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Use last_1() to compute new TT size

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Transposition table consists of a power of 2
number of TTCluster entries.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2012-07-07 19:30:27 +01:00
parent 089e54c7fd
commit 67d91dfd50
1 changed files with 8 additions and 10 deletions
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18
src/tt.cpp
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@ -20,6 +20,7 @@
#include <cstring>
#include <iostream>
#include "bitboard.h"
#include "tt.h"
TranspositionTable TT; // Our global transposition table
@ -37,18 +38,13 @@ TranspositionTable::~TranspositionTable() {
/// TranspositionTable::set_size() sets the size of the transposition table,
/// measured in megabytes.
/// measured in megabytes. Transposition table consists of a power of 2 number of
/// TTCluster and each cluster consists of ClusterSize number of TTEntries. Each
/// non-empty entry contains information of exactly one position.
void TranspositionTable::set_size(size_t mbSize) {
size_t newSize = 1024;
// Transposition table consists of clusters and each cluster consists
// of ClusterSize number of TTEntries. Each non-empty entry contains
// information of exactly one position and newSize is the number of
// clusters we are going to allocate.
while (2ULL * newSize * sizeof(TTCluster) <= (mbSize << 20))
newSize *= 2;
size_t newSize = 1ULL << last_1((mbSize << 20) / sizeof(TTCluster));
if (newSize == size)
return;
@ -56,13 +52,15 @@ void TranspositionTable::set_size(size_t mbSize) {
size = newSize;
delete [] entries;
entries = new (std::nothrow) TTCluster[size];
if (!entries)
{
std::cerr << "Failed to allocate " << mbSize
<< "MB for transposition table." << std::endl;
exit(EXIT_FAILURE);
}
clear();
clear(); // operator new is not guaranteed to initialize memory to zero
}