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Better document how mate scores are stored in TT

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During the search we score a mate as "plies to mate
from the root" to compare in an homogeneous way the
values returned by different sub-trees. However we
store in TT a mate score as "plies to mate from the
current position" the let the TT value remain valid
across the game.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2011-12-28 13:22:09 +01:00
parent ad4739a6d4
commit 24417a6cd9
1 changed files with 6 additions and 5 deletions
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11
src/search.cpp
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@ -1370,7 +1370,7 @@ split_point_start: // At split points actual search starts from here
// All legal moves have been searched. A special case: If we're in check
// and no legal moves were found, it is checkmate.
if (inCheck && bestValue == -VALUE_INFINITE)
return mated_in(ss->ply);
return mated_in(ss->ply); // Plies to mate from the root
// Update transposition table
move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
@ -1495,8 +1495,8 @@ split_point_start: // At split points actual search starts from here
// value_to_tt() adjusts a mate score from "plies to mate from the root" to
// "plies to mate from the current ply". Non-mate scores are unchanged. The
// function is called before storing a value to the transposition table.
// "plies to mate from the current position". Non-mate scores are unchanged.
// The function is called before storing a value to the transposition table.
Value value_to_tt(Value v, int ply) {
@ -1510,8 +1510,9 @@ split_point_start: // At split points actual search starts from here
}
// value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
// the transposition table to a mate score corrected for the current ply.
// value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
// from the transposition table (where refers to the plies to mate/be mated
// from current position) to "plies to mate/be mated from the root".
Value value_from_tt(Value v, int ply) {