Single link files seeking fixes:

fix pcm exact seeking at very beginning (a rejected packet was being
interpreted as a negative pcm offset) and very end of files (short
final frames require processing from previous page's granulepos to get
length of final frame correct)

svn path=/trunk/vorbis/; revision=3115

1 files changed, 48 insertions, 1 deletions

diff --git a/lib/synthesis.c b/lib/synthesis.c
index 52cf51aa..6a032d32 100644
--- a/lib/synthesis.c
+++ b/lib/synthesis.c
@@ -11,7 +11,7 @@
  ********************************************************************
 
  function: single-block PCM synthesis
- last mod: $Id: synthesis.c,v 1.25 2001/12/20 01:00:30 segher Exp $
+ last mod: $Id: synthesis.c,v 1.26 2002/02/28 04:12:48 xiphmont Exp $
 
  ********************************************************************/
 
@@ -73,6 +73,53 @@ int vorbis_synthesis(vorbis_block *vb,ogg_packet *op){
   return(_mapping_P[type]->inverse(vb,b->mode[mode]));
 }
 
+/* used to track pcm position without actually performing decode.
+   Useful for sequential 'fast forward' */
+int vorbis_synthesis_trackonly(vorbis_block *vb,ogg_packet *op){
+  vorbis_dsp_state     *vd=vb->vd;
+  backend_lookup_state *b=vd->backend_state;
+  vorbis_info          *vi=vd->vi;
+  codec_setup_info     *ci=vi->codec_setup;
+  oggpack_buffer       *opb=&vb->opb;
+  int                   mode;
+ 
+  /* first things first.  Make sure decode is ready */
+  _vorbis_block_ripcord(vb);
+  oggpack_readinit(opb,op->packet,op->bytes);
+
+  /* Check the packet type */
+  if(oggpack_read(opb,1)!=0){
+    /* Oops.  This is not an audio data packet */
+    return(OV_ENOTAUDIO);
+  }
+
+  /* read our mode and pre/post windowsize */
+  mode=oggpack_read(opb,b->modebits);
+  if(mode==-1)return(OV_EBADPACKET);
+  
+  vb->mode=mode;
+  vb->W=ci->mode_param[mode]->blockflag;
+  if(vb->W){
+    vb->lW=oggpack_read(opb,1);
+    vb->nW=oggpack_read(opb,1);
+    if(vb->nW==-1)   return(OV_EBADPACKET);
+  }else{
+    vb->lW=0;
+    vb->nW=0;
+  }
+  
+  /* more setup */
+  vb->granulepos=op->granulepos;
+  vb->sequence=op->packetno-3; /* first block is third packet */
+  vb->eofflag=op->e_o_s;
+
+  /* no pcm */
+  vb->pcmend=0;
+  vb->pcm=NULL;
+
+  return(0);
+}
+
 long vorbis_packet_blocksize(vorbis_info *vi,ogg_packet *op){
   codec_setup_info     *ci=vi->codec_setup;
   oggpack_buffer       opb;