Read saveset name from the right place

Support DUMPER format 6, which has saveset name at different offset. Also check dumper tape format and reject too old or invalid format codes.

dumper.h

@@ -80,9 +80,13 @@ char *rectypes[] = {
 #define BtoffWord       0
 #define BtlenWord       36
 
+#define WdoffSSstart	6	/* Start of saveset data */
+#define WdoffSSFmt	   6	/* Format of tape */
+#define WdoffSSPtr	   7	/* Pointer to saveset name (or 3 or 020 depending on format) */
 #define WdoffSSDate        8            /* Saveset date offset (type 1, 6) */
 #define WdoffSSName        9            /* Saveset name offset (type 1, 6) */
 #define WdoffFLName        6            /* Filename offset (type 2) */
+#define WdoffSSMsg	  (020+WdoffSSstart) /* Saveset name (unless SSPtr set) */
 #define WdoffFDB         134            /* FDB offset (type 2) */
 
 #define WdoffFDB_CTL	01+WdoffFDB	/* Control word .FBCTL */

read20.c

@@ -519,13 +519,32 @@ void doSaveset (char *block, int contflag)
 {
 	static char name[102];
 	static char ss[2];
+	long ssfmt, ssptr;
 	long t;
 
 	if (debug > 10) printf("\nSaveset header:");
 	tapeno = getfield(block, WdoffTapeNum, BtoffTapeNum, BtlenTapeNum);
 	ssno = getfield(block, WdoffSaveSetNum, BtoffSaveSetNum,
 	    BtlenSaveSetNum);
-	getstring(block, name, WdoffSSName, sizeof(name));
+	ssfmt = getfield(block, WdoffSSFmt, BtoffWord, BtlenWord); /* Get format */
+	ssptr = getfield(block, WdoffSSPtr, BtoffWord, BtlenWord); /* Get pointer */
+	// Check tape format! Otherwise breaks e.g. on Install tapes (which aren't in dumper format).
+	if ((ssfmt < 4) || (ssfmt > 6)) {
+	  // Formats older than 4 not supported, and 6 was the highest (TOPS-20 v6-7).
+	  // If you want to support older fmts, write the code. :-)
+	  fprintf (stderr, "Bad dumper tape format %012lo\n", ssfmt);
+	  exit(1);
+	}
+
+	if (verbose) {
+	  printf("Saveset format %ld, name pointer %ld; tape %ld, saveset %ld\n", ssfmt, ssptr, tapeno, ssno);
+	}
+	if (ssptr == 0) {
+	  /* If there is no pointer, use default offset: for format 5-6 (T20 v6-7), SS.MSG, otherwise (T20 v4-5) BFMSG */
+	  getstring(block, name, ssfmt > 4 ? WdoffSSMsg : WdoffSSName, sizeof(name));
+	} else {
+	  getstring(block, name, ssptr+WdoffSSstart, sizeof(name));
+	}
 	ss[0] = pendstring();		/* superfluous */
 	(void) strcat(name, ss);