Described as variant 4 in the linked article. Results in faster and smaller code. Also, cases for the "refill_all" cases (usually when we want to empty/fill it) have been inlined. --- libavcodec/get_bits.h | 103 +++++++++++++++++------------------------- 1 file changed, 41 insertions(+), 62 deletions(-)
diff --git a/libavcodec/get_bits.h b/libavcodec/get_bits.h index da054ebfcb..baff86ecf6 100644 --- a/libavcodec/get_bits.h +++ b/libavcodec/get_bits.h @@ -153,11 +153,7 @@ static inline unsigned int show_bits(GetBitContext *s, int n); */ #if CACHED_BITSTREAM_READER -# if BITSTREAM_BITS == 32 -# define MIN_CACHE_BITS (32-7) -# else -# define MIN_CACHE_BITS 32 -# endif +# define MIN_CACHE_BITS (BITSTREAM_BITS-7) #elif defined LONG_BITSTREAM_READER # define MIN_CACHE_BITS 32 #else @@ -262,46 +258,21 @@ static inline int get_bits_count(const GetBitContext *s) } #if CACHED_BITSTREAM_READER -static inline void refill_half(GetBitContext *s, int is_le) +// See variant 4 in the following article: +// https://fgiesen.wordpress.com/2018/02/20/reading-bits-in-far-too-many-ways-part-2/ +static inline void refill_gb(GetBitContext *s, int is_le) { #if !UNCHECKED_BITSTREAM_READER 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->ptr[0] << s->bits_left; - else - 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->ptr) << s->bits_left; + s->cache |= (cache_type)AV_RL_ALL(s->ptr) << s->bits_left; else - 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->ptr >= s->buffer_end) - return; -#endif - - if (is_le) - s->cache = AV_RL_ALL(s->ptr); - else - s->cache = AV_RB_ALL(s->ptr); - s->ptr += sizeof(s->cache); - s->bits_left = BITSTREAM_BITS; + s->cache |= (cache_type)AV_RB_ALL(s->ptr) >> s->bits_left; + s->ptr += (BITSTREAM_BITS-1 - s->bits_left) >> 3; + s->bits_left |= BITSTREAM_BITS-8; } static inline cache_type get_val(GetBitContext *s, unsigned n, int is_le) @@ -374,9 +345,9 @@ static inline int get_xbits(GetBitContext *s, int n) if (n > s->bits_left) #ifdef BITSTREAM_READER_LE - refill_half(s, 1); + refill_gb(s, 1); #else - refill_half(s, 0); + refill_gb(s, 0); #endif #if BITSTREAM_BITS == 32 @@ -448,9 +419,9 @@ static inline unsigned int get_bits(GetBitContext *s, int n) av_assert2(n>0 && n<=32); if (n > s->bits_left) { #ifdef BITSTREAM_READER_LE - refill_half(s, 1); + refill_gb(s, 1); #else - refill_half(s, 0); + refill_gb(s, 0); #endif if (s->bits_left < BITSTREAM_HBITS) s->bits_left = n; @@ -486,7 +457,7 @@ static inline unsigned int get_bits_le(GetBitContext *s, int n) #if CACHED_BITSTREAM_READER av_assert2(n>0 && n<=32); if (n > s->bits_left) { - refill_half(s, 1); + refill_gb(s, 1); if (s->bits_left < BITSTREAM_HBITS) s->bits_left = n; } @@ -513,9 +484,9 @@ static inline unsigned int show_bits(GetBitContext *s, int n) #if CACHED_BITSTREAM_READER if (n > s->bits_left) #ifdef BITSTREAM_READER_LE - refill_half(s, 1); + refill_gb(s, 1); #else - refill_half(s, 0); + refill_gb(s, 0); #endif tmp = show_val(s, n); @@ -535,7 +506,6 @@ static inline void skip_bits(GetBitContext *s, int n) skip_remaining(s, n); else { n -= s->bits_left; - s->cache = 0; if (n >= BITSTREAM_BITS) { unsigned skip = n / 8; @@ -543,11 +513,14 @@ static inline void skip_bits(GetBitContext *s, int n) n -= 8*skip; s->ptr += skip; } + #ifdef BITSTREAM_READER_LE - refill_all(s, 1); + s->cache = AV_RL_ALL(s->ptr); #else - refill_all(s, 0); + s->cache = AV_RB_ALL(s->ptr); #endif + s->ptr += sizeof(cache_type); + s->bits_left = BITSTREAM_BITS; if (n) skip_remaining(s, n); } @@ -561,12 +534,15 @@ static inline void skip_bits(GetBitContext *s, int n) static inline unsigned int get_bits1(GetBitContext *s) { #if CACHED_BITSTREAM_READER - if (!s->bits_left) + if (!s->bits_left) { #ifdef BITSTREAM_READER_LE - refill_all(s, 1); + s->cache = AV_RL_ALL(s->ptr); #else - refill_all(s, 0); + s->cache = AV_RB_ALL(s->ptr); #endif + s->ptr += sizeof(cache_type); + s->bits_left = BITSTREAM_BITS; + } #ifdef BITSTREAM_READER_LE return get_val(s, 1, 1); @@ -621,20 +597,21 @@ static inline unsigned int get_bits_long(GetBitContext *s, int n) if (n > s->bits_left) { n -= s->bits_left; # ifdef BITSTREAM_READER_LE - left = s->bits_left; - ret = get_val(s, s->bits_left, 1); - refill_all(s, 1); + ret = s->cache & ((CACHE_TYPE(1) << s->bits_left) - 1); + s->cache = AV_RL_ALL(s->ptr); # else - ret = get_val(s, s->bits_left, 0); - refill_all(s, 0); + ret = s->cache >> (BITSTREAM_BITS - s->bits_left); + s->cache = AV_RB_ALL(s->ptr); # endif + s->ptr += sizeof(cache_type); + s->bits_left = BITSTREAM_BITS; // OK because consumed right after } -#ifdef BITSTREAM_READER_LE +# ifdef BITSTREAM_READER_LE ret = get_val(s, n, 1) << left | ret; -#else +# else ret = get_val(s, n, 0) | ret << n; -#endif +# endif return ret; #else @@ -725,10 +702,12 @@ static inline int init_get_bits_xe(GetBitContext *s, const uint8_t *buffer, s->buffer_end = buffer + buffer_size; #if CACHED_BITSTREAM_READER - s->ptr = buffer; - s->cache = 0; - s->bits_left = 0; - refill_all(s, is_le); + if (is_le) + s->cache = AV_RL_ALL(buffer); + else + s->cache = AV_RB_ALL(buffer); + s->ptr = buffer+sizeof(cache_type); + s->bits_left = BITSTREAM_BITS; #else s->index = 0; #endif -- 2.26.0 _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
