Hi Emacs developers,

I've extensively modified hideif.el as attached and would like to
contribute it back to Emacs. I've also posted it on EmacsWiki earlier
http://www.emacswiki.org/emacs/HideIfDef. Here is the original posting:

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An extensively rewritten version is uploaded. Here I list some of the
enhancements:
* Automatically find and add #define macros when hiding
* Complete C expression with operator precedence implemented
* Hex/octal/decimal number supported
* Bit shift operation supported
* Stringification / string concatenation / token concatenation supported
* Argumented macro expansion supported, even for complicated and rarely
used token replacement syntax.

#define TESTVAL1 0x123
#define TESTVAL2 291 // 0x123

#define CONCAT(x,y) x ## y
#define CONCAT2(x,y) CONCAT(x,y)

#if CONCAT( TESTVAL1=,=TESTVAL2 )
#error correct
#else
#error wrong
#endif

#if CONCAT( TESTVAL1!,=TESTVAL2 )
#error wrong
#else
#error correct
#endif

after hiding, it will become

#define TESTVAL1 0x123
#define TESTVAL2 291 // 0x123

#define CONCAT(x,y) x ## y
#define CONCAT2(x,y) CONCAT(x,y)

#if CONCAT( TESTVAL1=,=TESTVAL2 )
#error correct
#else...
#endif

#if CONCAT( TESTVAL1!,=TESTVAL2 )...
#else
#error correct
#endif

* GNU C compatibility, i.e. "..." in macro argument supported.
Ex. #define macro(arg1, arg2...) arg1 + arg2
* hide/unhide a region
* Evaluate a macro, just mark the region you want to evalute and press "C-c
@ e"
* When hiding #if..#endif themselves, consecutive "..." "..." will be
merged as a single "..."

Tips:
* All C files share the same macro database (i.e. hide-ifdef-env).
* Goto your "config.h" file and hide it, it will extract all #defines.
* Goto each of your .h file in the order that C compiler compiles your C
file, hide each .h file one by one. (TODO: project support, auto search for
.h files)
* To save your current macro database, you need to deploy "session" package
and add the following into your init.el file:
(unless (assoc 'hide-ifdef-env session-globals-include)
  (push '(hide-ifdef-env 100000 t) session-globals-include))
* To exclude some patterns (to reduce the size of macro database), for
example, if you want to exclude all macros started with "DOC_", put the
following into your init.el:
(setf hide-ifdef-exclude-define-regexp-pattern "DOC_.*")

Compatibility note:

The original "semantic" hack no longer work.
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Thanks for all those nice Emacs experiences!

-- 
Best regards,
Luke Lee