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	cleanname.c - 9base - revived minimalist port of Plan 9 userland to Unix
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	cleanname.c (1199B)
	---
	1 #include <u.h>
	2 #include <libc.h>
	3
	4 /*
	5 * In place, rewrite name to compress multiple /, eliminate ., and proce…
	6 */
	7 #define SEP(x) ((x)=='/' \|\| (x) == 0)
	8 char*
	9 cleanname(char *name)
	10 {
	11 char p, q, *dotdot;
	12 int rooted;
	13
	14 rooted = name[0] == '/';
	15
	16 /*
	17 * invariants:
	18 * p points at beginning of path element we're considerin…
	19 * q points just past the last path element we wrote (no …
	20 * dotdot points just past the point where .. cannot back…
	21 * any further (no slash).
	22 */
	23 p = q = dotdot = name+rooted;
	24 while(*p) {
	25 if(p[0] == '/') /* null element */
	26 p++;
	27 else if(p[0] == '.' && SEP(p[1]))
	28 p += 1; /* don't count the separator in c…
	29 else if(p[0] == '.' && p[1] == '.' && SEP(p[2])) {
	30 p += 2;
	31 if(q > dotdot) { /* can backtrack */
	32 while(--q > dotdot && *q != '/')
	33 ;
	34 } else if(!rooted) { /* /.. is / but ./..…
	35 if(q != name)
	36 *q++ = '/';
	37 *q++ = '.';
	38 *q++ = '.';
	39 dotdot = q;
	40 }
	41 } else { /* real path element */
	42 if(q != name+rooted)
	43 *q++ = '/';
	44 while((q = p) != '/' && *q != 0)
	45 p++, q++;
	46 }
	47 }
	48 if(q == name) /* empty string is really ``.'' */
	49 *q++ = '.';
	50 *q = '\0';
	51 return name;
	52 }