From 5b630501e9fa58c5069b36247d63fc460d912c7f Mon Sep 17 00:00:00 2001 From: Noah Misch Date: Sat, 4 Jan 2020 11:31:42 -0800 Subject: [PATCH] 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;