Hi, On Mon, Oct 12, 2015 at 7:12 AM, Ganesh Ajjanagadde <gajja...@mit.edu> wrote:
> On Mon, Oct 12, 2015 at 6:30 AM, Michael Niedermayer > <mich...@niedermayer.cc> wrote: > > On Sun, Oct 11, 2015 at 10:02:29PM -0400, Ronald S. Bultje wrote: > >> Hi, > >> > >> On Sun, Oct 11, 2015 at 9:17 PM, Ganesh Ajjanagadde <gajja...@mit.edu> > >> wrote: > >> > >> > On Sun, Oct 11, 2015 at 9:12 PM, Ganesh Ajjanagadde <gajja...@mit.edu > > > >> > wrote: > >> > > On Sun, Oct 11, 2015 at 6:04 PM, Ronald S. Bultje < > rsbul...@gmail.com> > >> > wrote: > >> > >> Hi, > >> > >> > >> > >> On Sun, Oct 11, 2015 at 5:52 PM, Andreas Cadhalpun < > >> > >> andreas.cadhal...@googlemail.com> wrote: > >> > >> > >> > >>> On 11.10.2015 23:44, Ronald S. Bultje wrote: > >> > >>> > It's a non-installed header and only used in one place > (flacenc). > >> > >>> > Since ff_ctz is static inline, it's fine to use that instead. > >> > >>> > --- > >> > >>> > doc/APIchanges | 3 --- > >> > >>> > libavcodec/flacenc.c | 2 +- > >> > >>> > libavutil/intmath.c | 5 ----- > >> > >>> > libavutil/intmath.h | 14 ++++++-------- > >> > >>> > 4 files changed, 7 insertions(+), 17 deletions(-) > >> > >>> > >> > >>> Should be fine. > >> > >> > >> > >> > >> > >> Thanks, pushed. > >> > > > >> > > Since there is still time, and I did not think of this before, I > would > >> > > like to replace ff_ctz with ff_ctz32. There are a couple of reasons: > >> > > 1. It is used with an int32 argument in flacenc. > >> > > 2. I can do a deBruijn optimization for this as well. With an int > also > >> > > I could do it, but it would need some ifdefry depending on whether > int > >> > > is 32 bit or 64 bits. > >> > > > >> > > Let me see if I understand API/ABI with respect to this proposed > >> > > change correctly now: > >> > > API is not broken, as this is not public. > >> > > ABI is broken, since the width of operands to ff_ctz has could > change > >> > > from 64 to 32 bits. > >> > > >> > That actually raises the question of whether int = 32 bits is assumed > >> > everywhere. For instance, if int = 64 bits, at least on the Intel > >> > compiler, ff_ctz is broken: AFAIK, _bit_scan_forward operates on 32 > >> > bit operands. > >> > >> > >> I think you can safely assume int is 32bit, we do so in numerous places. > > > > we assume int >= 32 bit all over (posix gurantees it) > > int == 32bit is assumed in some arch specific code like simd asm > > > > generic code should not assume int to be 32bit > > or rather IMHO we should not conciously add any such code as it just > > violates C and will break on some (currently) uncommon platforms/configs > > ff_ctz is currently not "generic", it is very much bit width specific. > For instance, ff_ctz_c is broken if int = 64 bit, _bit_scan_forward is > also broken if int = 64 bit. Thus, at least on ICC or non (MSC || GCC) > it is broken (even on MSC it is, there is a _BitScanForward64; but at > least Microsoft can dictate "int = 32"). By doing my proposed change, > at the very least we are explicit in what we do - we have ff_ctz32 for > 32 bits, ff_ctzll (I can rename this to ff_ctz64) force 64 bits. > Moreover, ff_ctz's only use in flacenc is with a int_32. I don't think we need ff_ctzll, since it would have no users. We typically add functions when they are used. Renaming ff_ctz to ff_ctz32 is OK with me, although I don't care much either way. Let's continue that discussion in the patch thread. Ronald _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
