Add command to reverse marked images

README.md

@@ -108,6 +108,7 @@ of small previews is displayed, making it easy to choose an image to open.
     D            Remove image from file list and go to next image
 
     m            Mark/unmark current image
+    M            Reverse marked images
     N            Go [count] marked images forward
     P            Go [count] marked images backward
 

commands.c

@@ -251,6 +251,18 @@ bool it_toggle_image_mark(arg_t a)
 	return true;
 }
 
+bool it_reverse_marks(arg_t a)
+{
+	int i, cnt = mode == MODE_IMAGE ? filecnt : tns.cnt;
+
+        for (i = 0; i < cnt; i++) {
+		files[i].marked = !files[i].marked;
+		markcnt += files[i].marked ? 1 : -1;
+        }
+
+	return true;
+}
+
 bool it_navigate_marked(arg_t a)
 {
 	long n = (long) a;

commands.h

@@ -55,6 +55,7 @@ bool it_n_or_last(arg_t);
 bool i_navigate_frame(arg_t);
 bool i_toggle_animation(arg_t);
 bool it_toggle_image_mark(arg_t);
+bool it_reverse_marks(arg_t);
 bool it_navigate_marked(arg_t);
 bool it_scroll_move(arg_t);
 bool it_scroll_screen(arg_t);

config.def.h

@@ -95,6 +95,7 @@ static const keymap_t keys[] = {
 	{ true,   XK_space,         i_toggle_animation,   (arg_t) None },
 
 	{ false,  XK_m,             it_toggle_image_mark, (arg_t) None },
+	{ false,  XK_M,             it_reverse_marks,     (arg_t) None },
 	{ false,  XK_N,             it_navigate_marked,   (arg_t) +1 },
 	{ false,  XK_P,             it_navigate_marked,   (arg_t) -1 },
 

sxiv.1

@@ -130,6 +130,9 @@ Remove current image from file list and go to next image.
 .B m
 Mark/unmark the current image.
 .TP
+.B M
+Reverse marked images.
+.TP
 .B N
 Go
 .I count