Modify additional power 2 calculations to use new helper functions

david-rowley · david-rowley · commit 02a2e8b44200 · 2020-04-08T18:29:51.000+12:00
2nd pass of modifying various places which obtain the next power of 2 of a number and make them use the new functions added in f0705bb. In passing, also modify num_combinations(). This can be implemented using simple bitshifting rather than looping. Reviewed-by: John Naylor Discussion: https://postgr.es/m/20200114173553.GE32763%40fetter.org
diff --git a/src/backend/access/gin/ginfast.c b/src/backend/access/gin/ginfast.c
@@ -25,6 +25,7 @@
 #include "catalog/pg_am.h"
 #include "commands/vacuum.h"
 #include "miscadmin.h"
+#include "port/pg_bitutils.h"
 #include "postmaster/autovacuum.h"
 #include "storage/indexfsm.h"
 #include "storage/lmgr.h"
@@ -503,10 +504,7 @@ ginHeapTupleFastCollect(GinState *ginstate,
 		 * initially.  Make it a power of 2 to avoid wasting memory when
 		 * resizing (since palloc likes powers of 2).
 		 */
-		collector->lentuples = 16;
-		while (collector->lentuples < nentries)
-			collector->lentuples *= 2;
-
+		collector->lentuples = pg_nextpower2_32(Max(16, nentries));
 		collector->tuples = (IndexTuple *) palloc(sizeof(IndexTuple) * collector->lentuples);
 	}
 	else if (collector->lentuples < collector->ntuples + nentries)
@@ -516,11 +514,7 @@ ginHeapTupleFastCollect(GinState *ginstate,
 		 * overflow, though we could get to a value that exceeds
 		 * MaxAllocSize/sizeof(IndexTuple), causing an error in repalloc.
 		 */
-		do
-		{
-			collector->lentuples *= 2;
-		} while (collector->lentuples < collector->ntuples + nentries);
-
+		collector->lentuples = pg_nextpower2_32(collector->ntuples + nentries);
 		collector->tuples = (IndexTuple *) repalloc(collector->tuples,
 													sizeof(IndexTuple) * collector->lentuples);
 	}
diff --git a/src/backend/executor/nodeHash.c b/src/backend/executor/nodeHash.c
@@ -831,9 +831,7 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew,
 		dbatch = ceil(inner_rel_bytes / (hash_table_bytes - bucket_bytes));
 		dbatch = Min(dbatch, max_pointers);
 		minbatch = (int) dbatch;
-		nbatch = 2;
-		while (nbatch < minbatch)
-			nbatch <<= 1;
+		nbatch = pg_nextpower2_32(Max(2, minbatch));
 	}
 
 	Assert(nbuckets > 0);
@@ -2272,9 +2270,7 @@ ExecHashBuildSkewHash(HashJoinTable hashtable, Hash *node, int mcvsToUse)
 		 * MaxAllocSize/sizeof(void *)/8, but that is not currently possible
 		 * since we limit pg_statistic entries to much less than that.
 		 */
-		nbuckets = 2;
-		while (nbuckets <= mcvsToUse)
-			nbuckets <<= 1;
+		nbuckets = pg_nextpower2_32(mcvsToUse + 1);
 		/* use two more bits just to help avoid collisions */
 		nbuckets <<= 2;
 
diff --git a/src/backend/nodes/list.c b/src/backend/nodes/list.c
@@ -18,6 +18,7 @@
 #include "postgres.h"
 
 #include "nodes/pg_list.h"
+#include "port/pg_bitutils.h"
 #include "utils/memdebug.h"
 #include "utils/memutils.h"
 
@@ -119,9 +120,7 @@ new_list(NodeTag type, int min_size)
 	 * that's more than twice the size of an existing list, so the size limits
 	 * within palloc will ensure that we don't overflow here.
 	 */
-	max_size = 8;				/* semi-arbitrary small power of 2 */
-	while (max_size < min_size + LIST_HEADER_OVERHEAD)
-		max_size *= 2;
+	max_size = pg_nextpower2_32(Max(8, min_size + LIST_HEADER_OVERHEAD));
 	max_size -= LIST_HEADER_OVERHEAD;
 #else
 
@@ -160,12 +159,12 @@ enlarge_list(List *list, int min_size)
 
 	/*
 	 * As above, we prefer power-of-two total allocations; but here we need
-	 * not account for list header overhead.  The existing max length might
-	 * not be a power of 2, so don't rely on that.
+	 * not account for list header overhead.
 	 */
-	new_max_len = 16;			/* semi-arbitrary small power of 2 */
-	while (new_max_len < min_size)
-		new_max_len *= 2;
+
+	/* clamp the minimum value to 16, a semi-arbitrary small power of 2 */
+	new_max_len = pg_nextpower2_32(Max(16, min_size));
+
 #else
 	/* As above, don't allocate anything extra */
 	new_max_len = min_size;
diff --git a/src/backend/statistics/mvdistinct.c b/src/backend/statistics/mvdistinct.c
@@ -576,15 +576,7 @@ n_choose_k(int n, int k)
 static int
 num_combinations(int n)
 {
-	int			k;
-	int			ncombs = 1;
-
-	for (k = 1; k <= n; k++)
-		ncombs *= 2;
-
-	ncombs -= (n + 1);
-
-	return ncombs;
+	return (1 << n) - (n + 1);
 }
 
 /*
diff --git a/src/backend/utils/adt/arrayfuncs.c b/src/backend/utils/adt/arrayfuncs.c
@@ -24,6 +24,7 @@
 #include "nodes/nodeFuncs.h"
 #include "nodes/supportnodes.h"
 #include "optimizer/optimizer.h"
+#include "port/pg_bitutils.h"
 #include "utils/array.h"
 #include "utils/arrayaccess.h"
 #include "utils/builtins.h"
@@ -5313,9 +5314,7 @@ accumArrayResultArr(ArrayBuildStateArr *astate,
 		memcpy(&astate->lbs[1], lbs, ndims * sizeof(int));
 
 		/* Allocate at least enough data space for this item */
-		astate->abytes = 1024;
-		while (astate->abytes <= ndatabytes)
-			astate->abytes *= 2;
+		astate->abytes = pg_nextpower2_32(Max(1024, ndatabytes + 1));
 		astate->data = (char *) palloc(astate->abytes);
 	}
 	else
@@ -5362,9 +5361,7 @@ accumArrayResultArr(ArrayBuildStateArr *astate,
 			 * First input with nulls; we must retrospectively handle any
 			 * previous inputs by marking all their items non-null.
 			 */
-			astate->aitems = 256;
-			while (astate->aitems <= newnitems)
-				astate->aitems *= 2;
+			astate->aitems = pg_nextpower2_32(Max(256, newnitems + 1));
 			astate->nullbitmap = (bits8 *) palloc((astate->aitems + 7) / 8);
 			array_bitmap_copy(astate->nullbitmap, 0,
 							  NULL, 0,
