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midgame.c
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/*
File: midgame.c
Created: July 1, 1997
Modified: November 23, 2002
Author: Gunnar Andersson ([email protected])
Contents: Search routines designated to be used in the
midgame phase of the game.
*/
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include "autoplay.h"
#include "constant.h"
#include "display.h"
#include "eval.h"
#include "getcoeff.h"
#include "globals.h"
#include "hash.h"
#include "macros.h"
#include "midgame.h"
#include "moves.h"
#include "myrandom.h"
#include "patterns.h"
#include "pcstat.h"
#include "probcut.h"
#include "search.h"
#include "texts.h"
#include "timer.h"
/* Enable/disable Multi-ProbCut */
#define USE_MPC 1
/* Number of nodes searched between consecutive time checks */
#ifdef _WIN32_WCE
#define EVENT_CHECK_INTERVAL 10000
#else
#define EVENT_CHECK_INTERVAL 100000
#endif
/* The eval bonus given if the hash table move is found during the
shallow search. */
#define HASH_MOVE_BONUS 10000
/* The depth from which where hash tables lookups are performed. */
#define HASH_THRESHOLD 2
/* The depth where shallow searches are first performed. */
#define PRE_SEARCH_THRESHOLD 3
/* The depth to which all variations must be searched */
#define FULL_WIDTH_DEPTH 8
/* The depth where shallow searches are performed to depth 2. */
#define DEPTH_TWO_DEPTH 10
/* Default aspiration window parameters. These values are currently
really huge as usage of a small windows tends to slow down
the search. */
#define USE_WINDOW FALSE
#define ALPHA_WINDOW 2048
#define BETA_WINDOW 2048
#define WIPEOUT_THRESHOLD 60
static int allow_midgame_hash_probe;
static int allow_midgame_hash_update;
static int best_mid_move, best_mid_root_move;
static int midgame_abort;
static int do_check_midgame_abort = TRUE;
static int counter_phase;
static int apply_perturbation = TRUE;
static int perturbation_amplitude = 0;
static int stage_reached[61], stage_score[61];
static int score_perturbation[100];
static int feas_index_list[64][64];
/*
SETUP_MIDGAME
Sets up some search parameters.
*/
void
setup_midgame( void ) {
int i;
allow_midgame_hash_probe = TRUE;
allow_midgame_hash_update = TRUE;
for ( i = 0; i <= 60; i++ )
stage_reached[i] = FALSE;
calculate_perturbation();
}
/*
CLEAR_MIDGAME_ABORT
IS_MIDGAME_ABORT
SET_MIDGAME_ABORT
TOGGLE_MIDGAME_ABORT_CHECK
These functions handle the midgame abort system which kicks in
when it is estimated that the next iteration in the iterative
deepening would take too long.
*/
void
clear_midgame_abort( void ) {
midgame_abort = FALSE;
}
int
is_midgame_abort( void ) {
return midgame_abort;
}
void
set_midgame_abort( void ) {
midgame_abort = do_check_midgame_abort;
}
void
toggle_midgame_abort_check( int toggle ) {
do_check_midgame_abort = toggle;
}
/*
TOGGLE_MIDGAME_HASH_USAGE
Toggles hash table access in the midgame search on/off.
*/
void
toggle_midgame_hash_usage( int allow_read, int allow_write ) {
allow_midgame_hash_probe = allow_read;
allow_midgame_hash_update = allow_write;
}
/*
CALCULATE_PERTURBATION
Determines the score perturbations (if any) to the root moves.
*/
void
calculate_perturbation( void ) {
int i;
int shift;
if ( !apply_perturbation || (perturbation_amplitude == 0) )
for ( i = 0; i < 100; i++ )
score_perturbation[i] = 0;
else {
shift = perturbation_amplitude / 2;
for ( i = 0; i < 100; i++ )
score_perturbation[i] =
(abs( my_random()) % perturbation_amplitude) - shift;
}
}
/*
SET_PERTURBATION
Set the amplitude of the score perturbation applied by
CALCULATE_PERTURBATION.
*/
void
set_perturbation( int amplitude ) {
perturbation_amplitude = amplitude;
}
/*
TOGGLE_PERTURBATION_USAGE
Toggle usage of score perturbations on/off.
*/
void
toggle_perturbation_usage( int toggle ) {
apply_perturbation = toggle;
}
/*
ADVANCE_MOVE
Swaps a move and its predecessor in the move list if it's
not already first in the list.
*/
INLINE static
void
advance_move( int index ) {
int temp_move;
if ( index > 0 ) {
temp_move = sorted_move_order[disks_played][index];
sorted_move_order[disks_played][index] =
sorted_move_order[disks_played][index - 1];
sorted_move_order[disks_played][index - 1] = temp_move;
}
}
/*
STATIC_OR_TERMINAL_EVALUATION
Invokes the proper evaluation function depending on whether the
board is filled or not.
*/
INLINE static int
static_or_terminal_evaluation( int side_to_move ) {
if ( disks_played == 60 )
return terminal_evaluation( side_to_move );
else
return static_evaluation( side_to_move );
}
/*
FAST_TREE_SEARCH
The recursive tree search function. It uses negascout for
tree pruning.
*/
static int
fast_tree_search( int level, int max_depth, int side_to_move, int alpha,
int beta, int allow_hash, int void_legal ) {
int curr_val, best;
int move_index, move;
int best_move_index, best_move;
int first;
int remains;
int use_hash, new_use_hash;
int curr_alpha;
int empties_remaining;
HashEntry entry;
INCREMENT_COUNTER( nodes );
if ( level >= max_depth )
return static_or_terminal_evaluation( side_to_move );
/* Check the hash table */
remains = max_depth - level;
use_hash = (remains >= HASH_THRESHOLD) && USE_HASH_TABLE && allow_hash;
if ( use_hash && allow_midgame_hash_probe ) {
find_hash( &entry, MIDGAME_MODE );
if ( (entry.draft >= remains) &&
(entry.selectivity == 0) &&
valid_move( entry.move[0], side_to_move ) &&
(entry.flags & MIDGAME_SCORE) &&
((entry.flags & EXACT_VALUE) ||
((entry.flags & LOWER_BOUND) && entry.eval >= beta) ||
((entry.flags & UPPER_BOUND) && entry.eval <= alpha)) ) {
best_mid_move = entry.move[0];
return entry.eval;
}
}
/* Reorder the move lists now and then to keep the empty squares up front */
if ( (nodes.lo & 4095) == 0 )
reorder_move_list( disks_played );
/* Search */
first = TRUE;
best_move = PASS;
best_move_index = -1;
best = -INFINITE_EVAL;
if ( remains == 1 ) { /* Plain alpha-beta last ply */
empties_remaining = 60 - disks_played;
for ( move_index = 0; move_index < MOVE_ORDER_SIZE; move_index++ ) {
move = sorted_move_order[disks_played][move_index];
if ( board[move] == EMPTY ) {
if ( make_move_no_hash( side_to_move, move ) != 0 ) {
curr_val = -static_or_terminal_evaluation( OPP( side_to_move ) );
unmake_move_no_hash( side_to_move, move );
INCREMENT_COUNTER( nodes );
if ( curr_val > best ) {
best = curr_val;
best_move_index = move_index;
best_move = move;
if ( curr_val >= beta ) {
advance_move( move_index );
best_mid_move = best_move;
if ( use_hash && allow_midgame_hash_update )
add_hash( MIDGAME_MODE, best, best_move,
MIDGAME_SCORE | LOWER_BOUND, remains, 0 );
return best;
}
}
first = FALSE;
}
empties_remaining--;
if ( empties_remaining == 0 )
break;
}
}
}
else { /* Principal variation search for deeper searches */
new_use_hash = (remains >= HASH_THRESHOLD + 1) && use_hash;
curr_alpha = alpha;
empties_remaining = 60 - disks_played;
for ( move_index = 0; move_index < MOVE_ORDER_SIZE; move_index++ ) {
move = sorted_move_order[disks_played][move_index];
if ( board[move] == EMPTY ) {
if ( make_move( side_to_move, move, new_use_hash ) != 0 ) {
if ( first ) {
best = curr_val =
-fast_tree_search( level + 1, max_depth, OPP( side_to_move ),
-beta, -curr_alpha, allow_hash, TRUE );
best_move = move;
best_move_index = move_index;
}
else {
curr_alpha = MAX( best, curr_alpha );
curr_val =
-fast_tree_search( level + 1, max_depth, OPP( side_to_move ),
-(curr_alpha + 1), -curr_alpha, allow_hash,
TRUE );
if ( (curr_val > curr_alpha) && (curr_val < beta) )
curr_val =
-fast_tree_search( level + 1, max_depth, OPP( side_to_move ),
-beta, INFINITE_EVAL, allow_hash, TRUE );
if ( curr_val > best ) {
best_move = move;
best_move_index = move_index;
best = curr_val;
}
}
unmake_move( side_to_move, move );
if ( best >= beta ) {
advance_move( move_index );
best_mid_move = best_move;
if ( use_hash && allow_midgame_hash_update )
add_hash( MIDGAME_MODE, best, best_move,
MIDGAME_SCORE | LOWER_BOUND, remains, 0 );
return best;
}
first = FALSE;
}
empties_remaining--;
if ( empties_remaining == 0 )
break;
}
}
}
if ( !first ) {
advance_move( best_move_index );
best_mid_move = best_move;
if ( use_hash && allow_midgame_hash_update ) {
if ( best > alpha )
add_hash( MIDGAME_MODE, best, best_move,
MIDGAME_SCORE | EXACT_VALUE, remains, 0 );
else
add_hash( MIDGAME_MODE, best, best_move,
MIDGAME_SCORE | UPPER_BOUND, remains, 0 );
}
return best;
}
else if ( void_legal ) { /* I pass, other player's turn now */
hash1 ^= hash_flip_color1;
hash2 ^= hash_flip_color2;
curr_val = -fast_tree_search( level, max_depth, OPP( side_to_move ),
-beta, -alpha, allow_hash, FALSE );
hash1 ^= hash_flip_color1;
hash2 ^= hash_flip_color2;
return curr_val;
}
else { /* Both players had to pass ==> evaluate board as final */
curr_val = terminal_evaluation( side_to_move );
return curr_val;
}
}
#define VERBOSE 0
/*
UPDATE_BEST_LIST
*/
static void
update_best_list( int *best_list, int move, int best_list_index,
int best_list_length ) {
int i;
#if VERBOSE
printf( "move=%2d index=%d length=%d ", move, best_list_index,
best_list_length );
printf( "Before: " );
for ( i = 0; i < 4; i++ )
printf( "%2d ", best_list[i] );
#endif
if ( best_list_index < best_list_length )
for ( i = best_list_index; i >= 1; i-- )
best_list[i] = best_list[i - 1];
else
for ( i = 3; i >= 1; i-- )
best_list[i] = best_list[i - 1];
best_list[0] = move;
#if VERBOSE
printf( " After: " );
for ( i = 0; i < 4; i++ )
printf( "%2d ", best_list[i] );
puts( "" );
#endif
}
/*
TREE_SEARCH
The recursive tree search function. It uses negascout for
tree pruning.
*/
int
tree_search( int level,
int max_depth,
int side_to_move,
int alpha,
int beta,
int allow_hash,
int allow_mpc,
int void_legal ) {
int i, j;
int curr_val, best, pre_best;
int searched;
int move, hash_move;
int move_index, best_move_index;
int empties_remaining;
int hash_hit;
int pre_depth;
int update_pv;
int remains, shallow_remains;
int use_hash, pre_search_done;
int curr_alpha;
int best_index, best_score;
int best_list_index, best_list_length;
int selectivity, cut;
int best_list[4];
HashEntry entry;
#if CHECK_HASH_CODES && defined( TEXT_BASED )
unsigned int h1, h2;
#endif
if ( level >= max_depth ) {
INCREMENT_COUNTER( nodes );
return static_or_terminal_evaluation( side_to_move );
}
remains = max_depth - level;
if ( remains < PRE_SEARCH_THRESHOLD ) {
curr_val = fast_tree_search( level, max_depth, side_to_move, alpha,
beta, allow_hash, void_legal );
pv_depth[level] = level + 1;
pv[level][level] = best_mid_move;
return curr_val;
}
INCREMENT_COUNTER( nodes );
/* Check the hash table */
use_hash = (remains >= HASH_THRESHOLD) && USE_HASH_TABLE && allow_hash;
if ( USE_MPC && allow_mpc )
selectivity = 1;
else
selectivity = 0;
#if CHECK_HASH_CODES && defined( TEXT_BASED )
if ( use_hash ) {
h1 = hash1;
h2 = hash2;
}
#endif
if ( use_hash && allow_midgame_hash_probe ) {
find_hash( &entry, MIDGAME_MODE );
if ( (entry.draft >= remains) &&
(entry.selectivity <= selectivity) &&
valid_move( entry.move[0], side_to_move ) &&
(entry.flags & MIDGAME_SCORE) &&
((entry.flags & EXACT_VALUE) ||
((entry.flags & LOWER_BOUND) && entry.eval >= beta) ||
((entry.flags & UPPER_BOUND) && entry.eval <= alpha)) ) {
pv[level][level] = entry.move[0];
pv_depth[level] = level + 1;
return entry.eval;
}
}
hash_hit = (use_hash && allow_midgame_hash_probe);
if ( hash_hit )
hash_move = entry.move[0];
else
hash_move = 44;
pre_search_done = FALSE;
/* Use multi-prob-cut to selectively prune the tree */
if ( USE_MPC && allow_mpc && (remains <= MAX_CUT_DEPTH) ) {
int alpha_test = TRUE;
int beta_test = TRUE;
for ( cut = 0; cut < mpc_cut[remains].cut_tries; cut++ ) {
/* Determine the fail-high and fail-low bounds */
int bias = mpc_cut[remains].bias[cut][disks_played];
int window = mpc_cut[remains].window[cut][disks_played];
int alpha_bound = alpha + bias - window;
int beta_bound = beta + bias + window;
/* Don't use an MPC cut which results in the full-width depth
being less than some predefined constant */
shallow_remains = mpc_cut[remains].cut_depth[cut];
if ( level + shallow_remains < FULL_WIDTH_DEPTH )
continue;
if ( shallow_remains > 1 ) { /* "Deep" shallow search */
if ( cut == 0 ) {
/* Use static eval to decide if a one- or two-sided
MPC test is to be performed. */
int static_eval = static_evaluation( side_to_move );
if ( static_eval <= alpha_bound )
beta_test = FALSE;
else if ( static_eval >= beta_bound )
alpha_test = FALSE;
}
assert( alpha_test || beta_test );
if ( alpha_test && beta_test ) {
/* Test for likely fail-low or likely fail-high. */
int shallow_val =
tree_search( level, level + shallow_remains, side_to_move,
alpha_bound, beta_bound, allow_hash, FALSE,
void_legal );
if ( shallow_val >= beta_bound ) {
if ( use_hash && allow_midgame_hash_update )
add_hash( MIDGAME_MODE, beta, pv[level][level],
MIDGAME_SCORE | LOWER_BOUND, remains, selectivity );
return beta;
}
else if ( shallow_val <= alpha_bound ) {
if ( use_hash && allow_midgame_hash_update )
add_hash( MIDGAME_MODE, alpha, pv[level][level],
MIDGAME_SCORE | UPPER_BOUND, remains, selectivity );
return alpha;
}
else {
/* Use information learned from the failed cut test to decide
if a one or a two-sided test is to be performed next. */
int mid = (alpha_bound + beta_bound) / 2;
#if 0
if ( abs( shallow_val - alpha_bound ) < abs( shallow_val - mid ) )
beta_test = FALSE;
if ( abs( shallow_val - beta_bound ) < abs( shallow_val - mid ) )
alpha_test = FALSE;
#elif 1
if ( shallow_val < mid )
beta_test = FALSE;
else
alpha_test = FALSE;
#else
int low_threshold = (2 * mid + alpha_bound) / 3;
int high_threshold = (2 * mid + beta_bound) / 3;
if ( shallow_val <= low_threshold )
beta_test = FALSE;
else if ( shallow_val >= high_threshold )
alpha_test = FALSE;
else
break; /* Unlikely that there is any selective cutoff. */
#endif
}
}
else if ( beta_test ) {
/* Fail-high with high probability? */
if ( tree_search( level, level + shallow_remains, side_to_move,
beta_bound - 1, beta_bound, allow_hash, FALSE,
void_legal ) >= beta_bound ) {
if ( use_hash && allow_midgame_hash_update )
add_hash( MIDGAME_MODE, beta, pv[level][level],
MIDGAME_SCORE | LOWER_BOUND, remains, selectivity );
return beta;
}
}
else if ( alpha_test ) {
/* Fail-low with high probability? */
if ( tree_search( level, level + shallow_remains, side_to_move,
alpha_bound, alpha_bound + 1, allow_hash, FALSE,
void_legal ) <= alpha_bound ) {
if ( use_hash && allow_midgame_hash_update )
add_hash( MIDGAME_MODE, alpha, pv[level][level],
MIDGAME_SCORE | UPPER_BOUND, remains, selectivity );
return alpha;
}
}
}
else { /* All-in-one MPC one-ply search and move ordering */
move_count[disks_played] = 0;
best = alpha_bound;
empties_remaining = 60 - disks_played;
for ( move_index = 0; move_index < MOVE_ORDER_SIZE; move_index++ ) {
move = sorted_move_order[disks_played][move_index];
if ( board[move] == EMPTY ) {
if ( make_move_no_hash( side_to_move, move ) != 0 ) {
curr_val = -static_or_terminal_evaluation( OPP( side_to_move ) );
unmake_move_no_hash( side_to_move, move );
INCREMENT_COUNTER( nodes );
if ( curr_val > best ) {
best = curr_val;
if ( best >= beta_bound ) {
if ( use_hash && allow_midgame_hash_update )
add_hash( MIDGAME_MODE, beta, pv[level][level],
MIDGAME_SCORE | LOWER_BOUND, remains,
selectivity );
return beta;
}
}
evals[disks_played][move] = curr_val;
if ( move == hash_move ) /* Always try hash table move first */
evals[disks_played][move] += HASH_MOVE_BONUS;
feas_index_list[disks_played][move_count[disks_played]] =
move_index;
move_count[disks_played]++;
}
empties_remaining--;
if ( empties_remaining == 0 )
break;
}
}
if ( (best == alpha_bound) && (move_count[disks_played] > 0) ) {
if ( use_hash && allow_midgame_hash_update )
add_hash( MIDGAME_MODE, alpha, pv[level][level],
MIDGAME_SCORE | UPPER_BOUND, remains, selectivity );
return alpha;
}
pre_search_done = TRUE;
}
}
}
/* Full negascout search */
searched = 0;
best = -INFINITE_EVAL;
best_move_index = -1;
curr_alpha = alpha;
best_list_length = 0;
for ( i = 0; i < 4; i++ )
best_list[i] = 0;
if ( !pre_search_done ) {
move_count[disks_played] = 0;
if ( hash_hit )
for ( i = 0; i < 4; i++ )
if ( valid_move( entry.move[i], side_to_move ) )
best_list[best_list_length++] = entry.move[i];
}
for ( i = 0, best_list_index = 0; TRUE; i++, best_list_index++ ) {
/* Try the hash table move(s) first if feasible */
if ( !pre_search_done && (best_list_index < best_list_length) ) {
move_count[disks_played]++;
move_index = 0;
while ( sorted_move_order[disks_played][move_index] !=
best_list[best_list_index] )
move_index++;
}
else { /* Otherwise use information from shallow searches */
if ( !pre_search_done ) {
if ( remains < DEPTH_TWO_DEPTH )
pre_depth = 1;
else
pre_depth = 2;
pre_best = -INFINITE_EVAL;
empties_remaining = 60 - disks_played;
for ( move_index = 0; move_index < MOVE_ORDER_SIZE; move_index++ ) {
int already_checked;
move = sorted_move_order[disks_played][move_index];
already_checked = FALSE;
for ( j = 0; j < best_list_length; j++ )
if ( move == best_list[j] )
already_checked = TRUE;
if ( board[move] == EMPTY ) {
if ( !already_checked &&
(make_move( side_to_move, move, TRUE ) != 0 ) ) {
curr_val = -tree_search( level + 1, level + pre_depth,
OPP( side_to_move ), -INFINITE_EVAL,
-pre_best, FALSE, FALSE, TRUE );
pre_best = MAX( pre_best, curr_val );
unmake_move( side_to_move, move );
evals[disks_played][move] = curr_val;
feas_index_list[disks_played][move_count[disks_played]] =
move_index;
move_count[disks_played]++;
}
empties_remaining--;
if ( empties_remaining == 0 )
break;
}
}
pre_search_done = TRUE;
}
if ( i == move_count[disks_played] ) /* No moves left to try? */
break;
best_index = i;
best_score =
evals[disks_played][sorted_move_order[disks_played][feas_index_list[disks_played][i]]];
for ( j = i + 1; j < move_count[disks_played]; j++ ) {
int cand_move;
cand_move =
sorted_move_order[disks_played][feas_index_list[disks_played][j]];
if ( evals[disks_played][cand_move] > best_score ) {
best_score =
evals[disks_played][cand_move];
best_index = j;
}
}
move_index = feas_index_list[disks_played][best_index];
feas_index_list[disks_played][best_index] =
feas_index_list[disks_played][i];
}
move = sorted_move_order[disks_played][move_index];
counter_phase = (counter_phase + 1) & 63;
if ( counter_phase == 0 ) {
double node_val;
adjust_counter( &nodes );
node_val = counter_value( &nodes );
if ( node_val - last_panic_check >= EVENT_CHECK_INTERVAL ) {
/* Time abort? */
last_panic_check = node_val;
check_panic_abort();
/* Display available search information */
if ( echo )
display_buffers();
/* Check for events */
handle_event( TRUE, FALSE, TRUE );
if ( is_panic_abort() || force_return )
return SEARCH_ABORT;
}
}
(void) make_move( side_to_move, move, TRUE );
update_pv = FALSE;
if ( searched == 0 ) {
best = curr_val =
-tree_search( level + 1, max_depth, OPP( side_to_move ), -beta,
-curr_alpha, allow_hash, allow_mpc, TRUE );
best_move_index = move_index;
update_pv = TRUE;
}
else {
curr_alpha = MAX( best, curr_alpha );
curr_val =
-tree_search( level + 1, max_depth, OPP( side_to_move ),
-(curr_alpha + 1), -curr_alpha, allow_hash,
allow_mpc, TRUE );
if ( (curr_val > curr_alpha) && (curr_val < beta) ) {
curr_val =
-tree_search( level + 1, max_depth, OPP( side_to_move ), -beta,
INFINITE_EVAL, allow_hash, allow_mpc, TRUE );
if ( curr_val > best ) {
best = curr_val;
best_move_index = move_index;
update_pv = TRUE;
}
}
else if ( curr_val > best ) {
best = curr_val;
best_move_index = move_index;
update_pv = TRUE;
}
}
unmake_move( side_to_move, move );
if ( is_panic_abort() || force_return )
return SEARCH_ABORT;
evals[disks_played][move] = curr_val;
if ( update_pv ) {
update_best_list( best_list, move, best_list_index, best_list_length );
pv[level][level] = move;
pv_depth[level] = pv_depth[level + 1];
for ( j = level + 1; j < pv_depth[level + 1]; j++)
pv[level][j] = pv[level + 1][j];
}
if ( best >= beta ) {
advance_move( move_index );
if ( use_hash && allow_midgame_hash_update )
add_hash_extended( MIDGAME_MODE, best, best_list,
MIDGAME_SCORE | LOWER_BOUND, remains, selectivity );
return best;
}
searched++;
}
/* Post-processing */
#if CHECK_HASH_CODES && defined( TEXT_BASED )
if ( use_hash )
if ( (h1 != hash1) || (h2 != hash2) )
printf( "%s: %x%x %s: %x%x", HASH_BEFORE, h1, h2,
HASH_AFTER, hash1, hash2 );
#endif
if ( move_count[disks_played] > 0 ) {
advance_move( best_move_index );
if ( use_hash && allow_midgame_hash_update ) {
if ( best > alpha )
add_hash_extended( MIDGAME_MODE, best, best_list,
MIDGAME_SCORE | EXACT_VALUE, remains, selectivity );
else
add_hash_extended( MIDGAME_MODE, best, best_list,
MIDGAME_SCORE | UPPER_BOUND, remains, selectivity );
}
return best;
}
else if ( void_legal ) { /* No feasible moves */
hash1 ^= hash_flip_color1;
hash2 ^= hash_flip_color2;
curr_val = -tree_search( level, max_depth, OPP( side_to_move ), -beta,
-alpha, allow_hash, allow_mpc, FALSE );
hash1 ^= hash_flip_color1;
hash2 ^= hash_flip_color2;
return curr_val;
}
else {
pv_depth[level] = level;
return terminal_evaluation( side_to_move );
}
}
/*
PERTURB_SCORE
Perturbs SCORE by PERTURBATION if it doesn't appear to be
a midgame win.
*/
static int
perturb_score( int score, int perturbation ) {
if ( abs( score ) < ALMOST_MIDGAME_WIN )
return score + perturbation;
else
return score;
}
/*
ROOT_TREE_SEARCH
The recursive tree search function that is to be called only
for the root of the search tree.
*/
int
root_tree_search( int level, int max_depth, int side_to_move, int alpha,
int beta, int allow_hash, int allow_mpc, int void_legal ) {
char buffer[32];
int i, j;
int curr_val, best, pre_best;
int searched;
int move;
int move_index, best_move_index;
int hash_hit;
int pre_depth;
int update_pv;
int remains;
int use_hash, pre_search_done;
int curr_alpha;
int best_index, best_score;
int best_list_index, best_list_length;
int selectivity;
int offset;
int best_list[4];
HashEntry entry;
#if CHECK_HASH_CODES && defined( TEXT_BASED )
unsigned int h1, h2;
#endif
remains = max_depth - level;
INCREMENT_COUNTER( nodes );
use_hash = (remains >= HASH_THRESHOLD) && USE_HASH_TABLE && allow_hash;
if ( USE_MPC && allow_mpc )
selectivity = 1;
else
selectivity = 0;
#if CHECK_HASH_CODES && defined( TEXT_BASED )
if ( use_hash ) {
h1 = hash1;
h2 = hash2;
}
#endif
/* Hash strategy at the root: Only use hash table information for
move ordering purposes. This guarantees that score perturbation
is applied for all moves. */
hash_hit = FALSE;
if ( use_hash && allow_midgame_hash_probe ) {
find_hash( &entry, MIDGAME_MODE );
if ( entry.draft != NO_HASH_MOVE )
hash_hit = TRUE;
}
pre_search_done = FALSE;
if ( !get_ponder_move() ) {
if ( (alpha <= -MIDGAME_WIN) && (beta >= MIDGAME_WIN) )
sprintf( buffer, "[-inf,inf]:" );
else if ( (alpha <= -MIDGAME_WIN) && (beta < MIDGAME_WIN) )
sprintf( buffer, "[-inf,%.1f]:", beta / 128.0 );
else if ( (alpha > -MIDGAME_WIN) && (beta >= MIDGAME_WIN) )
sprintf( buffer, "[%.1f,inf]:", alpha / 128.0 );
else
sprintf( buffer, "[%.1f,%.1f]:", alpha / 128.0, beta / 128.0 );
clear_sweep();
send_sweep( "%-14s ", buffer );
}
/* Full negascout search */
searched = 0;
best = -INFINITE_EVAL;
best_move_index = -1,
curr_alpha = alpha;
best_list_length = 0;
for ( i = 0; i < 4; i++ )
best_list[i] = 0;
if ( !pre_search_done ) {
move_count[disks_played] = 0;
if ( hash_hit )
for ( i = 0; i < 4; i++ )
if ( valid_move( entry.move[i], side_to_move ) )
best_list[best_list_length++] = entry.move[i];
}
for ( i = 0, best_list_index = 0; TRUE; i++, best_list_index++ ) {
/* Try the hash table move(s) first if feasible */