shithub: opusfile

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Fix end_offset tracking bug from 007ec4e4.

end_offset should be the _start_ of the last Opus page in a link,
 to guarantee we seek before it to have enough information to do
 end-trimming.
After the changes in 007ec4e4, it would be set to the start of the
 next link if we cached the last page granule position.

Also add more comments.

--- a/src/opusfile.c

+++ b/src/opusfile.c

@@ -846,7 +846,7 @@

      cur_serialno,_serialnos,_nserialnos);

     if(OP_UNLIKELY(ret<0))return ret;

   }

-  /*This implementation requires that difference between the first and last

+  /*This implementation requires that the difference between the first and last

      granule positions in each link be representable in a signed, 64-bit

      number, and that each link also have at least as many samples as the

      pre-skip requires.*/

@@ -995,6 +995,7 @@

     opus_int64  bisect;

     opus_int64  next;

     opus_int64  last;

+    ogg_int64_t end_offset;

     ogg_int64_t end_gp;

     int         sri;

     serialnos=*_serialnos;

@@ -1025,7 +1026,10 @@

     end_gp=-1;

     if(sri<nsr){

       _searched=_sr[sri].offset+_sr[sri].size;

-      if(_sr[sri].serialno==links[nlinks-1].serialno)end_gp=_sr[sri].gp;

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

+        end_gp=_sr[sri].gp;

+        end_offset=_sr[sri].offset;

+      }

     }

     nsr=sri;

     bisect=-1;

@@ -1049,8 +1053,12 @@

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

        links below.*/

     while(_searched<end_searched){

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

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

-      if(OP_UNLIKELY(bisect-_searched<OP_CHUNK_SIZE))bisect=_searched;

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

+      if(bisect-_searched<OP_CHUNK_SIZE)bisect=_searched;

+      /*Otherwise we're skipping data.

+        Forget the end page, if we saw one, as we might miss a later one.*/

       else end_gp=-1;

       ret=op_seek_helper(_of,bisect);

       if(OP_UNLIKELY(ret<0))return ret;

@@ -1075,7 +1083,13 @@

       }

       else{

         _searched=_of->offset;

-        if(_sr[nsr].serialno==links[nlinks-1].serialno)end_gp=_sr[nsr].gp;

+        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

+             looking for it later.*/

+          end_gp=_sr[nsr].gp;

+          end_offset=last;

+        }

       }

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

     }

@@ -1084,16 +1098,25 @@

        op_find_initial_pcm_offset() didn't already determine the link was

        empty.*/

     if(OP_LIKELY(links[nlinks-1].pcm_end==-1)){

+      if(end_gp==-1){

+        /*If we don't know where the end page is, we'll have to seek back and

+           look for it, starting from the end of the link.*/

+        end_offset=next;

+        /*Also forget the last page we read.

+          It won't be available after the seek.*/

+        last=-1;

+      }

       ret=op_find_final_pcm_offset(_of,serialnos,nserialnos,

-       links+nlinks-1,next,links[nlinks-1].serialno,end_gp,&total_duration);

+       links+nlinks-1,end_offset,links[nlinks-1].serialno,end_gp,

+       &total_duration);

       if(OP_UNLIKELY(ret<0))return ret;

-      if(end_gp==-1)last=-1;

     }

-    /*Restore the cursor position after the seek.

-      This only performs an actual seek if the last page in the link did not

-       belong to our Opus stream.

-      TODO: Read forward instead, or let seek implementations do that?*/

     if(last!=next){

+      /*The last page we read was not the first page the next link.

+        Move the cursor position to the offset of that first page.

+        This only performs an actual seek if the first page of the next link

+         does not start at the end of the last page from the current Opus

+         stream with a valid granule position.*/

       ret=op_seek_helper(_of,next);

       if(OP_UNLIKELY(ret<0))return ret;

     }