postgres.git / summary / log / commit / refs

commit    5b630501e9fa58c5069b36247d63fc460d912c7f
Author:   Noah Misch <noah@leadboat.com>
Date:     Sat Jan 04 19:31:42 2020 +0000
First released in: 13.0

    Skip memcpy(x, x) in qunique().
    
    It has undefined behavior.  Follow the precedent of commit
    9a9473f3cce1a21c25d6cc7569710e832d2b180b.  No back-patch, since the
    master branch alone has this function.
    
    Discussion: https://postgr.es/m/20191229070221.GA13873@gust.leadboat.com


 src/include/lib/qunique.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/include/lib/qunique.h b/src/include/lib/qunique.h
index 73aa10f1659..95d9fef637a 100644
--- a/src/include/lib/qunique.h
+++ b/src/include/lib/qunique.h
@@ -30,8 +30,9 @@ qunique(void *array, size_t elements, size_t width,
 
 	for (i = 1, j = 0; i < elements; ++i)
 	{
-		if (compare(bytes + i * width, bytes + j * width) != 0)
-			memcpy(bytes + ++j * width, bytes + i * width, width);
+		if (compare(bytes + i * width, bytes + j * width) != 0 &&
+			++j != i)
+			memcpy(bytes + j * width, bytes + i * width, width);
 	}
 
 	return j + 1;
@@ -55,8 +56,9 @@ qunique_arg(void *array, size_t elements, size_t width,
 
 	for (i = 1, j = 0; i < elements; ++i)
 	{
-		if (compare(bytes + i * width, bytes + j * width, arg) != 0)
-			memcpy(bytes + ++j * width, bytes + i * width, width);
+		if (compare(bytes + i * width, bytes + j * width, arg) != 0 &&
+			++j != i)
+			memcpy(bytes + j * width, bytes + i * width, width);
 	}
 
 	return j + 1;


[parent: fac1c04feca6]