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#include "tt.h"

#include <cstdint>

#if defined(_MSC_VER)

#include <intrin.h>

#endif

using namespace engine;

static inline uint64_t index_for_hash(uint64_t hash, uint64_t buckets) {

if (buckets == 0)

return 0;

#if defined(_MSC_VER)

// MSVC: use _umul128 to get high 64 bits of 128-bit product

unsigned long long high = 0;

(void)_umul128((unsigned long long)hash, (unsigned long long)buckets, &high);

return (uint64_t)high;

#elif defined(__SIZEOF_INT128__)

// GCC/Clang: use __uint128_t

__uint128_t prod = (__uint128_t)hash * (__uint128_t)buckets;

return (uint64_t)(prod >> 64);

#else

uint64_t aL = uint32_t(hash), aH = hash >> 32;

uint64_t bL = uint32_t(buckets), bH = buckets >> 32;

uint64_t c1 = (aL * bL) >> 32;

uint64_t c2 = aH * bL + c1;

uint64_t c3 = aL * bH + uint32_t(c2);

return aH * bH + (c2 >> 32) + (c3 >> 32);

#endif

}

void TranspositionTable::newSearch() { time++; }

void TranspositionTable::store(uint64_t hash, chess::Move best, int16_t score, int8_t depth, TTFlag flag) {

// 2 entries per bucket

if (buckets == 0)

return;

uint64_t index = index_for_hash(hash, buckets);

TTEntry &e0 = table[2 * index], &e1 = table[2 * index + 1];

// Store the entry

for (TTEntry *e : { &e0, &e1 }) {

if (e->key == hash || e->getDepth() < depth) {

e->key = hash;

e->setPackedFields(score, depth, flag, best.raw(), time);

return;

}

// If we get here, we need to evict an entry

// Find the oldest entry

TTEntry *oldest = (e0.timestamp() < e1.timestamp()) ? &e0 : &e1;

// Evict it

oldest->key = hash;

oldest->setPackedFields(score, depth, flag, best.raw(), time);

}

TTEntry *TranspositionTable::lookup(uint64_t hash) {

if (buckets == 0 || hash == 0)

return nullptr;

uint64_t bucket = index_for_hash(hash, buckets);

TTEntry &e0 = table[2 * bucket];

TTEntry &e1 = table[2 * bucket + 1];

if (e0.key == hash)

return &e0;

if (e1.key == hash)

return &e1;

return nullptr;

}