shithub: opusfile

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Bias the offsets in op_predict_link_start().

We apply a positive bias when the previous bisection point was
 inside the current link, causing us to scan forward a bit instead
 of seeking to a new location.
This knocks up to 18% off the number of seeks required to open very
 large files with lots of links.

--- a/src/opusfile.c

+++ b/src/opusfile.c

@@ -918,7 +918,7 @@

    records, assuming the initial granule position of any streams we've found is

    0.*/

 static opus_int64 op_predict_link_start(const OpusSeekRecord *_sr,int _nsr,

- opus_int64 _searched,opus_int64 _end_searched){

+ opus_int64 _searched,opus_int64 _end_searched,opus_int32 _bias){

   opus_int64 bisect;

   int        sri;

   int        srj;

@@ -969,7 +969,7 @@

       if(ipart>0&&(offset2-_searched)/ipart<num)continue;

       offset2-=ipart*num;

       gp2-=ipart*den;

-      offset2-=op_rescale64(gp2,den,num);

+      offset2-=op_rescale64(gp2,den,num)-_bias;

       if(offset2<_searched)continue;

       bisect=OP_MIN(bisect,offset2);

       break;

@@ -1065,6 +1065,7 @@

     /*We guard against garbage separating the last and first pages of two

        links below.*/

     while(_searched<end_searched){

+      opus_int32 next_bias;

       /*If we don't have a better estimate, use simple bisection.*/

       if(bisect==-1)bisect=_searched+(end_searched-_searched>>1);

       /*If we're within OP_CHUNK_SIZE of the start, scan forward.*/

@@ -1083,6 +1084,7 @@

       if(!op_lookup_serialno(_sr[nsr].serialno,serialnos,nserialnos)){

         end_searched=bisect;

         next=last;

+        next_bias=0;

         /*In reality we should always have enough room, but be paranoid.*/

         if(OP_LIKELY(nsr+1<_csr)){

           _sr[nsr].search_start=bisect;

@@ -1095,6 +1097,7 @@

       }

       else{

         _searched=_of->offset;

+        next_bias=OP_CHUNK_SIZE;

         if(_sr[nsr].serialno==links[nlinks-1].serialno){

           /*This page was from the stream we want, remember it.

             If it's the last such page in the link, we won't have to go back

@@ -1103,7 +1106,7 @@

           end_offset=last;

         }

       }

-      bisect=op_predict_link_start(_sr,nsr,_searched,end_searched);

+      bisect=op_predict_link_start(_sr,nsr,_searched,end_searched,next_bias);

     }

     /*Bisection point found.

       Get the final granule position of the previous link, assuming