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first try of a handwritten get_cabac() for x86, this is 10-20% faster on P3 depening on if you try to subtract the START/STOP_TIMER overhead 

Originally committed as revision 6602 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer 2006-10-09 14:15:14 +00:00
parent 2a1a6b64a1
commit f7d0b68361
1 changed files with 85 additions and 0 deletions
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85
libavcodec/cabac.h
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@ -364,6 +364,90 @@ static inline void renorm_cabac_decoder_once(CABACContext *c){
static int get_cabac(CABACContext *c, uint8_t * const state){
//FIXME gcc generates duplicate load/stores for c->low and c->range
//START_TIMER
#ifdef ARCH_X86
int bit;
#define LOW "0"
#define RANGE "4"
#define LPS_RANGE "12"
#define LPS_STATE "12+2*66*4"
#define MPS_STATE "12+2*66*4+2*65"
#define BYTESTART "12+2*66*4+4*65"
#define BYTE "16+2*66*4+4*65"
#define BYTEEND "20+2*66*4+4*65"
asm volatile(
"movzbl (%1), %%eax \n\t"
"movl "RANGE "(%2), %%ebx \n\t"
"movl "RANGE "(%2), %%edx \n\t"
"shrl $23, %%ebx \n\t"
"leal "LPS_RANGE"(%2, %%eax, 4), %%esi \n\t"
"movzbl (%%ebx, %%esi), %%esi \n\t"
"shll $17, %%esi \n\t"
"movl "LOW "(%2), %%ebx \n\t"
//eax:state ebx:low, edx:range, esi:RangeLPS
"subl %%esi, %%edx \n\t"
"cmpl %%edx, %%ebx \n\t"
" ja 1f \n\t"
"cmp $0x2000000, %%edx \n\t" //FIXME avoidable
"setb %%cl \n\t"
"shl %%cl, %%edx \n\t"
"shl %%cl, %%ebx \n\t"
"movb "MPS_STATE"(%2, %%eax), %%cl \n\t"
"movb %%cl, (%1) \n\t"
//eax:state ebx:low, edx:range, esi:RangeLPS
"test %%bx, %%bx \n\t"
" jnz 2f \n\t"
"movl "BYTE "(%2), %%esi \n\t"
"subl $0xFFFF, %%ebx \n\t"
"movzwl (%%esi), %%ecx \n\t"
"bswap %%ecx \n\t"
"shrl $15, %%ecx \n\t"
"addl $2, %%esi \n\t"
"addl %%ecx, %%ebx \n\t"
"movl %%esi, "BYTE "(%2) \n\t"
"jmp 2f \n\t"
"1: \n\t"
//eax:state ebx:low, edx:range, esi:RangeLPS
"subl %%edx, %%ebx \n\t"
"movl %%esi, %%edx \n\t"
"shr $19, %%esi \n\t"
"movb " MANGLE(ff_h264_norm_shift) "(%%esi), %%cl \n\t"
"shll %%cl, %%ebx \n\t"
"shll %%cl, %%edx \n\t"
"movb "LPS_STATE"(%2, %%eax), %%cl \n\t"
"movb %%cl, (%1) \n\t"
"incl %%eax \n\t"
"test %%bx, %%bx \n\t"
" jnz 2f \n\t"
"movl "BYTE "(%2), %%ecx \n\t"
"movzwl (%%ecx), %%esi \n\t"
"bswap %%esi \n\t"
"shrl $15, %%esi \n\t"
"subl $0xFFFF, %%esi \n\t"
"addl $2, %%ecx \n\t"
"movl %%ecx, "BYTE "(%2) \n\t"
"leal -1(%%ebx), %%ecx \n\t"
"xorl %%ebx, %%ecx \n\t"
"shrl $17, %%ecx \n\t"
"movb " MANGLE(ff_h264_norm_shift) "(%%ecx), %%cl \n\t"
"neg %%cl \n\t"
"add $7, %%cl \n\t"
"shll %%cl , %%esi \n\t"
"addl %%esi, %%ebx \n\t"
"2: \n\t"
"movl %%edx, "RANGE "(%2) \n\t"
"movl %%ebx, "LOW "(%2) \n\t"
"andl $1, %%eax \n\t"
:"=&a"(bit) //FIXME this is fragile gcc either runs out of registers or misscompiles it (for example if "+a"(bit) or "+m"(*state) is used
:"r"(state), "r"(c)
: "%ecx", "%ebx", "%edx", "%esi"
);
#else
int s = *state;
int RangeLPS= c->lps_range[s][c->range>>(CABAC_BITS+7)]<<(CABAC_BITS+1);
int bit, lps_mask attribute_unused;
@ -417,6 +501,7 @@ asm(
if(!(c->low & CABAC_MASK))
refill2(c);
#endif
#endif
//STOP_TIMER("get_cabac")
return bit;
}