Clamp motion vectors at frame level

This fixes bitstream corruption!

Lost hours here: many.

Author: rom1v

src/context.rs

@@ -2610,16 +2610,20 @@ impl<'a> ContextWriter<'a> {
 
     /* TODO: Handle single reference frame extension */
 
+    let frame_bo = BlockOffset {
+      x: self.bc.blocks.x() + bo.x,
+      y: self.bc.blocks.y() + bo.y,
+    };
     // clamp mvs
     for mv in mv_stack {
       let blk_w = bsize.width();
       let blk_h = bsize.height();
       let border_w = 128 + blk_w as isize * 8;
       let border_h = 128 + blk_h as isize * 8;
-      let mvx_min = -(bo.x as isize) * (8 * MI_SIZE) as isize - border_w;
-      let mvx_max = (self.bc.blocks.cols() - bo.x - blk_w / MI_SIZE) as isize * (8 * MI_SIZE) as isize + border_w;
-      let mvy_min = -(bo.y as isize) * (8 * MI_SIZE) as isize - border_h;
-      let mvy_max = (self.bc.blocks.rows() - bo.y - blk_h / MI_SIZE) as isize * (8 * MI_SIZE) as isize + border_h;
+      let mvx_min = -(frame_bo.x as isize) * (8 * MI_SIZE) as isize - border_w;
+      let mvx_max = (self.bc.blocks.frame_cols - frame_bo.x - blk_w / MI_SIZE) as isize * (8 * MI_SIZE) as isize + border_w;
+      let mvy_min = -(frame_bo.y as isize) * (8 * MI_SIZE) as isize - border_h;
+      let mvy_max = (self.bc.blocks.frame_rows - frame_bo.y - blk_h / MI_SIZE) as isize * (8 * MI_SIZE) as isize + border_h;
       mv.this_mv.row = (mv.this_mv.row as isize).max(mvy_min).min(mvy_max) as i16;
       mv.this_mv.col = (mv.this_mv.col as isize).max(mvx_min).min(mvx_max) as i16;
       mv.comp_mv.row = (mv.comp_mv.row as isize).max(mvy_min).min(mvy_max) as i16;