gdb: Add 'tui reg prev' command.

There is already a 'tui reg next' command, this adds a symmetric 'tui
reg prev' command.

gdb/ChangeLog:

	* tui/tui-regs.c (tui_reg_prev_command): New function.
	(_initialize_tui_regs): Add 'prev' command for 'tui reg'.
	* reggroups.c (reggroup_prev): New function.
	* reggroups.h (reggroup_prev): Add declaration.  Update comment.

gdb/doc/ChangeLog:

	* gdb.texinfo (TUI Commands): Add 'tui reg prev' details.

1 files changed, 26 insertions, 0 deletions

diff --git a/gdb/tui/tui-regs.c b/gdb/tui/tui-regs.c
index 8d4c0f8..7cf386d 100644
--- a/gdb/tui/tui-regs.c
+++ b/gdb/tui/tui-regs.c
@@ -575,6 +575,29 @@ tui_reg_next_command (char *arg, int from_tty)
     }
 }
 
+/* Implementation of the "tui reg prev" command.  Cycle the register group
+   displayed in the tui REG window, moving backwards through the list of
+   available register groups.  */
+
+static void
+tui_reg_prev_command (char *arg, int from_tty)
+{
+  struct gdbarch *gdbarch = get_current_arch ();
+
+  if (TUI_DATA_WIN != NULL)
+    {
+      struct reggroup *group
+        = TUI_DATA_WIN->detail.data_display_info.current_group;
+
+      group = reggroup_prev (gdbarch, group);
+      if (group == NULL)
+	group = reggroup_prev (gdbarch, NULL);
+
+      if (group != NULL)
+	tui_show_registers (group);
+    }
+}
+
 static void
 tui_reg_float_command (char *arg, int from_tty)
 {
@@ -630,6 +653,9 @@ _initialize_tui_regs (void)
   add_cmd ("next", class_tui, tui_reg_next_command,
            _("Display next register group."),
            &tuireglist);
+  add_cmd ("prev", class_tui, tui_reg_prev_command,
+           _("Display previous register group."),
+           &tuireglist);
 }