1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192
|
#include <stdio.h>
#include <stdlib.h>
#include "chess.h"
#include "data.h"
/* last modified 03/07/97 */
/*
********************************************************************************
* *
* Swap() is used to analyze capture moves to see whether or not they appear *
* to be profitable. the basic algorithm is extremely fast since it uses the *
* bitmaps to determine which squares are attacking the [target] square. *
* *
* the algorithm is quite simple. using the attack bitmaps, we enumerate all *
* the pieces that are attacking [target] for either side. then we simply *
* use the lowest piece (value) for the correct side to capture on [target]. *
* we continually "flip" sides taking the lowest piece each time. *
* *
* as a piece is used, if it is a sliding piece (pawn, bishop, rook or queen) *
* we "peek" behind it to see if it is attacked by a sliding piece in the *
* direction away from the piece being captured. if so, and that sliding *
* piece moves in this direction, then it is added to the list of attackers *
* since its attack has been "uncovered" by moving the capturing piece. *
* *
********************************************************************************
*/
int Swap(TREE *tree, int source, int target, int wtm)
{
register BITBOARD attacks;
register int attacked_piece;
register int square, direction;
register int sign, color, next_capture=1;
int swap_list[32];
/*
----------------------------------------------------------
| |
| determine which squares attack <target> for each side. |
| |
----------------------------------------------------------
*/
attacks=AttacksTo(tree,target);
/*
----------------------------------------------------------
| |
| initialize by placing the piece on <target> first in |
| the list as it is being captured to start things off. |
| |
----------------------------------------------------------
*/
attacked_piece=p_values[PieceOnSquare(target)+7];
/*
----------------------------------------------------------
| |
| the first piece to capture on <target> is the piece |
| standing on <source>. |
| |
----------------------------------------------------------
*/
color=ChangeSide(wtm);
swap_list[0]=attacked_piece;
sign=-1;
attacked_piece=p_values[PieceOnSquare(source)+7];
Clear(source,attacks);
direction=directions[target][source];
if (direction) attacks=SwapXray(tree,attacks,source,direction);
/*
----------------------------------------------------------
| |
| now pick out the least valuable piece for the correct |
| side that is bearing on <target>. as we find one, we |
| call SwapXray() to add the piece behind this piece |
| that is indirectly bearing on <target> (if any). |
| |
----------------------------------------------------------
*/
while (attacks) {
if (color) {
if (And(WhitePawns,attacks))
square=FirstOne(And(WhitePawns,attacks));
else if (And(WhiteKnights,attacks))
square=FirstOne(And(WhiteKnights,attacks));
else if (And(WhiteBishops,attacks))
square=FirstOne(And(WhiteBishops,attacks));
else if (And(WhiteRooks,attacks))
square=FirstOne(And(WhiteRooks,attacks));
else if (And(WhiteQueens,attacks))
square=FirstOne(And(WhiteQueens,attacks));
else if (And(WhiteKing,attacks))
square=WhiteKingSQ;
else break;
}
else {
if (And(BlackPawns,attacks))
square=FirstOne(And(BlackPawns,attacks));
else if (And(BlackKnights,attacks))
square=FirstOne(And(BlackKnights,attacks));
else if (And(BlackBishops,attacks))
square=FirstOne(And(BlackBishops,attacks));
else if (And(BlackRooks,attacks))
square=FirstOne(And(BlackRooks,attacks));
else if (And(BlackQueens,attacks))
square=FirstOne(And(BlackQueens,attacks));
else if (And(BlackKing,attacks))
square=BlackKingSQ;
else break;
}
/*
------------------------------------------------
| |
| located the least valuable piece bearing on |
| <target>. remove it from the list and then |
| find out if a sliding piece behind it attacks |
| through this piece. |
| |
------------------------------------------------
*/
swap_list[next_capture]=swap_list[next_capture-1]+sign*attacked_piece;
attacked_piece=p_values[PieceOnSquare(square)+7];
Clear(square,attacks);
direction=directions[target][square];
if (direction) attacks=SwapXray(tree,attacks,square,direction);
next_capture++;
sign=-sign;
color=ChangeSide(color);
}
/*
----------------------------------------------------------
| |
| starting at the end of the sequence of values, use a |
| "minimax" like procedure to decide where the captures |
| will stop. |
| |
----------------------------------------------------------
*/
next_capture--;
if(next_capture&1) sign=-1;
else sign=1;
while (next_capture) {
if (sign < 0) {
if(swap_list[next_capture] <= swap_list[next_capture-1])
swap_list[next_capture-1]=swap_list[next_capture];
}
else {
if(swap_list[next_capture] >= swap_list[next_capture-1])
swap_list[next_capture-1]=swap_list[next_capture];
}
next_capture--;
sign=-sign;
}
return (swap_list[0]);
}
/*
********************************************************************************
* *
* SwapXray() is used to determine if a piece is "behind" the piece on *
* <from>, and this piece would attack <to> if the piece on <from> were moved *
* (as in playing out sequences of swaps). if so, this indirect attacker is *
* added to the list of attackers bearing to <to>. *
* *
********************************************************************************
*/
BITBOARD SwapXray(TREE *tree, BITBOARD attacks, int from, int direction)
{
switch (direction) {
case 1:
return(Or(attacks,
And(And(AttacksRank(from),RooksQueens),plus1dir[from])));
case 7:
return(Or(attacks,
And(And(AttacksDiaga1(from),BishopsQueens),plus7dir[from])));
case 8:
return(Or(attacks,
And(And(AttacksFile(from),RooksQueens),plus8dir[from])));
case 9:
return(Or(attacks,
And(And(AttacksDiagh1(from),BishopsQueens),plus9dir[from])));
case -1:
return(Or(attacks,
And(And(AttacksRank(from),RooksQueens),minus1dir[from])));
case -7:
return(Or(attacks,
And(And(AttacksDiaga1(from),BishopsQueens),minus7dir[from])));
case -8:
return(Or(attacks,
And(And(AttacksFile(from),RooksQueens),minus8dir[from])));
case -9:
return(Or(attacks,
And(And(AttacksDiagh1(from),BishopsQueens),minus9dir[from])));
}
return(attacks);
}
|