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/*
This file is part of ctak.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with ctak. If not, see <https://www.gnu.org/licenses/>.
*/
#include "zobrist.h"
#include "xorshift64.h"
// ===================================================================
// Variables
// ===================================================================
static uint64_t *zobrist;
// ===================================================================
// Exported method implementations
// ===================================================================
int zobrist_init(const uint8_t board_size) {
if (zobrist != NULL)
return EXIT_FAILURE;
zobrist = malloc(sizeof(uint64_t) * board_size * board_size * (15 * 2 * 3));
// TODO: trap errno
for (int k = 0; k < board_size * board_size * (15 * 2 * 3); k++) {
zobrist[k] = rand64();
}
return EXIT_SUCCESS;
}
void zobrist_free(void) {
if (zobrist != NULL) {
free(zobrist);
zobrist = NULL;
}
}
// a position's value is from the perspective of the player to move, which flips
// with parity, so we must track this
#define PLY_PARITY_MAGIC 0x9E3779B97F4A7C15ULL
uint64_t zobrist_compute(tak_state_p state) {
uint64_t hash = 0;
for (uint8_t l = 0; l < state->board_size * state->board_size; l++) {
colour_stack_t c = state->colours[l];
const uint8_t count = COUNT_AT(state, l);
enum STONE_VARIANT s = STONE_AT(state, l);
for (uint8_t h = 0; h < count; h++, c >>= 1)
hash ^= zobrist[l * (15 * 2 * 3) + h * 2 * 3 + (c & 1) * 3 + s];
}
return hash ^ ((state->ply & 1) ? PLY_PARITY_MAGIC : 0);
}
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