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faster (and simpler) bitstream reader (in C) 

git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@3571 b3059339-0415-0410-9bf9-f77b7e298cf2
This commit is contained in:
michael 2001-12-17 21:53:49 +00:00
parent 61c3a3af34
commit 0b64a4a64a
2 changed files with 39 additions and 2 deletions
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8
liba52/bitstream.c
View File

@ -31,7 +31,12 @@
#define BUFFER_SIZE 4096
#ifdef ALT_BITSTREAM_READER
int indx=0;
uint32_t * buffer_start;
#else
static uint32_t * buffer_start;
#endif
uint32_t bits_left;
uint32_t current_word;
@ -43,6 +48,9 @@ void bitstream_set_ptr (uint8_t * buf)
align = (int)buf & 3;
buffer_start = (uint32_t *) (buf - align);
bits_left = 0;
#ifdef ALT_BITSTREAM_READER
indx=0;
#endif
bitstream_get (align * 8);
}

33
liba52/bitstream.h
View File

@ -21,6 +21,9 @@
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
// alternative (faster) bitstram reader (reades upto 3 bytes over the end of the input)
#define ALT_BITSTREAM_READER
/* (stolen from the kernel) */
#ifdef WORDS_BIGENDIAN
@ -46,18 +49,33 @@
# endif
#endif
#ifdef ALT_BITSTREAM_READER
extern uint32_t *buffer_start;
extern int indx;
#else
extern uint32_t bits_left;
extern uint32_t current_word;
#endif
void bitstream_set_ptr (uint8_t * buf);
uint32_t bitstream_get_bh(uint32_t num_bits);
int32_t bitstream_get_bh_2(uint32_t num_bits);
static inline uint32_t
bitstream_get(uint32_t num_bits)
bitstream_get(uint32_t num_bits) // note num_bits is practically a constant due to inlineing
{
#ifdef ALT_BITSTREAM_READER
uint32_t result= swab32( *(uint32_t *)(((uint8_t *)buffer_start)+(indx>>3)) );
result<<= (indx&0x07);
result>>= 32 - num_bits;
indx+= num_bits;
return result;
#else
uint32_t result;
if(num_bits < bits_left) {
result = (current_word << (32 - bits_left)) >> (32 - num_bits);
bits_left -= num_bits;
@ -65,11 +83,21 @@ bitstream_get(uint32_t num_bits)
}
return bitstream_get_bh(num_bits);
#endif
}
static inline int32_t
bitstream_get_2(uint32_t num_bits)
{
#ifdef ALT_BITSTREAM_READER
int32_t result= swab32( *(uint32_t *)(((uint8_t *)buffer_start)+(indx>>3)) );
result<<= (indx&0x07);
result>>= 32 - num_bits;
indx+= num_bits;
return result;
#else
int32_t result;
if(num_bits < bits_left) {
@ -79,4 +107,5 @@ bitstream_get_2(uint32_t num_bits)
}
return bitstream_get_bh_2(num_bits);
#endif
}