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Annotation of embedaddon/bird2/lib/macro.h, revision 1.1.1.1

1.1       misho       1: /* 
                      2:  *     BIRD Macro Tricks
                      3:  *
                      4:  *     (c) 2018 Jan Maria Matejka <mq@jmq.cz>
                      5:  *
                      6:  *     Can be freely distributed and used under the terms of the GNU GPL.
                      7:  *
                      8:  *     Contains useful but dirty macro tricks:
                      9:  *             MACRO_CONCAT(a, b)      -> concatenates a##b
                     10:  *             MACRO_BOOL(x)           -> convert 0 to 0, anything else to 1
                     11:  *             MACRO_IFELSE(b)(true-branch)(false-branch)
                     12:  *                                     -> b shall be 0 or 1; expands to the appropriate branch
                     13:  *             MACRO_ISEMPTY(...)      -> 1 for empty argument list, 0 otherwise
                     14:  *             MACRO_FOREACH(func, ...)
                     15:  *                                     -> calling FOREACH(func, a, b, c, d) expands to
                     16:  *                                             func(a) func(b) func(c) func(d)
                     17:  *             MACRO_RPACK(func, terminator, ...)
                     18:  *                                     -> packs the list into recursive calls:
                     19:  *                                             func(func(func(func(terminator, a), b), c), d)
                     20:  */
                     21: 
                     22: #ifndef _BIRD_MACRO_H_
                     23: #define _BIRD_MACRO_H_
                     24: 
                     25: /* What to do with args */
                     26: #define MACRO_DROP(...)
                     27: #define MACRO_UNPAREN(...) __VA_ARGS__
                     28: #define MACRO_SEP(a, b, sep)  a sep b
                     29: 
                     30: /* Aliases for some special chars */
                     31: #define MACRO_COMMA ,
                     32: #define MACRO_LPAREN (
                     33: #define MACRO_RPAREN )
                     34: #define MACRO_LPAREN_() (
                     35: #define MACRO_RPAREN_() )
                     36: 
                     37: /* Multiple expansion trick */
                     38: #define MACRO_EXPAND0(...) __VA_ARGS__
                     39: #define MACRO_EXPAND1(...) MACRO_EXPAND0(MACRO_EXPAND0(__VA_ARGS__))
                     40: #define MACRO_EXPAND2(...) MACRO_EXPAND1(MACRO_EXPAND1(__VA_ARGS__))
                     41: #define MACRO_EXPAND3(...) MACRO_EXPAND2(MACRO_EXPAND2(__VA_ARGS__))
                     42: #define MACRO_EXPAND(...) MACRO_EXPAND3(MACRO_EXPAND3(__VA_ARGS__))
                     43: 
                     44: /* Deferring expansion in the expansion trick */
                     45: #define MACRO_EMPTY()
                     46: #define MACRO_DEFER(t) t MACRO_EMPTY()
                     47: #define MACRO_DEFER2(t) t MACRO_EMPTY MACRO_EMPTY()()
                     48: #define MACRO_DEFER3(t) t MACRO_EMPTY MACRO_EMPTY MACRO_EMPTY()()()
                     49: 
                     50: /* Token concatenation */
                     51: #define MACRO_CONCAT(prefix, ...) prefix##__VA_ARGS__
                     52: #define MACRO_CONCAT_AFTER(...) MACRO_CONCAT(__VA_ARGS__)
                     53: 
                     54: /* Get first or second argument only */
                     55: #define MACRO_FIRST(a, ...) a
                     56: #define MACRO_SECOND(a, b, ...) b
                     57: #define MACRO_SECOND_OR_ZERO(...) MACRO_SECOND(__VA_ARGS__, 0,)
                     58: 
                     59: /* Macro Boolean auxiliary macros */
                     60: #define MACRO_BOOL_CHECK_0 ~, 1
                     61: #define MACRO_BOOL_NEG(x) MACRO_SECOND_OR_ZERO(MACRO_CONCAT(MACRO_BOOL_CHECK_, x))
                     62: 
                     63: #define MACRO_BOOL_NOT_0  1
                     64: #define MACRO_BOOL_NOT_1  0
                     65: 
                     66: /* Macro Boolean negation */
                     67: #define MACRO_NOT(x) MACRO_CONCAT(MACRO_BOOL_NOT_, x)
                     68: 
                     69: /* Convert anything to bool (anything -> 1, 0 -> 0) */
                     70: #define MACRO_BOOL(x) MACRO_NOT(MACRO_BOOL_NEG(x))
                     71: 
                     72: /*
                     73:  * Macro If/Else condition
                     74:  * Usage: MACRO_IFELSE(condition)(true-branch)(false-branch)
                     75:  * Expands to true-branch if condition is true, otherwise to false-branch.
                     76:  */
                     77: #define MACRO_IFELSE(b) MACRO_CONCAT(MACRO_IFELSE_, b)
                     78: #define MACRO_IFELSE_0(...) MACRO_UNPAREN
                     79: #define MACRO_IFELSE_1(...) __VA_ARGS__ MACRO_DROP
                     80: 
                     81: /* Auxiliary macros for MACRO_FOREACH */
                     82: #define MACRO_ISLAST(...) MACRO_BOOL_NEG(MACRO_FIRST(MACRO_ISLAST_CHECK __VA_ARGS__)())
                     83: #define MACRO_ISLAST_CHECK() 0
                     84: 
                     85: #define MACRO_FOREACH_EXPAND(call, a, ...) MACRO_IFELSE(MACRO_ISLAST(__VA_ARGS__))(call(a))(call(a) MACRO_DEFER2(MACRO_FOREACH_PAREN)()(call, __VA_ARGS__))
                     86: #define MACRO_FOREACH_PAREN() MACRO_FOREACH_EXPAND
                     87: 
                     88: #define MACRO_RPACK_EXPAND(call, terminator, a, ...) MACRO_IFELSE(MACRO_ISLAST(__VA_ARGS__))(call(terminator, a))(call(MACRO_DEFER2(MACRO_RPACK_PAREN)()(call, terminator, __VA_ARGS__), a))
                     89: #define MACRO_RPACK_PAREN() MACRO_RPACK_EXPAND
                     90: /*
                     91:  * Call the first argument for each following:
                     92:  * MACRO_FOREACH(func, a, b, c, d) expands to func(a) func(b) func(c) func(d).
                     93:  * It supports also macros as func.
                     94:  */
                     95: #define MACRO_FOREACH(call, ...) MACRO_EXPAND(MACRO_FOREACH_EXPAND(call, __VA_ARGS__))
                     96: #define MACRO_RPACK(call, terminator, ...) MACRO_EXPAND(MACRO_RPACK_EXPAND(call, terminator, __VA_ARGS__))
                     97: 
                     98: #endif