#include <stdio.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>

typedef struct{
	char *data;
	size_t len;
} mmapbuf;

mmapbuf *My_mmap(char *filename){
	int fd;
	char *ptr;
	size_t Mlen;
	struct stat statbuf;
	if(!filename) exit(-1);
	if((fd = open(filename, O_RDONLY)) < 0) exit(-2);
	if(fstat (fd, &statbuf) < 0) exit(-3);
	Mlen = statbuf.st_size;
	if((ptr = mmap (0, Mlen, PROT_READ, MAP_PRIVATE, fd, 0)) == MAP_FAILED)
		exit(-4);
	if(close(fd)) exit(-5);
	mmapbuf *ret = calloc(1, sizeof(mmapbuf));
	ret->data = ptr;
	ret->len = Mlen;
	return  ret;
}


int main(int argc, char **argv){
	mmapbuf *buf = My_mmap(argv[1]);
	char *afile = strdup(buf->data), *eptr = afile + buf->len;
	char *beforecom = NULL;
	while(afile < eptr){
		char *nl = strchr(afile, '\n');
		if(!nl){
			printf("%s\n", afile);
			return 0;
		}
		*nl++ = 0;
		char *commstart = strstr(afile, "/*");
		if(commstart){
			*commstart = 0;
			free(beforecom);
			beforecom = strdup(afile);
			commstart += 2;
			char *commend = NULL;
			if(*commstart) commend = strstr(commstart, "*/");
			if(commend){ // single comment
				*commend = 0;
				afile = commend + 2;
				printf("/* %s */\n", commstart);
				printf("%s%s\n", beforecom, afile);
				afile = nl + 1;
			}else{ // multiline comment
				printf("/*%s\n", commstart);
				commend = strstr(nl, "*/");
				if(!commend){
					printf("%s*/\n", nl);
					return -1;
				}
				*commend = 0;
				afile = commend + 2;
				if(*afile == '\n') ++afile;
				printf("%s*/\n", nl);
			}
		}else{
			printf("%s\n", afile);
			afile = nl;
		}
	}
}

gcc 1.c && ./a.out tw5864-reg.h|sed -e 's/ \+/ /g' -e 's/\t\+/\t/g'

79c79
< 				afile = nl;
---
> 				afile = nl + 1;

cat  tw5864-reg.h |head -50 |sed -n  "/^#define/b main;b pr;:main;/\*\/$/b endinline;g;XXX;b pr;:endinline;h;s/^[^\/]*//;p;g;s/\/\*.*$//;:pr;p"

cat  tw5864-reg.h |cat|sed -n  '
/^#define/!b pr;/\/\*/! b pr
h;s|/\*.*$||;x;s|^[^/]*||
/\*\//b both
:multi
H;n;s/^[ \t][ \t]*/\ */;H
g;s/\/\*.*//;x;s/^[^/]*//
/\*\/$/!b multi
s|/\*|/*\n *|
:both
s|**/$|*/|;p;g
:pr
s/\n//g;p'

cat  tw5864-reg.h |cat|sed -n  '
/^#define/!b pr;/\/\*/! b pr
h;s|/\*.*$||;x;s|^[^/]*||
/\*\//b in1n
:multi
H;n;s/^[ \t][ \t]*/\ */;H
g;s|/\*.*$||; x;s|^[^/]*||
/\*\/$/!b multi
s|/\*|/*\n *|
s|**/$|*/|;s|*/|\n */|;
:in1n
p;g;
:pr
s/\n//g;p'

/*
 * Video Frame mapping in DDR
 *00 CIF
 *01 D1
 *10 Reserved
 *11 Reserved
 
 */

$ cat doit.vim
:nnoremap <expr> gp '`[' . strpart(getregtype(), 0, 1) . '`]'
:let @b = '#define.*\s+\/\*'
:let @e = '\*\/'
:let @q = "/\<C-r>b/e-\<C-m>v/\<C-r>e/e\<C-m>dO\<Esc>pgp=@q"
:set nows
@q
:%s/\s\+$//g
:wq
$ vim -Nu NONE -i NONE -s doit.vim tw5864-reg.h

cat  tw5864-reg.h |cat|sed -n  '
/^#define/!b pr;/\/\*/! b pr
h;s|/\*.*$||;x;s|^[^/]*||
/\*\//b bth
H;
:multi;n;s/^[ \t][ \t]*/ * /;H;/\*\/$/!b multi
g;s|/\*.*$||;x;s|^[^/]*||;s|/\*|/*\n *|
s|**/$|*/|;s|*/|\n */|;s_\n[ \t]*\n_\n_g
:bth
p;g;
:pr
s/\n//g;p'

 sed   [OPTION]...   {script-only-if-no-other-script}   [input-
       file].

  
   Most things worth reading carefully are likely to present some difficulties to the reader on a first reading. These difficulties tend to slow us up. But we should never allow them to stop us in our tracks.
   Readers who bog down completely because they cannot fully understand some statement or reference in the course of their reading fail to  recognize that no  one can be expected to achieve complete  understanding of a significant work on the first go at it.
   A first reading is bound to be a relatively superficial one, as compared  with the reading in greater and greater depth that can be done when one rereads the same work later

#!/usr/bin/perl -n

if (s{^#\s*define .*?\K(\s*)(/\*.*)}{}) {
  my ($define, $margin, $comment) = ($_, $1, $2);
  $margin = $-[1] + length($margin) + ($margin =~ tr/\t/\t/ * 7);
  if ($comment =~ m{\*/}) {
    print $comment, "\n";
  } else {
    $comment =~ s{/\*\K}{\n *};
    print $comment;
    while (<>) {
       s/\G\t/' ' x 8/ge;
       s/^ {$margin}//;
       print ' *' unless s{^\s*\*/}{ */};
       print;
       last if m{\*/};
    };
  };
  print $define;
  next;
};

print;