libfdt: Factor out string search function

This patch pulls out the logic for finding a string in the string table
into _fdt_find_string(), from fdt_sw.c's find_add_string().  This function
will be useful for random-access read-write functions.  In the process
clean up the search logic a little.

fdt.c

@@ -92,6 +92,18 @@ uint32_t _fdt_next_tag(const struct fdt_header *fdt, int offset, int *nextoffset
 	return tag;
 }
 
+const char *_fdt_find_string(const char *strtab, int tabsize, const char *s)
+{
+	int len = strlen(s) + 1;
+	const char *last = strtab + tabsize - len;
+	const char *p;
+
+	for (p = strtab; p <= last; p++)
+		if (memeq(p, s, len))
+			return p;
+	return NULL;
+}
+
 struct fdt_header *fdt_move(const struct fdt_header *fdt, void *buf, int bufsize)
 {
 	int err = _fdt_check_header(fdt);

fdt_sw.c

@@ -131,19 +131,14 @@ int fdt_end_node(struct fdt_header *fdt)
 static int find_add_string(struct fdt_header *fdt, const char *s)
 {
 	char *strtab = (char *)fdt + fdt_totalsize(fdt);
+	const char *p;
 	int strtabsize = fdt_size_dt_strings(fdt);
 	int len = strlen(s) + 1;
 	int struct_top, offset;
 
-	/* We treat string offsets as negative from the end of our buffer */
-	/* then fix them up in fdt_finish() */
-	offset = -strtabsize;
-	while ((offset < 0) && (memcmp(strtab + offset, s, len) != 0))
-		offset++;
-
-	if (offset < 0)
-		/* Found it */
-		return offset;
+	p = _fdt_find_string(strtab - strtabsize, strtabsize, s);
+	if (p)
+		return p - strtab;
 
 	/* Add it */
 	offset = -strtabsize - len;

libfdt_internal.h

@@ -30,7 +30,7 @@ int _fdt_check_header(const struct fdt_header *fdt);
 uint32_t _fdt_next_tag(const struct fdt_header *fdt, int startoffset, int *nextoffset);
 struct fdt_property *_fdt_getprop(const struct fdt_header *fdt, int nodeoffset,
 				  const char *name, int *lenp);
-
+const char *_fdt_find_string(const char *strtab, int tabsize, const char *s);
 
 #define OFFSET_ERROR(code)	-(code)
 #define PTR_ERROR(code)		(void *)(-(code))