ref: 498fc0bda980d56b4e08017853e103ce5ad8bf16
parent: 21f7285015b06a6e4b10fd5fd09696f34995a352
author: Timothy B. Terriberry <[email protected]>
date: Sun Oct 21 14:14:29 EDT 2012
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