Fix end-of-loop optimization in pglz_find_match() function.

hlinnaka · hlinnaka · commit 3f2adace1ec0 · 2013-07-17T20:37:09.000+03:00
After the recent pglz optimization patch, the next/prev pointers in the
hash table are never NULL, INVALID_ENTRY_PTR is used to represent invalid
entries instead. The end-of-loop check in pglz_find_match() function didn't
get the memo. The result was the same from a correctness point of view, but
because the NULL-check would never fail, the tiny optimization turned into
a pessimization.

Reported by Stephen Frost, using Coverity scanner.
diff --git a/src/backend/utils/adt/pg_lzcompress.c b/src/backend/utils/adt/pg_lzcompress.c
@@ -466,7 +466,7 @@ pglz_find_match(int16 *hstart, const char *input, const char *end,
 		 * Be happy with lesser good matches the more entries we visited. But
 		 * no point in doing calculation if we're at end of list.
 		 */
-		if (hent)
+		if (hent != INVALID_ENTRY_PTR)
 		{
 			if (len >= good_match)
 				break;

Original file line number	Diff line number	Diff line change
`@@ -466,7 +466,7 @@ pglz_find_match(int16 hstart, const char input, const char *end,`
`466`	`466`	`* Be happy with lesser good matches the more entries we visited. But`
`467`	`467`	`* no point in doing calculation if we're at end of list.`
`468`	`468`	`*/`
`469`		`- if (hent)`
	`469`	`+ if (hent != INVALID_ENTRY_PTR)`
`470`	`470`	`{`
`471`	`471`	`if (len >= good_match)`
`472`	`472`	`break;`