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 lower extend 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().
---
libavcodec/get_bits.h | 13 +++++++------
1 files changed, 7 insertions(+), 6 deletions(-)
diff --git a/libavcodec/get_bits.h b/libavcodec/get_bits.h
index dd56308..e408e06 100644
--- a/libavcodec/get_bits.h
+++ b/libavcodec/get_bits.h
@@ -77,7 +77,7 @@ typedef struct GetBitContext {
uint32_t cache1;
int bit_count;
#endif
- int size_in_bits;
+ int size_in_bits, size_in_bits_plus1;
} GetBitContext;
#define VLC_TYPE int16_t
@@ -165,8 +165,8 @@ for examples see get_bits, show_bits, skip_bits, get_vlc
# define SKIP_COUNTER(name, gb, num) name##_index += (num)
#else
# define SKIP_COUNTER(name, gb, num) name##_index = \
- (gb)->size_in_bits - name##_index <=
(num) ? \
- (gb)->size_in_bits + 1 : name##_index +
(num)
+ (gb)->size_in_bits_plus1 - name##_index < (num) ? \
+ (gb)->size_in_bits_plus1 : name##_index + (num)
#endif
# define SKIP_BITS(name, gb, num) do { \
@@ -197,8 +197,8 @@ static inline void skip_bits_long(GetBitContext *s, int n){
#if UNCHECKED_BITSTREAM_READER
s->index += n;
#else
- s->index = s->size_in_bits - s->index <= n ?
- s->size_in_bits + 1 : s->index + n;
+ s->index = s->size_in_bits_plus1 - s->index < n ?
+ s->size_in_bits_plus1 : s->index + n;
#endif
}
@@ -346,7 +346,7 @@ static inline unsigned int get_bits1(GetBitContext *s){
result <<= index & 7;
result >>= 8 - 1;
#endif
- if (UNCHECKED_BITSTREAM_READER || s->index <= s->size_in_bits)
+ if (UNCHECKED_BITSTREAM_READER || s->index < s->size_in_bits_plus1)
index++;
s->index = index;
@@ -427,6 +427,7 @@ static inline void init_get_bits(GetBitContext *s,
s->buffer = buffer;
s->size_in_bits = bit_size;
+ s->size_in_bits_plus1 = bit_size + 1;
s->buffer_end = buffer + buffer_size;
#ifdef ALT_BITSTREAM_READER
s->index = 0;
--
1.7.6
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