--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libcommon/gsm7_unpack.c	Sat Feb 13 04:31:02 2021 +0000
@@ -0,0 +1,22 @@
+/*
+ * This library module implements unpacking of GSM 7-bit data
+ * from packed octets.
+ */
+
+#include <sys/types.h>
+
+static u_char shift[8] = {0, 7, 6, 5, 4, 3, 2, 1};
+
+gsm7_unpack(inbuf, outbuf, nseptets)
+	u_char *inbuf, *outbuf;
+	unsigned nseptets;
+{
+	u_char *inp = inbuf, *outp = outbuf;
+	unsigned n;
+
+	for (n = 0; n < nseptets; n++) {
+		*outp++ = (((inp[1] << 8) | inp[0]) >> shift[n&7]) & 0x7F;
+		if (n & 7)
+			inp++;
+	}
+}