basic/utf8: modernize ascii_is_valid_n, make ascii_is_valid static inline

src/basic/utf8.c

@@ -271,27 +271,14 @@ char *utf8_escape_non_printable_full(const char *str, size_t console_width, bool
         return str_realloc(p);
 }
 
-char *ascii_is_valid(const char *str) {
-        /* Check whether the string consists of valid ASCII bytes,
-         * i.e values between 0 and 127, inclusive. */
+char* ascii_is_valid_n(const char *str, size_t len) {
+        /* Check whether the string consists of valid ASCII bytes, i.e values between 1 and 127, inclusive.
+         * Stops at len, or NUL byte if len is SIZE_MAX. */
 
         assert(str);
 
-        for (const char *p = str; *p; p++)
-                if ((unsigned char) *p >= 128)
-                        return NULL;
-
-        return (char*) str;
-}
-
-char *ascii_is_valid_n(const char *str, size_t len) {
-        /* Very similar to ascii_is_valid(), but checks exactly len
-         * bytes and rejects any NULs in that range. */
-
-        assert(str);
-
-        for (size_t i = 0; i < len; i++)
-                if ((unsigned char) str[i] >= 128 || str[i] == 0)
+        for (size_t i = 0; len != SIZE_MAX ? i < len : str[i] != '\0'; i++)
+                if ((unsigned char) str[i] >= 128 || str[i] == '\0')
                         return NULL;
 
         return (char*) str;