Add support for back tab (CSI CBT), and forward tab (CSI CHT) too.

Resolves #539.

src/terminal/terminalframebuffer.cc

@@ -214,14 +214,23 @@ void DrawState::clear_tab( int col )
   tabs[ col ] = false;
 }
 
-int DrawState::get_next_tab( void ) const
+int DrawState::get_next_tab( int count ) const
 {
-  for ( int i = cursor_col + 1; i < width; i++ ) {
-    if ( tabs[ i ] ) {
-      return i;
+  if ( count >= 0 ) {
+    for ( int i = cursor_col + 1; i < width; i++ ) {
+      if ( tabs[ i ] && --count == 0 ) {
+	return i;
+      }
     }
+    return -1;
+  } else {
+    for ( int i = cursor_col - 1; i > 0; i-- ) {
+      if ( tabs[ i ] && ++count == 0 ) {
+	return i;
+      }
+    }
+    return 0;
   }
-  return -1;
 }
 
 void DrawState::set_scrolling_region( int top, int bottom )

src/terminal/terminalframebuffer.h

@@ -286,7 +286,7 @@ namespace Terminal {
     void clear_tab( int col );
     void clear_default_tabs( void ) { default_tabs = false; }
     /* Default tabs can't be restored without resetting the draw state. */
-    int get_next_tab( void ) const;
+    int get_next_tab( int count ) const;
 
     void set_scrolling_region( int top, int bottom );
 

src/terminal/terminalfunctions.cc

@@ -201,9 +201,9 @@ static void Ctrl_NEL( Framebuffer *fb, Dispatcher *dispatch __attribute((unused)
 static Function func_Ctrl_NEL( CONTROL, "\x85", Ctrl_NEL );
 
 /* horizontal tab */
-static void Ctrl_HT( Framebuffer *fb, Dispatcher *dispatch __attribute((unused)) )
+static void HT_n( Framebuffer *fb, size_t count )
 {
-  int col = fb->ds.get_next_tab();
+  int col = fb->ds.get_next_tab( count );
   if ( col == -1 ) { /* no tabs, go to end of line */
     col = fb->ds.get_width() - 1;
   }
@@ -216,8 +216,27 @@ static void Ctrl_HT( Framebuffer *fb, Dispatcher *dispatch __attribute((unused))
   fb->ds.next_print_will_wrap = wrap_state_save;
 }
 
+static void Ctrl_HT( Framebuffer *fb, Dispatcher *dispatch __attribute((unused)) )
+{
+  HT_n( fb, 1 );
+}
 static Function func_Ctrl_HT( CONTROL, "\x09", Ctrl_HT, false );
 
+static void CSI_CxT( Framebuffer *fb, Dispatcher *dispatch )
+{
+  int param = dispatch->getparam( 0, 1 );
+  if ( dispatch->get_dispatch_chars()[ 0 ] == 'Z' ) {
+    param = -param;
+  }
+  if ( param == 0 ) {
+    return;
+  }
+  HT_n( fb, param );
+}
+
+static Function func_CSI_CHT( CSI, "I", CSI_CxT, false );
+static Function func_CSI_CBT( CSI, "Z", CSI_CxT, false );
+
 /* horizontal tab set */
 static void Ctrl_HTS( Framebuffer *fb, Dispatcher *dispatch __attribute((unused)) )
 {