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While glibc provides qsort(), which usually is just a mergesort, until sorting arrays so huge that temporary array used by mergesort would not fit into physical memory (which in our case is never), we are not guaranteed it'll use mergesort. The advantage of mergesort is clear - it's stable. IOW, if we have an array of values parsed from XML, qsort() it and produce some output based on those values, we can then compare the output with some expected output, line by line. But with newer glibc this is all history. After [1], qsort() is no longer mergesort but introsort instead, which is not stable. This is suboptimal, because in some cases we want to preserve order of equal items. For instance, in ebiptablesApplyNewRules(), nwfilter rules are sorted by their priority. But if two rules have the same priority, we want to keep them in the order they appear in the XML. Since it's hard/needless work to identify places where stable or unstable sorting is needed, let's just play it safe and use stable sorting everywhere. Fortunately, glib provides g_qsort_with_data() which indeed implement mergesort and it's a drop in replacement for qsort(), almost. It accepts fifth argument (pointer to opaque data), that is passed to comparator function, which then accepts three arguments. We have to keep one occurance of qsort() though - in NSS module which deliberately does not link with glib. 1: https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=03bf8357e8291857a435afcc3048e0b697b6cc04 Signed-off-by: Michal Privoznik <mprivozn@redhat.com> Reviewed-by: Martin Kletzander <mkletzan@redhat.com> |
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