--- a/libcoding/Makefile	Sat Aug 05 05:45:15 2023 +0000
+++ b/libcoding/Makefile	Sat Aug 05 06:32:37 2023 +0000
@@ -1,7 +1,7 @@
 CC=	gcc
 CFLAGS=	-O2
-OBJS=	gsm7_encode.o gsm7_encode_table.o gsm7_pack.o hexout.o number_encode.o \
-	timestamp.o ucs2_bigend.o utf8_decode.o utf8_decode2.o
+OBJS=	gsm7_encode.o gsm7_encode_table.o gsm7_pack.o hexdigits.o hexout.o \
+	number_encode.o timestamp.o ucs2_bigend.o utf8_decode.o utf8_decode2.o
 LIB=	libcoding.a
 
 all:	${LIB}

--- /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');
+}