for (int i = 0; i < ClusterSize; ++i)
if (tte[i].key16 == key16 || !tte[i].depth8)
{
- tte[i].genBound8 = uint8_t(generation8 | (tte[i].genBound8 & 0x7)); // Refresh
+ tte[i].genBound8 = uint8_t(generation8 | (tte[i].genBound8 & (GENERATION_DELTA - 1))); // Refresh
return found = (bool)tte[i].depth8, &tte[i];
}
TTEntry* replace = tte;
for (int i = 1; i < ClusterSize; ++i)
// Due to our packed storage format for generation and its cyclic
- // nature we add 263 (256 is the modulus plus 7 to keep the unrelated
- // lowest three bits from affecting the result) to calculate the entry
- // age correctly even after generation8 overflows into the next cycle.
- if ( replace->depth8 - ((263 + generation8 - replace->genBound8) & 0xF8)
- > tte[i].depth8 - ((263 + generation8 - tte[i].genBound8) & 0xF8))
+ // nature we add GENERATION_CYCLE (256 is the modulus, plus what
+ // is needed to keep the unrelated lowest n bits from affecting
+ // the result) to calculate the entry age correctly even after
+ // generation8 overflows into the next cycle.
+ if ( replace->depth8 - ((GENERATION_CYCLE + generation8 - replace->genBound8) & GENERATION_MASK)
+ > tte[i].depth8 - ((GENERATION_CYCLE + generation8 - tte[i].genBound8) & GENERATION_MASK))
replace = &tte[i];
return found = false, replace;
int cnt = 0;
for (int i = 0; i < 1000; ++i)
for (int j = 0; j < ClusterSize; ++j)
- cnt += table[i].entry[j].depth8 && (table[i].entry[j].genBound8 & 0xF8) == generation8;
+ cnt += table[i].entry[j].depth8 && (table[i].entry[j].genBound8 & GENERATION_MASK) == generation8;
return cnt / ClusterSize;
}
static_assert(sizeof(Cluster) == 32, "Unexpected Cluster size");
+ // Constants used to refresh the hash table periodically
+ static constexpr unsigned GENERATION_BITS = 3; // nb of bits reserved for other things
+ static constexpr int GENERATION_DELTA = (1 << GENERATION_BITS); // increment for generation field
+ static constexpr int GENERATION_CYCLE = 255 + (1 << GENERATION_BITS); // cycle length
+ static constexpr int GENERATION_MASK = (0xFF << GENERATION_BITS) & 0xFF; // mask to pull out generation number
+
public:
~TranspositionTable() { aligned_large_pages_free(table); }
- void new_search() { generation8 += 8; } // Lower 3 bits are used by PV flag and Bound
+ void new_search() { generation8 += GENERATION_DELTA; } // Lower bits are used for other things
TTEntry* probe(const Key key, bool& found) const;
int hashfull() const;
void resize(size_t mbSize);