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diff --git a/src/backend/access/gin/ginlogic.c b/src/backend/access/gin/ginlogic.c
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+/*-------------------------------------------------------------------------
+ *
+ * ginlogic.c
+ *	  routines for performing binary- and ternary-logic consistent checks.
+ *
+ * A GIN operator class can provide a boolean or ternary consistent
+ * function, or both.  This file provides both boolean and ternary
+ * interfaces to the rest of the GIN code, even if only one of them is
+ * implemented by the opclass.
+ *
+ * Providing a boolean interface when the opclass implements only the
+ * ternary function is straightforward - just call the ternary function
+ * with the check-array as is, and map the GIN_TRUE, GIN_FALSE, GIN_MAYBE
+ * return codes to TRUE, FALSE and TRUE+recheck, respectively.  Providing
+ * a ternary interface when the opclass only implements a boolean function
+ * is implemented by calling the boolean function many times, with all the
+ * MAYBE arguments set to all combinations of TRUE and FALSE (up to a
+ * certain number of MAYBE arguments).
+ *
+ * (A boolean function is enough to determine if an item matches, but a
+ * GIN scan can apply various optimizations if it can determine that an
+ * item matches or doesn't match, even if it doesn't know if some of the
+ * keys are present or not.  That's what the ternary consistent function
+ * is used for.)
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *			src/backend/access/gin/ginlogic.c
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/gin_private.h"
+#include "access/reloptions.h"
+#include "catalog/pg_collation.h"
+#include "catalog/pg_type.h"
+#include "miscadmin.h"
+#include "storage/indexfsm.h"
+#include "storage/lmgr.h"
+
+
+/*
+ * Maximum number of MAYBE inputs that shimTriConsistentFn will try to
+ * resolve by calling all combinations.
+ */
+#define MAX_MAYBE_ENTRIES	4
+
+/*
+ * Dummy consistent functions for an EVERYTHING key.  Just claim it matches.
+ */
+static bool
+trueConsistentFn(GinScanKey key)
+{
+	key->recheckCurItem = false;
+	return true;
+}
+static GinTernaryValue
+trueTriConsistentFn(GinScanKey key)
+{
+	return GIN_TRUE;
+}
+
+/*
+ * A helper function for calling a regular, binary logic, consistent function.
+ */
+static bool
+directBoolConsistentFn(GinScanKey key)
+{
+	/*
+	 * Initialize recheckCurItem in case the consistentFn doesn't know it
+	 * should set it.  The safe assumption in that case is to force recheck.
+	 */
+	key->recheckCurItem = true;
+
+	return DatumGetBool(FunctionCall8Coll(key->consistentFmgrInfo,
+										  key->collation,
+										  PointerGetDatum(key->entryRes),
+										  UInt16GetDatum(key->strategy),
+										  key->query,
+										  UInt32GetDatum(key->nuserentries),
+										  PointerGetDatum(key->extra_data),
+										  PointerGetDatum(&key->recheckCurItem),
+										  PointerGetDatum(key->queryValues),
+										  PointerGetDatum(key->queryCategories)));
+}
+
+/*
+ * A helper function for calling a native ternary logic consistent function.
+ */
+static GinTernaryValue
+directTriConsistentFn(GinScanKey key)
+{
+	return DatumGetGinTernaryValue(FunctionCall7Coll(key->triConsistentFmgrInfo,
+													 key->collation,
+													 PointerGetDatum(key->entryRes),
+													 UInt16GetDatum(key->strategy),
+													 key->query,
+													 UInt32GetDatum(key->nuserentries),
+													 PointerGetDatum(key->extra_data),
+													 PointerGetDatum(key->queryValues),
+													 PointerGetDatum(key->queryCategories)));
+}
+
+/*
+ * This function implements a binary logic consistency check, using a ternary
+ * logic consistent function provided by the opclass. GIN_MAYBE return value
+ * is interpreted as true with recheck flag.
+ */
+static bool
+shimBoolConsistentFn(GinScanKey key)
+{
+	GinTernaryValue result;
+
+	result = DatumGetGinTernaryValue(FunctionCall7Coll(key->triConsistentFmgrInfo,
+													   key->collation,
+													   PointerGetDatum(key->entryRes),
+													   UInt16GetDatum(key->strategy),
+													   key->query,
+													   UInt32GetDatum(key->nuserentries),
+													   PointerGetDatum(key->extra_data),
+													   PointerGetDatum(key->queryValues),
+													   PointerGetDatum(key->queryCategories)));
+	if (result == GIN_MAYBE)
+	{
+		key->recheckCurItem = true;
+		return true;
+	}
+	else
+	{
+		key->recheckCurItem = false;
+		return result;
+	}
+}
+
+/*
+ * This function implements a tri-state consistency check, using a boolean
+ * consistent function provided by the opclass.
+ *
+ * Our strategy is to call consistentFn with MAYBE inputs replaced with every
+ * combination of TRUE/FALSE. If consistentFn returns the same value for every
+ * combination, that's the overall result. Otherwise, return MAYBE. Testing
+ * every combination is O(n^2), so this is only feasible for a small number of
+ * MAYBE inputs.
+ *
+ * NB: This function modifies the key->entryRes array!
+ */
+static GinTernaryValue
+shimTriConsistentFn(GinScanKey key)
+{
+	int			nmaybe;
+	int			maybeEntries[MAX_MAYBE_ENTRIES];
+	int			i;
+	bool		boolResult;
+	bool		recheck = false;
+	GinTernaryValue curResult;
+
+	/*
+	 * Count how many MAYBE inputs there are, and store their indexes in
+	 * maybeEntries. If there are too many MAYBE inputs, it's not feasible to
+	 * test all combinations, so give up and return MAYBE.
+	 */
+	nmaybe = 0;
+	for (i = 0; i < key->nentries; i++)
+	{
+		if (key->entryRes[i] == GIN_MAYBE)
+		{
+			if (nmaybe >= MAX_MAYBE_ENTRIES)
+				return GIN_MAYBE;
+			maybeEntries[nmaybe++] = i;
+		}
+	}
+
+	/*
+	 * If none of the inputs were MAYBE, so we can just call consistent
+	 * function as is.
+	 */
+	if (nmaybe == 0)
+		return directBoolConsistentFn(key);
+
+	/* First call consistent function with all the maybe-inputs set FALSE */
+	for (i = 0; i < nmaybe; i++)
+		key->entryRes[maybeEntries[i]] = GIN_FALSE;
+	curResult = directBoolConsistentFn(key);
+
+	for (;;)
+	{
+		/* Twiddle the entries for next combination. */
+		for (i = 0; i < nmaybe; i++)
+		{
+			if (key->entryRes[maybeEntries[i]] == GIN_FALSE)
+			{
+				key->entryRes[maybeEntries[i]] = GIN_TRUE;
+				break;
+			}
+			else
+				key->entryRes[maybeEntries[i]] = GIN_FALSE;
+		}
+		if (i == nmaybe)
+			break;
+
+		boolResult = directBoolConsistentFn(key);
+		recheck |= key->recheckCurItem;
+
+		if (curResult != boolResult)
+			return GIN_MAYBE;
+	}
+
+	/* TRUE with recheck is taken to mean MAYBE */
+	if (curResult == GIN_TRUE && recheck)
+		curResult = GIN_MAYBE;
+
+	return curResult;
+}
+
+/*
+ * Set up the implementation of the consistent functions for a scan key.
+ */
+void
+ginInitConsistentFunction(GinState *ginstate, GinScanKey key)
+{
+	if (key->searchMode == GIN_SEARCH_MODE_EVERYTHING)
+	{
+		key->boolConsistentFn = trueConsistentFn;
+		key->triConsistentFn = trueTriConsistentFn;
+	}
+	else
+	{
+		key->consistentFmgrInfo = &ginstate->consistentFn[key->attnum - 1];
+		key->triConsistentFmgrInfo = &ginstate->triConsistentFn[key->attnum - 1];
+		key->collation = ginstate->supportCollation[key->attnum - 1];
+
+		if (OidIsValid(ginstate->consistentFn[key->attnum - 1].fn_oid))
+			key->boolConsistentFn = directBoolConsistentFn;
+		else
+			key->boolConsistentFn = shimBoolConsistentFn;
+
+		if (OidIsValid(ginstate->triConsistentFn[key->attnum - 1].fn_oid))
+			key->triConsistentFn = directTriConsistentFn;
+		else
+			key->triConsistentFn = shimTriConsistentFn;
+	}
+}