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/*
  This file is part of ct.

  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 ct. If not, see <https://www.gnu.org/licenses/>.
*/

#include "zobrist.h"

// ===================================================================
// Variables
// ===================================================================

static uint64_t *zobrist;

// ===================================================================
// Exported method implementations
// ===================================================================

int zobrist_init(void) {
  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++) {
    XORSHIFT64;
    zobrist[k] = RANDOM64;
  }

  return EXIT_SUCCESS;
}

void zobrist_free(void) {
  if (zobrist != NULL) {
    free(zobrist);
    zobrist = NULL;
  }
}

uint64_t zobrist_compute(void) {
  uint64_t hash = 0;
  for (uint8_t l=0; l<board_size*board_size; l++) {
    colour_stack_t c = colours[l];
    const uint8_t count = COUNT_AT(l);
    enum STONE_VARIANT s = STONE_AT(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;
}