--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libcoding/hexdigits.c	Sat Aug 05 06:32:37 2023 +0000
@@ -0,0 +1,23 @@
+/*
+ * This module contains elementary functions for working with hex digits.
+ */
+
+decode_hex_digit(c)
+{
+	if (c >= '0' && c <= '9')
+		return(c - '0');
+	if (c >= 'A' && c <= 'F')
+		return(c - 'A' + 10);
+	if (c >= 'a' && c <= 'f')
+		return(c - 'a' + 10);
+	return(-1);
+}
+
+encode_hex_digit(d)
+	unsigned d;
+{
+	if (d <= 9)
+		return(d + '0');
+	else
+		return(d - 10 + 'A');
+}