ring: Simplify calculation of number of frames in a tpacket ring

The number of frames in a tpacket ring (ring->layout.tp_frame_nr) is
currently calculated as:

  tp_frame_nr = tp_block_size / tp_frame_size * tp_block_nr

Substituting tp_block_nr with 'size / tp_block_size' (as calculated in
the line above), we get:

  tp_frame_nr = tp_block_size / tp_frame_size * (size / tp_block_size)

and realize that we can omit tp_block_size as it cancels out, leading
to:

  tp_frame_nr = 1 / tp_frame_size * (size / 1)
              = size / tp_frame_size

Adjust the calculation in setup_ring_layout_generic() accordingly.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

1 files changed, 1 insertions, 4 deletions

diff --git a/ring.c b/ring.c
index 26de18e..dc58a07 100644
--- a/ring.c
+++ b/ring.c
@@ -34,10 +34,7 @@ void setup_ring_layout_generic(int sock, struct ring *ring, size_t size,
 				      TPACKET_ALIGNMENT << 7);
 
 	ring->layout.tp_block_nr = size / ring->layout.tp_block_size;
-	ring->layout.tp_frame_nr = ring->layout.tp_block_size /
-				   ring->layout.tp_frame_size *
-				   ring->layout.tp_block_nr;
-
+	ring->layout.tp_frame_nr = size / ring->layout.tp_frame_size;
 }
 
 void mmap_ring_generic(int sock, struct ring *ring)