From 218e060a55184be55ef87795613fb397e57f195d Mon Sep 17 00:00:00 2001
From: Warren Toomey <wkt@tuhs.org>
Date: Fri, 4 Mar 2016 13:39:38 +1000
Subject: [PATCH] I've added the seek() system call to a7out. I've also added
 some heuristic code to detect if file output is "binary" or ASCII and to
 write the file correctly. Mind you, the heuristic can fail :-( The original
 cp can now copy ASCII and binary files.

---
 tools/a7out | 64 ++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 46 insertions(+), 18 deletions(-)

diff --git a/tools/a7out b/tools/a7out
index 57e91e4..84dc7b2 100755
--- a/tools/a7out
+++ b/tools/a7out
@@ -552,37 +552,32 @@ sub cal {
     # Syscalls that we can simulate
     my %Syscallist = (
 
-        # 1: save
+        # 1:       save
         2 => \&sys_getuid,
         3 => \&sys_open,
         4 => \&sys_read,
         5 => \&sys_write,
         6 => \&sys_creat,
-
-        # 7 seek
-        # 8 tell
+        7 => \&sys_seek,
+        # 8        tell
         9 => \&sys_close,
-
-        # 10 link
+        # 10        link
         11 => \&sys_unlink,
         12 => \&sys_setuid,
-
-        # 13 rename
+        # 13        rename
         14 => \&sys_exit,
         15 => \&sys_time,
         16 => \&sys_intrp,
         17 => \&sys_chdir,
         18 => \&sys_chmod,
         19 => \&sys_chown,
-
-        # 20 badcal
-        # 21 syslog
-        # 22 badcal
-        # 23 capt
-        # 24 rele
+        # 20        badcal
+        # 21        syslog
+        # 22        badcal
+        # 23        capt
+        # 24        rele
         25 => \&sys_status,
-
-        # 26 badcal
+        # 26    badcal
         27 => \&sys_smes,
         28 => \&sys_rmes,
         29 => \&sys_fork,
@@ -700,6 +695,9 @@ sub opensomething {
     if ( !-d $filename ) {
         open( $FH, $readorwrite, $filename ) || return (undef);
 
+	# Opened for writing, so for now this is not binary
+	return ( $FH, 0) if ($readorwrite eq ">");
+
         # Determine if the file is pure ASCII or contains 18-bit
         # words encoded in 24-bit groups. We test the msb of the
         # first character in the file. If it's on then it's a
@@ -749,6 +747,7 @@ sub opensomething {
     close($FH);
     open( $FH, "<", $tempfile ) || return (undef);
     binmode($FH);
+    #exit(0);
     unlink($tempfile);
     return ( $FH, 1 );
 }
@@ -907,11 +906,19 @@ sub sys_write {
         return;
     }
 
-    # Write each word out
+    # Write each word out either in binary or in ASCII
     my $FH = $FD[$fd];
     foreach my $addr ( $start .. $end ) {
+	# First see if any "non-ASCII" bits are set in the word.
+	# If so, then this is a binary file
+	my $word= $Mem[$addr];
+	$ISBINARY[$fd]=1 if ($word & 0600600);
 
-        print( $FH word2ascii( $Mem[$addr] ) );
+	if ($ISBINARY[$fd]) {
+	    print( $FH word2three($word) );
+	} else {
+            print( $FH word2ascii($word) );
+	}
     }
 
     # No error
@@ -1094,6 +1101,27 @@ sub sys_status {
     return;
 }
 
+# Seek syscall
+sub sys_seek {
+    # Seek takes three arguments: AC is the fd, PC+1 is a signed count
+    # and PC+1 is how to seek: 0=from start, 1=from curptr, 2=from end
+    # of file. Return AC=0 if OK, -1 on error.
+    my $fd= $AC;
+    my $FH= $FD[$fd];
+    my $offset= $Mem[ $PC + 1 ];
+    # XXX For now, we always do SEEK_SET.
+
+    # If it's a binary file, we have to seek 3 bytes for every word,
+    # but for an ASCII file that's 2 bytes per word.
+    $offset *= ($ISBINARY[$fd]) ? 3 : 2;
+    my $result= seek($FH, $offset, SEEK_SET);
+
+    # Set the AC result
+    $AC= ($result)? 0: MAXINT;
+    $PC += 3;
+    return;
+}
+
 # Convert an 18-bit word into a scalar which has three sixbit
 # values in three bytes. Set the msb in the first byte
 sub word2three {