+/* ISDIGIT differs from isdigit, as follows:
+ - Its arg may be any int or unsigned int; it need not be an unsigned char.
+ - It's guaranteed to evaluate its argument exactly once.
+ - It's typically faster.
+ Posix 1003.2-1992 section 2.5.2.1 page 50 lines 1556-1558 says that
+ only '0' through '9' are digits. Prefer ISDIGIT to isdigit unless
+ it's important to use the locale's definition of `digit' even when the
+ host does not conform to Posix. */
+#define ISDIGIT(c) ((unsigned) (c) - '0' <= 9)
+
+#ifndef strdup