ons 2022-07-06 klockan 16:46 +0200 skrev Andreas Rheinhardt: > Tomas Härdin: > > 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. > > > > I'd prefer it if the zeroing function were a wrapper around the > non-zeroing function.
That should work, the change in allocated entries can be detected > > > 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? > > "av_fast_realloc_array() instead allocates nb + (nb + 14) / 16. > Rounding > up is done in order not to reallocate in steps of one if the current > number is < 16; adding 14 instead of 15 has the effect of only > allocating one element if one element is desired." Wups, I actually read that part of the commit message then forgot about it. I blame sickness /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".
