json_tokener: optimize check for number characters

speedup for 32-bit: ~5%
speedup for 64-bit: ~3%

json_object.c

@@ -41,7 +41,6 @@
 // Don't define this.  It's not thread-safe.
 /* #define REFCOUNT_DEBUG 1 */
 
-const char *json_number_chars = "0123456789.+-eE";
 const char *json_hex_chars = "0123456789abcdefABCDEF";
 
 static struct json_object* json_object_new(enum json_type o_type);

json_object_private.h

@@ -51,7 +51,6 @@ struct json_object
 
 void _json_c_set_last_err(const char *err_fmt, ...);
 
-extern const char *json_number_chars;
 extern const char *json_hex_chars;
 
 #ifdef __cplusplus

json_tokener.c

@@ -73,6 +73,16 @@ static int is_hex_char(char c)
 	    || (c >= 'a' && c <= 'f');
 }
 
+static int is_number_char(char c)
+{
+	return (c >= '0' && c <= '9')
+	    || c == '.'
+	    || c == '+'
+	    || c == '-'
+	    || c == 'e'
+	    || c == 'E';
+}
+
 /* Use C99 NAN by default; if not available, nan("") should work too. */
 #ifndef NAN
 #define NAN nan("")
@@ -757,7 +767,7 @@ struct json_object* json_tokener_parse_ex(struct json_tokener *tok,
 	int case_len=0;
 	int is_exponent=0;
 	int negativesign_next_possible_location=1;
-	while(c && strchr(json_number_chars, c)) {
+	while(c && is_number_char(c)) {
 	  ++case_len;
 
 	  /* non-digit characters checks */