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Skip memcpy(x, x) in qunique().

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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
This commit is contained in:
Noah Misch 2020-01-04 11:31:42 -08:00
parent fac1c04fec
commit 5b630501e9
1 changed files with 6 additions and 4 deletions
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10
src/include/lib/qunique.h
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@ -30,8 +30,9 @@ qunique(void *array, size_t elements, size_t width,
for (i = 1, j = 0; i < elements; ++i) for (i = 1, j = 0; i < elements; ++i)
{ {
if (compare(bytes + i * width, bytes + j * width) != 0) if (compare(bytes + i * width, bytes + j * width) != 0 &&
memcpy(bytes + ++j * width, bytes + i * width, width); ++j != i)
memcpy(bytes + j * width, bytes + i * width, width);
} }
return j + 1; 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) for (i = 1, j = 0; i < elements; ++i)
{ {
if (compare(bytes + i * width, bytes + j * width, arg) != 0) if (compare(bytes + i * width, bytes + j * width, arg) != 0 &&
memcpy(bytes + ++j * width, bytes + i * width, width); ++j != i)
memcpy(bytes + j * width, bytes + i * width, width);
} }
return j + 1; return j + 1;