Sure, straight enums use more space, but it's possible to use an enum
bitfield. That would get the best of both worlds.
Eddie
Arnaldo Carvalho de Melo wrote:
On 11/15/06, Gerrit Renker <gerrit@xxxxxxxxxxxxxx> wrote:
This patch tackles the following problem:
* the ccid3_hc_{t,r}x_sock define ccid3hc{t,r}x_state as `u8',
but
in reality there can only be a few, pre-defined enum names
* this necessitates addiditional checking for unexpected values
which would otherwise be caught by the compiler
My problem is with the changes to the structs, from u8 to enums, that
take 4 bytes, <shameless plug>see using my new tool, codiff (code
diff):
[acme@newtoy net-2.6.20]$ codiff --structs --verbose
/tmp/ccid3.o.before /tmp/ccid3.o.enum
/pub/scm/linux/kernel/git/acme/net-2.6.20/net/dccp/ccids/ccid3.c:
struct ccid3_hc_tx_sock | +4
ccid3hctx_state;
from: u8 /* 30(0) 1(0) */
to: enum ccid3_hc_tx_states /* 32(0) 4(0) */
struct ccid3_hc_rx_sock | +4
ccid3hcrx_state:8;
from: u64 /* 16(36) 8(8) */
to: enum ccid3_hc_rx_states /* 20(0) 4(0) */
2 structs changed
[acme@newtoy net-2.6.20]$
</shameless plug>
I removed the other parts of the patch (replacing printks+dump_stack
with BUG) to see what would be the code impact of such change and was
surprised:
[acme@newtoy net-2.6.20]$ codiff --functions /tmp/ccid3.o.before
/tmp/ccid3.o.enum
/pub/scm/linux/kernel/git/acme/net-2.6.20/net/dccp/ccids/ccid3.c:
ccid3_hc_rx_set_state | -33
ccid3_hc_tx_set_state | -5
ccid3_hc_rx_send_feedback | -16
ccid3_hc_rx_init | -8
ccid3_hc_tx_init | +3
ccid3_hc_tx_no_feedback_timer | -14
ccid3_hc_rx_packet_recv | -48
ccid3_hc_rx_get_info | -5
8 functions changed, 3 bytes added, 129 bytes removed
[acme@newtoy net-2.6.20]$
Anyway, there are always tradeoffs, compiler gets more info, but we
end up using more memory per socket instance, I guess we can stay like
we are now, no? :-)
- Arnaldo
Probably because we stop using a u64 bitfield in the rx case...
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