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Code Issues Releases Wiki Activity

Document probe_ab()

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This commit is contained in:
Marco Costalba 2016-05-19 11:41:09 +02:00
parent b465f2b44a
commit 7dc41c7929
1 changed files with 21 additions and 9 deletions
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30
src/syzygy/tbprobe.cpp
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@ -1219,7 +1219,16 @@ ExtMove *add_underprom_caps(Position& pos, ExtMove *stack, ExtMove *end)
return extra; return extra;
} }
WDLScore probe_ab(Position& pos, WDLScore alpha, WDLScore beta, int *success) // For a position where the side to move has a winning capture it is not necessary
// to store a winning value so the generator treats such positions as "don't cares"
// and tries to assign to it a value that improves the compression ratio. Similarly,
// if the side to move has a drawing capture, then the position is at least drawn.
// If the position is won, then the TB needs to store a win value. But if the
// position is drawn, the TB may store a loss value if that is better for compression.
// All of this means that during probing, the engine must look at captures and probe
// their results and must probe the position itself. The "best" result of these
// probes is the correct result for the position.
WDLScore search(Position& pos, WDLScore alpha, WDLScore beta, int *success)
{ {
WDLScore value; WDLScore value;
ExtMove stack[64]; ExtMove stack[64];
@ -1237,6 +1246,8 @@ WDLScore probe_ab(Position& pos, WDLScore alpha, WDLScore beta, int *success)
CheckInfo ci(pos); CheckInfo ci(pos);
// Search caputures first accessing smaller tb tables, that potentially are
// easier to be RAM cached.
for (moves = stack; moves < end; ++moves) { for (moves = stack; moves < end; ++moves) {
Move capture = moves->move; Move capture = moves->move;
@ -1246,7 +1257,7 @@ WDLScore probe_ab(Position& pos, WDLScore alpha, WDLScore beta, int *success)
continue; continue;
pos.do_move(capture, st, pos.gives_check(capture, ci)); pos.do_move(capture, st, pos.gives_check(capture, ci));
value = -probe_ab(pos, -beta, -alpha, success); value = -search(pos, -beta, -alpha, success);
pos.undo_move(capture); pos.undo_move(capture);
if (*success == 0) if (*success == 0)
@ -1262,7 +1273,8 @@ WDLScore probe_ab(Position& pos, WDLScore alpha, WDLScore beta, int *success)
} }
} }
value = probe_wdl_table(pos, success); // FIXME why this is not at the beginning? // Then probe the position, accessing a bigger file table
value = probe_wdl_table(pos, success);
if (*success == 0) if (*success == 0)
return WDLDraw; return WDLDraw;
@ -1283,7 +1295,7 @@ int probe_dtz_no_ep(Position& pos, int *success)
{ {
int dtz; int dtz;
WDLScore wdl = probe_ab(pos, WDLLoss, WDLWin, success); WDLScore wdl = search(pos, WDLLoss, WDLWin, success);
if (!*success) if (!*success)
return 0; return 0;
@ -1316,7 +1328,7 @@ int probe_dtz_no_ep(Position& pos, int *success)
continue; continue;
pos.do_move(move, st, pos.gives_check(move, ci)); pos.do_move(move, st, pos.gives_check(move, ci));
WDLScore v = -probe_ab(pos, WDLLoss, -wdl + WDLCursedWin, success); WDLScore v = -search(pos, WDLLoss, -wdl + WDLCursedWin, success);
pos.undo_move(move); pos.undo_move(move);
if (*success == 0) return 0; if (*success == 0) return 0;
@ -1376,7 +1388,7 @@ int probe_dtz_no_ep(Position& pos, int *success)
if (st.rule50 == 0) { if (st.rule50 == 0) {
if (wdl == -2) v = -1; if (wdl == -2) v = -1;
else { else {
v = probe_ab(pos, WDLCursedWin, WDLWin, success); v = search(pos, WDLCursedWin, WDLWin, success);
v = (v == 2) ? 0 : -101; v = (v == 2) ? 0 : -101;
} }
} else { } else {
@ -1455,7 +1467,7 @@ int probe_dtz(Position& pos, int *success)
continue; continue;
pos.do_move(capture, st, pos.gives_check(capture, ci)); pos.do_move(capture, st, pos.gives_check(capture, ci));
WDLScore v0 = -probe_ab(pos, WDLLoss, WDLWin, success); WDLScore v0 = -search(pos, WDLLoss, WDLWin, success);
pos.undo_move(capture); pos.undo_move(capture);
if (*success == 0) if (*success == 0)
@ -1656,7 +1668,7 @@ void Tablebases::init(const std::string& paths)
WDLScore Tablebases::probe_wdl(Position& pos, int *success) WDLScore Tablebases::probe_wdl(Position& pos, int *success)
{ {
*success = 1; *success = 1;
WDLScore v = probe_ab(pos, WDLLoss, WDLWin, success); WDLScore v = search(pos, WDLLoss, WDLWin, success);
// If en passant is not possible, we are done. // If en passant is not possible, we are done.
if (pos.ep_square() == SQ_NONE) if (pos.ep_square() == SQ_NONE)
@ -1687,7 +1699,7 @@ WDLScore Tablebases::probe_wdl(Position& pos, int *success)
continue; continue;
pos.do_move(capture, st, pos.gives_check(capture, ci)); pos.do_move(capture, st, pos.gives_check(capture, ci));
WDLScore v0 = -probe_ab(pos, WDLLoss, WDLWin, success); WDLScore v0 = -search(pos, WDLLoss, WDLWin, success);
pos.undo_move(capture); pos.undo_move(capture);
if (*success == 0) if (*success == 0)