From: Florian Weimer Date: Wed, 8 Nov 2023 14:18:02 +0000 (+0100) Subject: stdlib: Avoid element self-comparisons in qsort X-Git-Tag: glibc-2.39~299 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f8cfb6836e8d91bb789b2e7fd65338d6f5bd459c;p=thirdparty%2Fglibc.git stdlib: Avoid element self-comparisons in qsort This improves compatibility with applications which assume that qsort does not invoke the comparison function with equal pointer arguments. The newly introduced branches should be predictable, as leading to a call to the comparison function. If the prediction fails, we avoid calling the function. Reviewed-by: Adhemerval Zanella --- diff --git a/stdlib/qsort.c b/stdlib/qsort.c index fd32a165e73..ad110e8a892 100644 --- a/stdlib/qsort.c +++ b/stdlib/qsort.c @@ -136,7 +136,7 @@ siftdown (void *base, size_t size, size_t k, size_t n, if (j < n && cmp (base + (j * size), base + ((j + 1) * size), arg) < 0) j++; - if (cmp (base + (k * size), base + (j * size), arg) >= 0) + if (j == k || cmp (base + (k * size), base + (j * size), arg) >= 0) break; do_swap (base + (size * j), base + (k * size), size, swap_type); @@ -332,10 +332,12 @@ __qsort_r (void *const pbase, size_t total_elems, size_t size, that this algorithm runs much faster than others. */ do { - while ((*cmp) ((void *) left_ptr, (void *) mid, arg) < 0) + while (left_ptr != mid + && (*cmp) ((void *) left_ptr, (void *) mid, arg) < 0) left_ptr += size; - while ((*cmp) ((void *) mid, (void *) right_ptr, arg) < 0) + while (right_ptr != mid + && (*cmp) ((void *) mid, (void *) right_ptr, arg) < 0) right_ptr -= size; if (left_ptr < right_ptr)