On Wed, Jun 28, 2023 at 12:26 AM Andreas Rheinhardt <
andreas.rheinha...@outlook.com> wrote:
> Paul B Mahol:
> > On Tue, Jun 27, 2023 at 11:45 PM Andreas Rheinhardt <
> > andreas.rheinha...@outlook.com> wrote:
> >
> >> Paul B Mahol:
> >>> On Tue, Jun 27, 2023 at 11:05 PM Andreas Rheinhardt <
> >>> andreas.rheinha...@outlook.com> wrote:
> >>>
> >>>> Paul B Mahol:
> >>>>> On Tue, Jun 27, 2023 at 9:47 PM Andreas Rheinhardt <
> >>>>> andreas.rheinha...@outlook.com> wrote:
> >>>>>
> >>>>>> Paul B Mahol:
> >>>>>>> Patch attached.
> >>>>>>>
> >>>>>>
> >>>>>> Where do you intend to use this? What is the point of it?
> >>>>>> After all, using this value in GET_VLC makes no sense; only
> >> compile-time
> >>>>>> constants do.
> >>>>>>
> >>>>>
> >>>>> It works when used in ac-4 as get_vlc2.
> >>>>>
> >>>>
> >>>> Could you please define "works"? Using a non-compile-time constant
> will
> >>>> not benefit at all; it will only lead to more runtime checks.
> >>>>
> >>>
> >>> I do not follow your worries.
> >>> I can not use compile time constant as its very complicated code.
> >>>
> >>
> >> Let's take a look at GET_VLC:
> >> #define GET_VLC(code, name, gb, table, bits, max_depth) \
> >> do { \
> >> int n, nb_bits; \
> >> unsigned int index; \
> >> \
> >> index = SHOW_UBITS(name, gb, bits); \
> >> code = table[index].sym; \
> >> n = table[index].len; \
> >> \
> >> if (max_depth > 1 && n < 0) { \
> >> LAST_SKIP_BITS(name, gb, bits); \
> >> UPDATE_CACHE(name, gb); \
> >> \
> >> nb_bits = -n; \
> >> \
> >> index = SHOW_UBITS(name, gb, nb_bits) + code; \
> >> code = table[index].sym; \
> >> n = table[index].len; \
> >> if (max_depth > 2 && n < 0) { \
> >> LAST_SKIP_BITS(name, gb, nb_bits); \
> >> UPDATE_CACHE(name, gb); \
> >> \
> >> nb_bits = -n; \
> >> \
> >> index = SHOW_UBITS(name, gb, nb_bits) + code; \
> >> code = table[index].sym; \
> >> n = table[index].len; \
> >> } \
> >> } \
> >> SKIP_BITS(name, gb, n); \
> >> } while (0)
> >>
> >> If max_depth is not a compile-time constant, then the compiler will have
> >> to perform both of the max_depth > 1 && n < 0 checks; yet, this is not
> >> useful: If the depth of a particular VLC is (say) 1, then none of the
> >> possible bits read will lead to reloading at all, because the n < 0
> >> condition will never be true; the only reason this condition exists is
> >> to use a compile-time upper bound, so that one can eliminate the reload
> >> code (and in particular, avoid the runtime checks).
> >>
> >>> Works means that vlc code is extracted correctly.
> >>>
> >>
> >> If you have no upper bound about max_depth and it works, then use 3.
> >>
> >
> > It does not work to use 3 all the time. And that one never worked in any
> > codec so far.
> >
>
> I just ran FATE with the check for max_depth removed from GET_VLC and
> from read_vlc for the cached API (effectively setting max_depth to 3
> everywhere). It passed. So it "works" (but in a suboptimal way). At
> least it does if you have ordinary VLCs (created by the vlc.c
> functions). Are you doing anything special with them or so?
>
FATE code coverage is very limited.
Also I do not follow your reasoning about this added field at all.
What is calculated over and over again in each get_vlc2() call?
>
> - Andreas
>
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