libbb: make index_in_substrings return -1 on ambiguous matches

function                                             old     new   delta
index_in_substrings                                   67      93     +26

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

libbb/compare_string_array.c

@@ -53,19 +53,24 @@ int FAST_FUNC index_in_substr_array(const char *const string_array[], const char
 
 int FAST_FUNC index_in_substrings(const char *strings, const char *key)
 {
-	int len = strlen(key);
+	int matched_idx = -1;
+	const int len = strlen(key);
 
 	if (len) {
 		int idx = 0;
 		while (*strings) {
 			if (strncmp(strings, key, len) == 0) {
-				return idx;
+				if (strings[len] == '\0')
+					return idx; /* exact match */
+				if (matched_idx >= 0)
+					return -1; /* ambiguous match */
+				matched_idx = idx;
 			}
 			strings += strlen(strings) + 1; /* skip NUL */
 			idx++;
 		}
 	}
-	return -1;
+	return matched_idx;
 }
 
 const char* FAST_FUNC nth_string(const char *strings, int n)
@@ -76,3 +81,15 @@ const char* FAST_FUNC nth_string(const char *strings, int n)
 	}
 	return strings;
 }
+
+#ifdef UNUSED_SO_FAR /* only brctl.c needs it yet */
+/* Returns 0 for no, 1 for yes or a negative value on error.  */
+smallint FAST_FUNC yesno(const char *str)
+{
+	static const char no_yes[] ALIGN1 =
+		"0\0" "off\0" "no\0"
+		"1\0" "on\0" "yes\0";
+	int ret = index_in_substrings(no_yes, str);
+	return ret / 3;
+}
+#endif

networking/brctl.c

@@ -220,10 +220,10 @@ int brctl_main(int argc UNUSED_PARAM, char **argv)
 		}
 #if ENABLE_FEATURE_BRCTL_FANCY
 		if (key == ARG_stp) { /* stp */
-			static const char stp_opts[] ALIGN1 =
+			static const char no_yes[] ALIGN1 =
 				"0\0" "off\0" "n\0" "no\0"   /* 0 .. 3 */
 				"1\0" "on\0"  "y\0" "yes\0"; /* 4 .. 7 */
-			int onoff = index_in_strings(stp_opts, *argv);
+			int onoff = index_in_strings(no_yes, *argv);
 			if (onoff < 0)
 				bb_error_msg_and_die(bb_msg_invalid_arg, *argv, applet_name);
 			onoff = (unsigned)onoff / 4;

networking/udhcp/common.c

@@ -435,8 +435,8 @@ int FAST_FUNC udhcp_str2optset(const char *const_str, void *arg)
 			}
 			break;
 //		case OPTION_BOOLEAN: {
-//			static const char noyes[] ALIGN1 = "no\0yes\0";
+//			static const char no_yes[] ALIGN1 = "no\0yes\0";
-//			buffer[0] = retval = index_in_strings(noyes, val);
+//			buffer[0] = retval = index_in_strings(no_yes, val);
 //			retval++; /* 0 - bad; 1: "no" 2: "yes" */
 //			break;
 //		}