init.c

#include "def.h"
#include <stdlib.h>

// Since our general hash function only generate random numbers upto 0 to 15 bits so to get 64 bit random numbers
// int the second time we generatete first random 15 bits and shift them 15 to the left so the next 15 bits are filled
// and similarly for the third set of fifteen bits and then for the remaning last four bits fianlly we add them all to
// get a 64 bit no.
#define rand_64 ((ULL)rand() | (ULL)rand() << 15 | (ULL)rand() << 30 | ((ULL)rand() << 45 | ((ULL)rand() & 0xf) << 60))

int sq120to64[SQNO];
int sq64to120[64];
ULL HashKey[13][120];  // To store a random 64bit no which states that that type of element is present on that sq no.
ULL SideKey;           // To store a random numbeer if it is the turn of white in the game.
ULL CastleKey[16];     // To store 64  bits random numbers which represent each possible type of castlepositions which are
                       // 0 to 15.
int FileNo[SQNO];
int RankNo[SQNO];

// Converts the 120 size board squares to respective 0 to 63 suqares for the 64 size board and vice versa.
void Convert()
{
    int sq64 = 0;
    int sq120 = 21;
    for (int i = 0; i < 120; i++)
    {
        sq120to64[i] = 65;  // Give some invalid index for outof bound indexes.
    }

    for (int i = 0; i < 64; i++)
    {
        sq64to120[i] = 120;  // Same as above.
    }

    for (int rank = 0; rank < 8; rank++)
    {
        for (int file = 0; file < 8; file++)
        {
            sq120 =
                fr2sq(file,
                      rank);  // Move across ranks and files and convert the respective indexes to 120 based squares.
            sq120to64[sq120] =
                sq64;  // Then at that index give the value of square value at 64 size board and vice versa.
            sq64to120[sq64] = sq120;
            sq64++;
        }
    }
}

void InitHashKey()
{
    for (int i = 0; i < 13; i++)
    {
        for (int j = 0; j < 120; j++)
        {
            HashKey[i][j] = rand_64;
        }
    }
    SideKey = rand_64;
    for (int i = 0; i < 16; i++)
    {
        CastleKey[i] = rand_64;
    }
}

// This function initializes our RankNo and FileNo array wihch for any given 12 based square as an index
// will give its rank and file.
void InitializeFileAndRanks()
{
    // First initializes everything to Offboard.
    for (int i = 0; i < 120; i++)
    {
        FileNo[i] = OFF, RankNo[i] = OFF;
    }

    // Assingn the respective values to the inner board.
    for (int rank = RANK_1; rank <= RANK_8; rank++)
    {
        for (int file = FILE_A; file <= FILE_H; file++)
        {
            int sq = fr2sq(file, rank);
            FileNo[sq] = file;
            RankNo[sq] = rank;
        }
    }
}

// Initializies everythig.
void AllInit()
{
    Convert();
    InitHashKey();
    InitializeFileAndRanks();
    InitMvvLva();
}