cord_pos.h

gcc-you can use this code to learn something about gcc, and inquire further into linux,

/* 
 * Copyright (c) 1993-1994 by Xerox Corporation.  All rights reserved.
 *
 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
 * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
 *
 * Permission is hereby granted to use or copy this program
 * for any purpose,  provided the above notices are retained on all copies.
 * Permission to modify the code and to distribute modified code is granted,
 * provided the above notices are retained, and a notice that the code was
 * modified is included with the above copyright notice.
 */
/* Boehm, May 19, 1994 2:23 pm PDT */
# ifndef CORD_POSITION_H

/* The representation of CORD_position.  This is private to the	*/
/* implementation, but the size is known to clients.  Also	*/
/* the implementation of some exported macros relies on it.	*/
/* Don't use anything defined here and not in cord.h.		*/

# define MAX_DEPTH 48
	/* The maximum depth of a balanced cord + 1.		*/
	/* We don't let cords get deeper than MAX_DEPTH.	*/

struct CORD_pe {
    CORD pe_cord;
    size_t pe_start_pos;
};

/* A structure describing an entry on the path from the root 	*/
/* to current position.						*/
typedef struct CORD_Pos {
    size_t cur_pos;
    int path_len;
#	define CORD_POS_INVALID (0x55555555)
		/* path_len == INVALID <==> position invalid */
    const char *cur_leaf;	/* Current leaf, if it is a string.	*/
    				/* If the current leaf is a function,	*/
    				/* then this may point to function_buf	*/
    				/* containing the next few characters.	*/
    				/* Always points to a valid string	*/
    				/* containing the current character 	*/
    				/* unless cur_end is 0.			*/
    size_t cur_start;	/* Start position of cur_leaf	*/
    size_t cur_end;	/* Ending position of cur_leaf	*/
    			/* 0 if cur_leaf is invalid.	*/
    struct CORD_pe path[MAX_DEPTH + 1];
    	/* path[path_len] is the leaf corresponding to cur_pos	*/
    	/* path[0].pe_cord is the cord we point to.		*/
#   define FUNCTION_BUF_SZ 8
    char function_buf[FUNCTION_BUF_SZ];	/* Space for next few chars	*/
    					/* from function node.		*/
} CORD_pos[1];

/* Extract the cord from a position:	*/
CORD CORD_pos_to_cord(CORD_pos p);
	
/* Extract the current index from a position:	*/
size_t CORD_pos_to_index(CORD_pos p);
	
/* Fetch the character located at the given position:	*/
char CORD_pos_fetch(CORD_pos p);
	
/* Initialize the position to refer to the give cord and index.	*/
/* Note that this is the most expensive function on positions:	*/
void CORD_set_pos(CORD_pos p, CORD x, size_t i);
	
/* Advance the position to the next character.	*/
/* P must be initialized and valid.		*/
/* Invalidates p if past end:			*/
void CORD_next(CORD_pos p);

/* Move the position to the preceding character.	*/
/* P must be initialized and valid.			*/
/* Invalidates p if past beginning:			*/
void CORD_prev(CORD_pos p);
	
/* Is the position valid, i.e. inside the cord?		*/
int CORD_pos_valid(CORD_pos p);

char CORD__pos_fetch(CORD_pos);
void CORD__next(CORD_pos);
void CORD__prev(CORD_pos);

#define CORD_pos_fetch(p)	\
    (((p)[0].cur_end != 0)? \
     	(p)[0].cur_leaf[(p)[0].cur_pos - (p)[0].cur_start] \
     	: CORD__pos_fetch(p))

#define CORD_next(p)	\
    (((p)[0].cur_pos + 1 < (p)[0].cur_end)? \
    	(p)[0].cur_pos++ \
    	: (CORD__next(p), 0))

#define CORD_prev(p)	\
    (((p)[0].cur_end != 0 && (p)[0].cur_pos > (p)[0].cur_start)? \
    	(p)[0].cur_pos-- \
    	: (CORD__prev(p), 0))

#define CORD_pos_to_index(p) ((p)[0].cur_pos)

#define CORD_pos_to_cord(p) ((p)[0].path[0].pe_cord)

#define CORD_pos_valid(p) ((p)[0].path_len != CORD_POS_INVALID)

/* Some grubby stuff for performance-critical friends:	*/
#define CORD_pos_chars_left(p) ((long)((p)[0].cur_end) - (long)((p)[0].cur_pos))
	/* Number of characters in cache.  <= 0 ==> none	*/

#define CORD_pos_advance(p,n) ((p)[0].cur_pos += (n) - 1, CORD_next(p))
	/* Advance position by n characters	*/
	/* 0 < n < CORD_pos_chars_left(p)	*/

#define CORD_pos_cur_char_addr(p) \
	(p)[0].cur_leaf + ((p)[0].cur_pos - (p)[0].cur_start)
	/* address of current character in cache.	*/

#endif