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Store sequence numbers more compactly

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Store them and ef_type in bit-fields.

Allocate eight bits for ef_type.  Values range from 0 to EF_GAME
(currently 16), so this is plenty.

Allocate twelve bits for sequence numbers.  Sequence number mismatches
are now missed when the numbers are equal modulo 2^12.  Still
sufficiently improbable.

Common machines store the bit-fields in a 32 bit word.  There are
twelve bits left in that word for future use.  Total savings 16 bits,
which is exactly what the previous commit spent on wider uids on
common machines.
This commit is contained in:
Markus Armbruster 2009-12-31 10:30:54 +01:00
parent ba2044be18
commit 358aee203e
15 changed files with 33 additions and 34 deletions
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4
include/plane.h
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@ -46,9 +46,9 @@
struct plnstr {
/* initial part must match struct empobj */
short ef_type;
signed ef_type: 8;
unsigned pln_seqno: 12;
int pln_uid; /* unit id (plane #) */
unsigned pln_seqno;
time_t pln_timestamp; /* Last time this plane was touched */
natid pln_own; /* owning country */
coord pln_x; /* plane x-y */