--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libcoding/gsm7_decode.c	Thu Jun 13 02:29:29 2024 +0000
@@ -0,0 +1,77 @@
+/*
+ * This library module implements the decoding of GSM7-encoded data
+ * into ASCII, ISO 8859-1 or UTF-8.
+ */
+
+#include <sys/types.h>
+#include <stdio.h>
+
+extern u_short gsm7_decode_table[128];
+extern u_short gsm7ext_decode_table[128];
+
+gsm7_to_ascii_or_ext(inbuf, inlen, outbuf, outlenp, ascii_ext, newline_ok)
+	u_char *inbuf, *outbuf;
+	unsigned inlen, *outlenp;
+{
+	u_char *inp, *endp, *outp;
+	unsigned gsm, uni;
+	int is_ext;
+
+	inp = inbuf;
+	endp = inbuf + inlen;
+	outp = outbuf;
+	while (inp < endp) {
+		gsm = *inp++;
+		if (gsm == 0x1B && inp < endp && *inp != 0x1B && *inp != '\n'
+		    && *inp != '\r') {
+			gsm = *inp++;
+			uni = gsm7ext_decode_table[gsm];
+			if (uni == '\\') {
+				*outp++ = '\\';
+				*outp++ = '\\';
+				continue;
+			}
+			if (uni == 0x20AC && ascii_ext < 2) {
+				*outp++ = '\\';
+				*outp++ = 'E';
+				continue;
+			}
+			is_ext = 1;
+		} else {
+			switch (gsm) {
+			case 0x1B:
+				*outp++ = '\\';
+				*outp++ = 'e';
+				continue;
+			case '\n':
+				if (newline_ok)
+					*outp++ = '\n';
+				else {
+					*outp++ = '\\';
+					*outp++ = 'n';
+				}
+				continue;
+			case '\r':
+				*outp++ = '\\';
+				*outp++ = 'r';
+				continue;
+			}
+			uni = gsm7_decode_table[gsm];
+			is_ext = 0;
+		}
+		if (!uni || !is_decoded_char_ok(uni, ascii_ext)) {
+			if (is_ext) {
+				*outp++ = '\\';
+				*outp++ = 'e';
+			}
+			sprintf(outp, "\\%02X", gsm);
+			outp += 3;
+		} else if (ascii_ext == 2)
+			outp += emit_utf8_char(uni, outp);
+		else
+			*outp++ = uni;
+	}
+	*outp = '\0';
+	if (outlenp)
+		*outlenp = outp - outbuf;
+}