tis 2022-07-05 klockan 22:26 +0200 skrev Andreas Rheinhardt: > From: Andreas Rheinhardt <andres.rheinha...@outlook.com> > > This is an array-equivalent of av_fast_realloc(). Its advantages > compared to using av_fast_realloc() for allocating arrays are as > follows: > > a) It performs its own overflow checks for the multiplication that is > implicit in array allocations. (And it only needs to perform these > checks (as well as the multiplication itself) in case the array needs > to > be reallocated.) > b) It allows to limit the number of elements to an upper bound given > by the caller. This allows to restrict the number of allocated > elements > to fit into an int and therefore makes this function usable with > counters of this type. It can also be used to avoid overflow checks > in > the caller: E.g. setting it to UINT_MAX - 1 elements makes it safe to > increase the desired number of elements in steps of one. And it > avoids > overallocations in situations where one already has an upper bound. > c) av_fast_realloc_array() will always allocate in multiples of array > elements; no memory is wasted with partial elements. > d) By returning an int, av_fast_realloc_array() can distinguish > between > ordinary allocation failures (meriting AVERROR(ENOMEM)) and failures > because of allocation limits (by returning AVERROR(ERANGE)). > e) It is no longer possible for the user to accidentally lose the > pointer by using ptr = av_fast_realloc(ptr, ...).
If you add an option for clearing the newly allocated memory then this could work for my av_fast_recalloc() use case in the jpeg2000 decoder. Or we could have two functions. Small bikeshed: since the function takes a pointer to a pointer as argument, av_fast_realloc_arrayp() might be a better name. I had in mind to similarly rename av_fast_recalloc() to av_fast_recallocp(). > + > + nb = min_nb + (min_nb + 14) / 16; Not +15? Or +0? > + > + /* If min_nb is so big that the above calculation overflowed, > + * just allocate as much as we are allowed to. */ > + nb = nb < min_nb ? max_nb : FFMIN(nb, max_nb); Looks OK, but an explicit check for overflow is easier to verify > + > + memcpy(&array, ptr, sizeof(array)); > + > + array = av_realloc(array, nb * elsize); > + if (!array) > + return AVERROR(ENOMEM); > + > + memcpy(ptr, &array, sizeof(array)); An optional memset() here would be useful for me Else it looks OK /Tomas _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
