEFINED_OR_EMPTY(x) (! defined (x) || __EMPTY (x))
        !            32: 
        !            33: #ifdef _FORCE_TO_ONE
        !            34: # undef                _FORCE_TO_ONE
        !            35: # define       _FORCE_TO_ONE   1
        !            36: #endif
        !            37: 
        !            38: #if    defined (_POSIX_SOURCE)
        !            39: # if   _FORCE_TO_ONE
        !            40: 
        !            41: #  undef       _POSIX_SOURCE
        !            42: #  define      _POSIX_SOURCE   1
        !            43: 
        !            44: # elif __EMPTY (_POSIX_SOURCE)
        !            45: 
        !            46: #  undef       _POSIX_SOURCE
        !            47: #  define      _POSIX_SOURCE   1
        !            48: 
        !            49: #endif
        !            50: #endif
        !            51: 
        !            52: 
        !            53: 
        !            54: /*
        !            55:  * We have a feature-test _STDC_SOURCE analagous to _POSIX_SOURCE which
        !            56:  * selects a minimal ISO C compilation environment. This is mutually exclusive
        !            57:  * with _POSIX_SOURCE. We could either complain or do something tricky like
        !            58:  * select the one with the highest value.
        !            59:  */
        !            60: 
        !            61: #if    _STDC_SOUCE || _POSIX_SOURCE
        !            62: # if   _STDC_SOURCE > _POSIX_SOURCE
        !            63: 
        !            64: #  undef       _POSIX_SOURCE
        !            65: 
        !            66: # elif _STDC_SOURCE < _POSIX_SOURCE
        !            67: 
        !            68: #  undef       _STDC_SOURCE
        !            69: 
        !            70: # else
        !            71: 
        !            72: #  error You cannot select both _POSIX_SOURCE and _STDC_SOURCE in a compilation
        !            73: 
        !            74: # endif
        !            75: #endif
        !            76: 
        !            77: /*
        !            78:  * For Coherent: avoid the use of COHERENT as a feature-test, use __COHERENT__
        !            79:  * instead.
        !            80:  */
        !            81: 
        !            82: #ifdef KERNEL
        !            83: 
        !            84: #undef KERNEL
        !            85: #undef __KERNEL__
        !            86: #define        __KERNEL__      1
        !            87: 
        !            88: #endif
        !            89: 
        !            90: #ifdef COHERENT
        !            91: 
        !            92: #undef __COHERENT__
        !            93: #define        __COHERENT__    1
        !            94: 
        !            95: #endif
        !            96: 
        !            97: /*
        !            98:  * The MWC port of GCC botches -ansi mode by not defining _I386; here we put
        !            99:  * it back in again. This also serves to define _I386 for those systems that
        !           100:  * traditionally just define "i386".
        !           101:  */
        !           102: 
        !           103: #if    __GNUC__ && (defined (i386) || __COHERENT__) && ! defined (_I386)
        !           104: # define       _I386   1
        !           105: #endif
        !           106: 
        !           107: #endif /* ! defined (__COMMON_FEATURE_H__) */

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