Macro: Added a bunch of dirty C preprocessor tricks

Included are Makefile implicit rules to show the preprocessed source.
When debugging something around this, it may be handy.

Makefile.in

@@ -95,7 +95,7 @@ clean = $(eval $(call clean_in,$(1)))
 include $(addsuffix /Makefile,$(addprefix $(srcdir)/,$(dirs)))
 
 # Generic rules
-
+# Object file rules
 $(objdir)/%.o: $(srcdir)/%.c $(objdir)/.dir-stamp $(objdir)/sysdep/paths.h
 	$(E)echo CC -o $@ -c $<
 	$(Q)$(CC) $(CFLAGS) -MMD -MP -o $@ -c $<
@@ -104,7 +104,16 @@ $(objdir)/%.o: $(objdir)/%.c $(objdir)/.dir-stamp $(objdir)/sysdep/paths.h
 	$(E)echo CC -o $@ -c $<
 	$(Q)$(CC) $(CFLAGS) -MMD -MP -o $@ -c $<
 
+# Debug: Preprocessed source rules
+$(objdir)/%.E: $(srcdir)/%.c $(objdir)/.dir-stamp $(objdir)/sysdep/paths.h
+	$(E)echo CC -o $@ -E $<
+	$(Q)$(CC) $(CFLAGS) -MMD -MP -o $@ -E $<
 
+$(objdir)/%.E: $(objdir)/%.c $(objdir)/.dir-stamp $(objdir)/sysdep/paths.h
+	$(E)echo CC -o $@ -E $<
+	$(Q)$(CC) $(CFLAGS) -MMD -MP -o $@ -E $<
+
+# Debug: Assembler object rules
 $(objdir)/%.S: $(srcdir)/%.c $(objdir)/.dir-stamp $(objdir)/sysdep/paths.h
 	$(E)echo CC -o $@ -S $<
 	$(Q)$(CC) $(CFLAGS) -MMD -MP -o $@ -S $<

lib/macro.h

@@ -0,0 +1,98 @@
+/* 
+ *	BIRD Macro Tricks
+ *
+ *	(c) 2018 Jan Maria Matejka <mq@jmq.cz>
+ *
+ *	Can be freely distributed and used under the terms of the GNU GPL.
+ *
+ *	Contains useful but dirty macro tricks:
+ *		MACRO_CONCAT(a, b)	-> concatenates a##b
+ *		MACRO_BOOL(x)		-> convert 0 to 0, anything else to 1
+ *		MACRO_IFELSE(b)(true-branch)(false-branch)
+ *					-> b shall be 0 or 1; expands to the appropriate branch
+ *		MACRO_ISEMPTY(...)	-> 1 for empty argument list, 0 otherwise
+ *		MACRO_FOREACH(func, ...)
+ *					-> calling FOREACH(func, a, b, c, d) expands to
+ *						func(a) func(b) func(c) func(d)
+ *		MACRO_RPACK(func, terminator, ...)
+ *					-> packs the list into recursive calls:
+ *						func(func(func(func(terminator, a), b), c), d)
+ */
+
+#ifndef _BIRD_MACRO_H_
+#define _BIRD_MACRO_H_
+
+/* What to do with args */
+#define MACRO_DROP(...)
+#define MACRO_UNPAREN(...) __VA_ARGS__
+#define MACRO_SEP(a, b, sep)  a sep b
+
+/* Aliases for some special chars */
+#define MACRO_COMMA ,
+#define MACRO_LPAREN (
+#define MACRO_RPAREN )
+#define MACRO_LPAREN_() (
+#define MACRO_RPAREN_() )
+
+/* Multiple expansion trick */
+#define MACRO_EXPAND0(...) __VA_ARGS__
+#define MACRO_EXPAND1(...) MACRO_EXPAND0(MACRO_EXPAND0(__VA_ARGS__))
+#define MACRO_EXPAND2(...) MACRO_EXPAND1(MACRO_EXPAND1(__VA_ARGS__))
+#define MACRO_EXPAND3(...) MACRO_EXPAND2(MACRO_EXPAND2(__VA_ARGS__))
+#define MACRO_EXPAND(...) MACRO_EXPAND3(MACRO_EXPAND3(__VA_ARGS__))
+
+/* Deferring expansion in the expansion trick */
+#define MACRO_EMPTY()
+#define MACRO_DEFER(t) t MACRO_EMPTY()
+#define MACRO_DEFER2(t) t MACRO_EMPTY MACRO_EMPTY()()
+#define MACRO_DEFER3(t) t MACRO_EMPTY MACRO_EMPTY MACRO_EMPTY()()()
+
+/* Token concatenation */
+#define MACRO_CONCAT(prefix, ...) prefix##__VA_ARGS__
+#define MACRO_CONCAT_AFTER(...) MACRO_CONCAT(__VA_ARGS__)
+
+/* Get first or second argument only */
+#define MACRO_FIRST(a, ...) a
+#define MACRO_SECOND(a, b, ...) b
+#define MACRO_SECOND_OR_ZERO(...) MACRO_SECOND(__VA_ARGS__, 0,)
+
+/* Macro Boolean auxiliary macros */
+#define MACRO_BOOL_CHECK_0 ~, 1
+#define MACRO_BOOL_NEG(x) MACRO_SECOND_OR_ZERO(MACRO_CONCAT(MACRO_BOOL_CHECK_, x))
+
+#define MACRO_BOOL_NOT_0  1
+#define MACRO_BOOL_NOT_1  0
+
+/* Macro Boolean negation */
+#define MACRO_NOT(x) MACRO_CONCAT(MACRO_BOOL_NOT_, x)
+
+/* Convert anything to bool (anything -> 1, 0 -> 0) */
+#define MACRO_BOOL(x) MACRO_NOT(MACRO_BOOL_NEG(x))
+
+/*
+ * Macro If/Else condition
+ * Usage: MACRO_IFELSE(condition)(true-branch)(false-branch)
+ * Expands to true-branch if condition is true, otherwise to false-branch.
+ */
+#define MACRO_IFELSE(b) MACRO_CONCAT(MACRO_IFELSE_, b)
+#define MACRO_IFELSE_0(...) MACRO_UNPAREN
+#define MACRO_IFELSE_1(...) __VA_ARGS__ MACRO_DROP
+
+/* Auxiliary macros for MACRO_FOREACH */
+#define MACRO_ISLAST(...) MACRO_BOOL_NEG(MACRO_FIRST(MACRO_ISLAST_CHECK __VA_ARGS__)())
+#define MACRO_ISLAST_CHECK() 0
+
+#define MACRO_FOREACH_EXPAND(call, a, ...) MACRO_IFELSE(MACRO_ISLAST(__VA_ARGS__))(call(a))(call(a) MACRO_DEFER2(MACRO_FOREACH_PAREN)()(call, __VA_ARGS__))
+#define MACRO_FOREACH_PAREN() MACRO_FOREACH_EXPAND
+
+#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))
+#define MACRO_RPACK_PAREN() MACRO_RPACK_EXPAND
+/*
+ * Call the first argument for each following:
+ * MACRO_FOREACH(func, a, b, c, d) expands to func(a) func(b) func(c) func(d).
+ * It supports also macros as func.
+ */
+#define MACRO_FOREACH(call, ...) MACRO_EXPAND(MACRO_FOREACH_EXPAND(call, __VA_ARGS__))
+#define MACRO_RPACK(call, terminator, ...) MACRO_EXPAND(MACRO_RPACK_EXPAND(call, terminator, __VA_ARGS__))
+
+#endif