Author: Bo Persson
Date: 03:49:49 01/03/04
Go up one level in this thread
On January 02, 2004 at 21:52:56, Federico Corigliano wrote:
>My current hash entry uses a struct and needs 40 bits. I calculated that I can
>optimize the size using two unsigned 64 bits integers with the following
>distribution:
>
>struct hashEntry {
> uint64 a;
> uint64 b;
>};
>
>Name Bits Description Access
>--------------------------------------------------------------------------------
>Hash key 64 Hash key signature (entry.a)
>Depth 10 Position's search depth* (entry.b >> 54)
>Score 16 Position's score (-32767...32767) (entry.b >> 38) & 0xffff
>Move 32 Position's best move (entry.b >> 6) & 0xffffffff
>Age 3 Position's age (entry.b >> 3) & 0x7
>Threat 1 Threat's extension flag (entry.b >> 2) & 0x1
>Type 2 Upper, lower, exact or none (entry.b & 0x3)
>---------------
>Total: 128 (16 bytes)
>
>* I use a value of 16 for a full ply, so the max search depth is 63, pretty
>sufficient.
You can gain some additional bits by not storing the entire hash key. If you,
for example, always have at least 2^16 entries in your hash table and use the
lower 16 bits as the address, you then know that these bits always match so you
only have to store the remaning 48 bits in the hash entry.
Bo Persson
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