"Ronald S. Bultje" <[email protected]> writes:
> From: "Ronald S. Bultje" <[email protected]>
>
> Based on work (for GCI) by Aneesh Dogra <[email protected]>, and
> inspired by patch in Chromium by Chris Evans <[email protected]>.
>
> When turned on, H264/CAVLC gets ~15% (CVPCMNL1_SVA_C.264) slower for
> ultra-high-bitrate files, or ~2.5% (CVFI1_SVA_C.264) for lower-bitrate
> files. Other codecs are affected to a lesser extent because they are
> less optimized; e.g., VC-1 slows down by less than 1% (all on x86).
> The patch generated 3 extra instructions (cmp, cmovae and mov) per
> call to get_bits().
> ---
> configure | 2 ++
> libavcodec/get_bits.h | 48 ++++++++++++++++++++++++++++++++++++++++++++++--
> libavcodec/wmavoice.c | 2 ++
> 3 files changed, 50 insertions(+), 2 deletions(-)
[...]
> // FIXME name?
> +#if UNCHECKED_BITSTREAM_READER
> # define SKIP_COUNTER(name, gb, num) name##_index += (num)
> +#else
> +# define SKIP_COUNTER(name, gb, num) name##_index = \
> + (gb)->size_in_bits_plus1 - name##_index < (num) ? \
> + (gb)->size_in_bits_plus1 : name##_index + (num)
> +#endif
Why +1? Is this for the hypothetical decoders that require overreading?
Which are those, and why don't we fix them?
> # define SKIP_BITS(name, gb, num) do { \
> SKIP_CACHE(name, gb, num); \
> @@ -171,7 +197,12 @@ static inline int get_bits_count(const GetBitContext *s){
> }
>
> static inline void skip_bits_long(GetBitContext *s, int n){
> +#if UNCHECKED_BITSTREAM_READER
> s->index += n;
> +#else
> + s->index = s->size_in_bits_plus1 - s->index < n ?
> + s->size_in_bits_plus1 : s->index + n;
> +#endif
> }
>
> #elif defined A32_BITSTREAM_READER
> @@ -196,7 +227,9 @@ static inline void skip_bits_long(GetBitContext *s, int
> n){
> const uint32_t next = av_be2ne32(*name##_buffer_ptr); \
> name##_cache0 |= NEG_USR32(next, name##_bit_count); \
> name##_cache1 |= next << name##_bit_count; \
> - name##_buffer_ptr++; \
> + if (UNCHECKED_BITSTREAM_READER || \
> + name##_buffer_ptr < (const uint32_t *)(gb)->buffer_end) \
> + name##_buffer_ptr++; \
> name##_bit_count -= 32; \
> } \
> } while (0)
> @@ -230,7 +263,12 @@ static inline int get_bits_count(const GetBitContext *s)
> {
> static inline void skip_bits_long(GetBitContext *s, int n){
> OPEN_READER(re, s);
> re_bit_count += n;
> +#if UNCHECKED_BITSTREAM_READER
> re_buffer_ptr += re_bit_count>>5;
> +#else
> + re_buffer_ptr = FFMIN(re_buffer_ptr + (re_bit_count >> 5),
> + (const uint32_t *) s->buffer_end);
> +#endif
This addition can overflow.
--
Måns Rullgård
[email protected]
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