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Use 32 bit key in TT

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Shrink key to 32 bits instead of 64. To still avoid
collisions use the high 32 bits of position key as the
TT key and the low 32 bits to retrieve the correct
cluster index in the table.

With this patch size og TTentry shrinks to 96 bits instead
of 128 and the cluster of 4 TTEntry sums to 48 bytes instead
of 64.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba
2009-08-09 04:19:32 +01:00
parent 4a777954e1
commit 6f1475b6fc
2 changed files with 29 additions and 22 deletions
Download Patch File Download Diff File Expand all files Collapse all files

35
src/tt.cpp
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@@ -30,6 +30,10 @@
#include "tt.h"
/// This is the number of TTEntry slots for each position
static const int ClusterSize = 4;
////
//// Functions
////
@@ -56,16 +60,16 @@ void TranspositionTable::set_size(unsigned mbSize) {
unsigned newSize = 1024;
// We store a cluster of 4 TTEntry for each position and newSize is
// the maximum number of storable positions
while ((2 * newSize) * 4 * (sizeof(TTEntry)) <= (mbSize << 20))
// We store a cluster of ClusterSize number of TTEntry for each position
// and newSize is the maximum number of storable positions.
while ((2 * newSize) * ClusterSize * (sizeof(TTEntry)) <= (mbSize << 20))
newSize *= 2;
if (newSize != size)
{
size = newSize;
delete [] entries;
entries = new TTEntry[size * 4];
entries = new TTEntry[size * ClusterSize];
if (!entries)
{
std::cerr << "Failed to allocate " << mbSize
@@ -84,7 +88,7 @@ void TranspositionTable::set_size(unsigned mbSize) {
void TranspositionTable::clear() {
memset(entries, 0, size * 4 * sizeof(TTEntry));
memset(entries, 0, size * ClusterSize * sizeof(TTEntry));
}
@@ -101,11 +105,12 @@ void TranspositionTable::clear() {
void TranspositionTable::store(const Key posKey, Value v, ValueType t, Depth d, Move m) {
TTEntry *tte, *replace;
uint32_t posKey32 = posKey >> 32; // Use the high 32 bits as key
tte = replace = first_entry(posKey);
for (int i = 0; i < 4; i++, tte++)
for (int i = 0; i < ClusterSize; i++, tte++)
{
if (!tte->key() || tte->key() == posKey) // empty or overwrite old
if (!tte->key() || tte->key() == posKey32) // empty or overwrite old
{
// Do not overwrite when new type is VALUE_TYPE_EVAL
if (tte->key() && t == VALUE_TYPE_EVAL)
@@ -114,7 +119,7 @@ void TranspositionTable::store(const Key posKey, Value v, ValueType t, Depth d,
if (m == MOVE_NONE)
m = tte->move();
*tte = TTEntry(posKey, v, t, d, m, generation);
*tte = TTEntry(posKey32, v, t, d, m, generation);
return;
}
else if (i == 0) // replace would be a no-op in this common case
@@ -127,7 +132,7 @@ void TranspositionTable::store(const Key posKey, Value v, ValueType t, Depth d,
if (c1 + c2 + c3 > 0)
replace = tte;
}
*replace = TTEntry(posKey, v, t, d, m, generation);
*replace = TTEntry(posKey32, v, t, d, m, generation);
writes++;
}
@@ -138,10 +143,11 @@ void TranspositionTable::store(const Key posKey, Value v, ValueType t, Depth d,
TTEntry* TranspositionTable::retrieve(const Key posKey) const {
uint32_t posKey32 = posKey >> 32;
TTEntry *tte = first_entry(posKey);
for (int i = 0; i < 4; i++, tte++)
if (tte->key() == posKey)
for (int i = 0; i < ClusterSize; i++, tte++)
if (tte->key() == posKey32)
return tte;
return NULL;
@@ -149,11 +155,12 @@ TTEntry* TranspositionTable::retrieve(const Key posKey) const {
/// TranspositionTable::first_entry returns a pointer to the first
/// entry of a cluster given a position.
/// entry of a cluster given a position. The low 32 bits of the key
/// are used to get the index in the table.
inline TTEntry* TranspositionTable::first_entry(const Key posKey) const {
return entries + (int(posKey & (size - 1)) << 2);
return entries + ((uint32_t(posKey) & (size - 1)) * ClusterSize);
}
/// TranspositionTable::new_search() is called at the beginning of every new
@@ -224,6 +231,6 @@ void TranspositionTable::extract_pv(const Position& pos, Move pv[]) {
int TranspositionTable::full() const {
double N = double(size) * 4.0;
double N = double(size) * ClusterSize;
return int(1000 * (1 - exp(writes * log(1.0 - 1.0/N))));
}