1 files changed, 148 insertions, 0 deletions
diff --git a/src/evalhash.c b/src/evalhash.c
new file mode 100644
index 0000000..e0bc75e
--- /dev/null
+++ b/src/evalhash.c
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+/*++
+
+Copyright (c) Scott Gasch
+
+Module Name:
+
+    evalhash.c
+
+Abstract:
+
+    Evaluation score hashing code.
+
+Author:
+
+    Scott Gasch ([email protected]) 11 Jul 2006
+
+Revision History:
+
+--*/
+
+#include "chess.h"
+#ifdef EVAL_HASH
+
+extern ULONG g_uIterateDepth;
+
+SCORE 
+GetRoughEvalScore(IN OUT SEARCHER_THREAD_CONTEXT *ctx, 
+                  IN SCORE iAlpha,
+                  IN SCORE iBeta,
+                  IN FLAG fUseHash)
+/*++
+
+Routine description:
+
+    This is meant to be the "one place" that code looks when it needs to
+    get an idea of the estimated evaluation of a position (in mid tree,
+    not at the leaves... at the leaves just call Eval directly).
+    
+    The thought is that:
+    
+    1. The top of the tree (near the root) represents very few nodes
+    which have big subtrees.  Use the real Eval here.
+    
+    2. Otherwise possibly probe the eval hash -- if there's a score in
+    it then we can return quickly.
+    
+    3. Otherwise do a (very) rough material estimate.
+
+Parameters:
+
+    IN OUT SEARCHER_THREAD_CONTEXT *ctx,
+    IN SCORE iAlpha,
+    IN SCORE iBeta,
+    IN FLAG fUseHash
+
+Return value:
+
+    SCORE
+
+--*/
+{
+    POSITION *pos = &(ctx->sPosition);
+    UINT64 u64Key;
+    ULONG u;
+
+    if (ctx->uPly <= 4)
+    {
+        return Eval(ctx, iAlpha, iBeta);
+    }
+    else if ((fUseHash) || (ctx->uPly <= (g_uIterateDepth / 2)))
+    {
+        u64Key = (pos->u64PawnSig ^ pos->u64NonPawnSig);
+        u = (ULONG)u64Key & (EVAL_HASH_TABLE_SIZE - 1);
+        if (ctx->rgEvalHash[u].u64Key == u64Key)
+        {
+            ctx->uPositional = ctx->rgEvalHash[u].uPositional;
+            return(ctx->rgEvalHash[u].iEval);
+        }
+    }
+    return(pos->iMaterialBalance[pos->uToMove] + ctx->uPositional);
+}
+
+
+SCORE 
+ProbeEvalHash(IN OUT SEARCHER_THREAD_CONTEXT *ctx)
+/*++
+
+Routine description:
+
+    Probe the eval hash; return a real score if there's a hit
+    otherwise return INVALID_SCORE.
+
+Parameters:
+
+    IN OUT SEARCHER_THREAD_CONTEXT *ctx : note that in the case
+        of a hit, *ctx is modified also.
+
+Return value:
+
+    SCORE
+
+--*/
+{
+    POSITION *pos = &(ctx->sPosition);
+    UINT64 u64Key = (pos->u64PawnSig ^ pos->u64NonPawnSig);
+    ULONG u = (ULONG)u64Key & (EVAL_HASH_TABLE_SIZE - 1);
+
+    if (ctx->rgEvalHash[u].u64Key == u64Key)
+    {
+        ctx->uPositional = ctx->rgEvalHash[u].uPositional;
+        pos->cTrapped[WHITE] = ctx->rgEvalHash[u].cTrapped[WHITE];
+        pos->cTrapped[BLACK] = ctx->rgEvalHash[u].cTrapped[BLACK];
+        return(ctx->rgEvalHash[u].iEval);
+    }
+    return(INVALID_SCORE);
+}
+
+void 
+StoreEvalHash(IN OUT SEARCHER_THREAD_CONTEXT *ctx, 
+              IN SCORE iScore)
+/*++
+
+Routine description:
+
+    Store a score in the eval hash table (which is pointed to
+    indirectly via ctx).
+
+Parameters:
+
+    SEARCHER_THREAD_CONTEXT *ctx,
+    SCORE iScore
+
+Return value:
+
+    void
+
+--*/
+{
+    POSITION *pos = &(ctx->sPosition);
+    UINT64 u64Key = (pos->u64PawnSig ^ pos->u64NonPawnSig);
+    ULONG u = (ULONG)u64Key & (EVAL_HASH_TABLE_SIZE - 1);
+    ctx->rgEvalHash[u].u64Key = u64Key;
+    ctx->rgEvalHash[u].iEval = iScore;
+    ctx->rgEvalHash[u].uPositional = ctx->uPositional;
+    ctx->rgEvalHash[u].cTrapped[WHITE] = pos->cTrapped[WHITE];
+    ctx->rgEvalHash[u].cTrapped[BLACK] = pos->cTrapped[BLACK];
+}
+#endif // EVAL_HASH