static int _open_seekable2(OggVorbis_File *vf){
long serialno=vf->current_serialno,end;
long dataoffset=vf->offset;
ogg_page og;
/* we're partially open and have a first link header state in
storage in vf */
/* we can seek, so set out learning all about this file */
(vf->callbacks.seek_func)(vf->datasource,0,SEEK_END);
vf->offset=vf->end=(vf->callbacks.tell_func)(vf->datasource);
/* We get the offset for the last page of the physical bitstream.
Most OggVorbis files will contain a single logical bitstream */
end=_get_prev_page(vf,&og);
if(end<0){
ov_clear(vf);
return(end);
}
/* more than one logical bitstream? */
if(ogg_page_serialno(&og)!=serialno){
/* Chained bitstream. Bisect-search each logical bitstream
section. Do so based on serial number only */
if(_bisect_forward_serialno(vf,0,0,end+1,serialno,0)<0){
ov_clear(vf);
return(OV_EREAD);
}
}else{
/* Only one logical bitstream */
if(_bisect_forward_serialno(vf,0,end,end+1,serialno,0)){
ov_clear(vf);
return(OV_EREAD);
}
}
/* the initial header memory is referenced by vf after; don't free it */
_prefetch_all_headers(vf,dataoffset);
return(ov_raw_seek(vf,0));
}
/* finds each bitstream link one at a time using a bisection search
(has to begin by knowing the offset of the lb's initial page).
Recurses for each link so it can alloc the link storage after
finding them all, then unroll and fill the cache at the same time */
static int _bisect_forward_serialno(OggVorbis_File *vf,
ogg_int64_t begin,
ogg_int64_t searched,
ogg_int64_t end,
ogg_uint32_t currentno,
long m){
ogg_int64_t endsearched=end;
ogg_int64_t next=end;
ogg_page og={0,0,0,0};
ogg_int64_t ret;
/* the below guards against garbage seperating the last and
first pages of two links. */
while(searched<endsearched){
ogg_int64_t bisect;
if(endsearched-searched<CHUNKSIZE){
bisect=searched;
}else{
bisect=(searched+endsearched)/2;
}
_seek_helper(vf,bisect);
ret=_get_next_page(vf,&og,-1);
if(ret==OV_EREAD)return(OV_EREAD);
if(ret<0 || ogg_page_serialno(&og)!=currentno){
endsearched=bisect;
if(ret>=0)next=ret;
}else{
searched=ret+og.header_len+og.body_len;
}
ogg_page_release(&og);
}
_seek_helper(vf,next);
ret=_get_next_page(vf,&og,-1);
if(ret==OV_EREAD)return(OV_EREAD);
if(searched>=end || ret<0){
ogg_page_release(&og);
vf->links=m+1;
vf->offsets=_ogg_malloc((vf->links+1)*sizeof(*vf->offsets));
vf->serialnos=_ogg_malloc(vf->links*sizeof(*vf->serialnos));
vf->offsets[m+1]=searched;
}else{
ret=_bisect_forward_serialno(vf,next,vf->offset,
end,ogg_page_serialno(&og),m+1);
ogg_page_release(&og);
if(ret==OV_EREAD)return(OV_EREAD);
}
vf->offsets[m]=begin;
vf->serialnos[m]=currentno;
return(0);
}
