The main effect is actually code size reduction, due to the smaller
refill code (or difference in inlining decision), e.g. on Win32 of
{magicyuv,huffyuvdec,utvideodec}.o as follows:
19068/41460/16512 -> 18892/40760/16448
It should also be a small speedup (because it simplifies the address
computation), but no change was measured.
---
libavcodec/get_bits.h | 43 +++++++++++++++++++++++++------------------
1 file changed, 25 insertions(+), 18 deletions(-)
diff --git a/libavcodec/get_bits.h b/libavcodec/get_bits.h
index 59bfbdd88b..4f75f9dd84 100644
--- a/libavcodec/get_bits.h
+++ b/libavcodec/get_bits.h
@@ -91,10 +91,12 @@ typedef uint32_t cache_type;
typedef struct GetBitContext {
const uint8_t *buffer, *buffer_end;
#if CACHED_BITSTREAM_READER
+ const uint8_t *ptr;
cache_type cache;
unsigned bits_left;
+#else
+ int index; // Cached version advances ptr instead
#endif
- int index;
int size_in_bits;
int size_in_bits_plus8;
} GetBitContext;
@@ -253,7 +255,7 @@ static inline unsigned int show_bits(GetBitContext *s, int
n);
static inline int get_bits_count(const GetBitContext *s)
{
#if CACHED_BITSTREAM_READER
- return s->index - s->bits_left;
+ return 8*(s->ptr - s->buffer) - s->bits_left;
#else
return s->index;
#endif
@@ -263,42 +265,42 @@ static inline int get_bits_count(const GetBitContext *s)
static inline void refill_half(GetBitContext *s, int is_le)
{
#if !UNCHECKED_BITSTREAM_READER
- if (s->index >> 3 >= s->buffer_end - s->buffer)
+ if (s->ptr >= s->buffer_end)
return;
#endif
#if BITSTREAM_BITS == 32
if (s->bits_left > 16) {
if (is_le)
- s->cache |= (uint32_t)s->buffer[s->index >> 3] << s->bits_left;
+ s->cache |= (uint32_t)s->ptr[0] << s->bits_left;
else
- s->cache |= (uint32_t)s->buffer[s->index >> 3] << (32 - s->bits_left);
- s->index += 8;
+ s->cache |= (uint32_t)s->ptr[0] << (32 - s->bits_left);
+ s->ptr++;
s->bits_left += 8;
return;
}
#endif
if (is_le)
- s->cache |= (cache_type)AV_RL_HALF(s->buffer + (s->index >> 3)) <<
s->bits_left;
+ s->cache |= (cache_type)AV_RL_HALF(s->ptr) << s->bits_left;
else
- s->cache |= (cache_type)AV_RB_HALF(s->buffer + (s->index >> 3)) <<
(BITSTREAM_HBITS - s->bits_left);
- s->index += BITSTREAM_HBITS;
+ s->cache |= (cache_type)AV_RB_HALF(s->ptr) << (BITSTREAM_HBITS -
s->bits_left);
+ s->ptr += sizeof(s->cache)/2;
s->bits_left += BITSTREAM_HBITS;
}
static inline void refill_all(GetBitContext *s, int is_le)
{
#if !UNCHECKED_BITSTREAM_READER
- if (s->index >> 3 >= s->buffer_end - s->buffer)
+ if (s->ptr >= s->buffer_end)
return;
#endif
if (is_le)
- s->cache = AV_RL_ALL(s->buffer + (s->index >> 3));
+ s->cache = AV_RL_ALL(s->ptr);
else
- s->cache = AV_RB_ALL(s->buffer + (s->index >> 3));
- s->index += BITSTREAM_BITS;
+ s->cache = AV_RB_ALL(s->ptr);
+ s->ptr += sizeof(s->cache);
s->bits_left = BITSTREAM_BITS;
}
@@ -534,13 +536,12 @@ static inline void skip_bits(GetBitContext *s, int n)
else {
n -= s->bits_left;
s->cache = 0;
- s->bits_left = 0;
if (n >= BITSTREAM_BITS) {
- unsigned skip = (n / 8) * 8;
+ unsigned skip = n / 8;
- n -= skip;
- s->index += skip;
+ n -= 8*skip;
+ s->ptr += skip;
}
#ifdef BITSTREAM_READER_LE
refill_all(s, 1);
@@ -699,12 +700,14 @@ static inline int init_get_bits_xe(GetBitContext *s,
const uint8_t *buffer,
s->size_in_bits = bit_size;
s->size_in_bits_plus8 = bit_size + 8;
s->buffer_end = buffer + buffer_size;
- s->index = 0;
#if CACHED_BITSTREAM_READER
+ s->ptr = buffer;
s->cache = 0;
s->bits_left = 0;
refill_all(s, is_le);
+#else
+ s->index = 0;
#endif
return ret;
@@ -757,7 +760,11 @@ static inline const uint8_t *align_get_bits(GetBitContext
*s)
int n = -get_bits_count(s) & 7;
if (n)
skip_bits(s, n);
+#if CACHED_BITSTREAM_READER
+ return s->ptr;
+#else
return s->buffer + (s->index >> 3);
+#endif
}
/**
--
2.26.0
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