path: root/tremor/framing.c

/********************************************************************
 *                                                                  *
 * THIS FILE IS PART OF THE OggVorbis SOFTWARE CODEC SOURCE CODE.   *
 * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS     *
 * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
 * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING.       *
 *                                                                  *
 * THE OggVorbis SOURCE CODE IS (C) COPYRIGHT 1994-2002             *
 * by the Xiph.Org Foundation http://www.xiph.org/                  *
 *                                                                  *
 ********************************************************************

 function: code raw [Vorbis] packets into framed OggSquish stream and
           decode Ogg streams back into raw packets
 last mod: $Id$

 note: The CRC code is directly derived from public domain code by
 Ross Williams (ross@guest.adelaide.edu.au).  See docs/framing.html
 for details.

 ********************************************************************/

#include <stdlib.h>
#include <string.h>
#include "ogg.h"

/* A complete description of Ogg framing exists in docs/framing.html */

int ogg_page_version(ogg_page *og){
  return((int)(og->header[4]));
}

int ogg_page_continued(ogg_page *og){
  return((int)(og->header[5]&0x01));
}

int ogg_page_bos(ogg_page *og){
  return((int)(og->header[5]&0x02));
}

int ogg_page_eos(ogg_page *og){
  return((int)(og->header[5]&0x04));
}

ogg_int64_t ogg_page_granulepos(ogg_page *og){
  unsigned char *page=og->header;
  ogg_int64_t granulepos=page[13]&(0xff);
  granulepos= (granulepos<<8)|(page[12]&0xff);
  granulepos= (granulepos<<8)|(page[11]&0xff);
  granulepos= (granulepos<<8)|(page[10]&0xff);
  granulepos= (granulepos<<8)|(page[9]&0xff);
  granulepos= (granulepos<<8)|(page[8]&0xff);
  granulepos= (granulepos<<8)|(page[7]&0xff);
  granulepos= (granulepos<<8)|(page[6]&0xff);
  return(granulepos);
}

int ogg_page_serialno(ogg_page *og){
  return(og->header[14] |
	 (og->header[15]<<8) |
	 (og->header[16]<<16) |
	 (og->header[17]<<24));
}
 
long ogg_page_pageno(ogg_page *og){
  return(og->header[18] |
	 (og->header[19]<<8) |
	 (og->header[20]<<16) |
	 (og->header[21]<<24));
}



/* returns the number of packets that are completed on this page (if
   the leading packet is begun on a previous page, but ends on this
   page, it's counted */

/* NOTE:
If a page consists of a packet begun on a previous page, and a new
packet begun (but not completed) on this page, the return will be:
  ogg_page_packets(page)   ==1, 
  ogg_page_continued(page) !=0

If a page happens to be a single packet that was begun on a
previous page, and spans to the next page (in the case of a three or
more page packet), the return will be: 
  ogg_page_packets(page)   ==0, 
  ogg_page_continued(page) !=0
*/

int ogg_page_packets(ogg_page *og){
  int i,n=og->header[26],count=0;
  for(i=0;i<n;i++)
    if(og->header[27+i]<255)count++;
  return(count);
}


#if 0
/* helper to initialize lookup for direct-table CRC (illustrative; we
   use the static init below) */

static ogg_uint32_t _ogg_crc_entry(unsigned long index){
  int           i;
  unsigned long r;

  r = index << 24;
  for (i=0; i<8; i++)
    if (r & 0x80000000UL)
      r = (r << 1) ^ 0x04c11db7; /* The same as the ethernet generator
				    polynomial, although we use an
				    unreflected alg and an init/final
				    of 0, not 0xffffffff */
    else
       r<<=1;
 return (r & 0xffffffffUL);
}
#endif

static const ogg_uint32_t crc_lookup[256]={
  0x00000000,0x04c11db7,0x09823b6e,0x0d4326d9,
  0x130476dc,0x17c56b6b,0x1a864db2,0x1e475005,
  0x2608edb8,0x22c9f00f,0x2f8ad6d6,0x2b4bcb61,
  0x350c9b64,0x31cd86d3,0x3c8ea00a,0x384fbdbd,
  0x4c11db70,0x48d0c6c7,0x4593e01e,0x4152fda9,
  0x5f15adac,0x5bd4b01b,0x569796c2,0x52568b75,
  0x6a1936c8,0x6ed82b7f,0x639b0da6,0x675a1011,
  0x791d4014,0x7ddc5da3,0x709f7b7a,0x745e66cd,
  0x9823b6e0,0x9ce2ab57,0x91a18d8e,0x95609039,
  0x8b27c03c,0x8fe6dd8b,0x82a5fb52,0x8664e6e5,
  0xbe2b5b58,0xbaea46ef,0xb7a96036,0xb3687d81,
  0xad2f2d84,0xa9ee3033,0xa4ad16ea,0xa06c0b5d,
  0xd4326d90,0xd0f37027,0xddb056fe,0xd9714b49,
  0xc7361b4c,0xc3f706fb,0xceb42022,0xca753d95,
  0xf23a8028,0xf6fb9d9f,0xfbb8bb46,0xff79a6f1,
  0xe13ef6f4,0xe5ffeb43,0xe8bccd9a,0xec7dd02d,
  0x34867077,0x30476dc0,0x3d044b19,0x39c556ae,
  0x278206ab,0x23431b1c,0x2e003dc5,0x2ac12072,
  0x128e9dcf,0x164f8078,0x1b0ca6a1,0x1fcdbb16,
  0x018aeb13,0x054bf6a4,0x0808d07d,0x0cc9cdca,
  0x7897ab07,0x7c56b6b0,0x71159069,0x75d48dde,
  0x6b93dddb,0x6f52c06c,0x6211e6b5,0x66d0fb02,
  0x5e9f46bf,0x5a5e5b08,0x571d7dd1,0x53dc6066,
  0x4d9b3063,0x495a2dd4,0x44190b0d,0x40d816ba,
  0xaca5c697,0xa864db20,0xa527fdf9,0xa1e6e04e,
  0xbfa1b04b,0xbb60adfc,0xb6238b25,0xb2e29692,
  0x8aad2b2f,0x8e6c3698,0x832f1041,0x87ee0df6,
  0x99a95df3,0x9d684044,0x902b669d,0x94ea7b2a,
  0xe0b41de7,0xe4750050,0xe9362689,0xedf73b3e,
  0xf3b06b3b,0xf771768c,0xfa325055,0xfef34de2,
  0xc6bcf05f,0xc27dede8,0xcf3ecb31,0xcbffd686,
  0xd5b88683,0xd1799b34,0xdc3abded,0xd8fba05a,
  0x690ce0ee,0x6dcdfd59,0x608edb80,0x644fc637,
  0x7a089632,0x7ec98b85,0x738aad5c,0x774bb0eb,
  0x4f040d56,0x4bc510e1,0x46863638,0x42472b8f,
  0x5c007b8a,0x58c1663d,0x558240e4,0x51435d53,
  0x251d3b9e,0x21dc2629,0x2c9f00f0,0x285e1d47,
  0x36194d42,0x32d850f5,0x3f9b762c,0x3b5a6b9b,
  0x0315d626,0x07d4cb91,0x0a97ed48,0x0e56f0ff,
  0x1011a0fa,0x14d0bd4d,0x19939b94,0x1d528623,
  0xf12f560e,0xf5ee4bb9,0xf8ad6d60,0xfc6c70d7,
  0xe22b20d2,0xe6ea3d65,0xeba91bbc,0xef68060b,
  0xd727bbb6,0xd3e6a601,0xdea580d8,0xda649d6f,
  0xc423cd6a,0xc0e2d0dd,0xcda1f604,0xc960ebb3,
  0xbd3e8d7e,0xb9ff90c9,0xb4bcb610,0xb07daba7,
  0xae3afba2,0xaafbe615,0xa7b8c0cc,0xa379dd7b,
  0x9b3660c6,0x9ff77d71,0x92b45ba8,0x9675461f,
  0x8832161a,0x8cf30bad,0x81b02d74,0x857130c3,
  0x5d8a9099,0x594b8d2e,0x5408abf7,0x50c9b640,
  0x4e8ee645,0x4a4ffbf2,0x470cdd2b,0x43cdc09c,
  0x7b827d21,0x7f436096,0x7200464f,0x76c15bf8,
  0x68860bfd,0x6c47164a,0x61043093,0x65c52d24,
  0x119b4be9,0x155a565e,0x18197087,0x1cd86d30,
  0x029f3d35,0x065e2082,0x0b1d065b,0x0fdc1bec,
  0x3793a651,0x3352bbe6,0x3e119d3f,0x3ad08088,
  0x2497d08d,0x2056cd3a,0x2d15ebe3,0x29d4f654,
  0xc5a92679,0xc1683bce,0xcc2b1d17,0xc8ea00a0,
  0xd6ad50a5,0xd26c4d12,0xdf2f6bcb,0xdbee767c,
  0xe3a1cbc1,0xe760d676,0xea23f0af,0xeee2ed18,
  0xf0a5bd1d,0xf464a0aa,0xf9278673,0xfde69bc4,
  0x89b8fd09,0x8d79e0be,0x803ac667,0x84fbdbd0,
  0x9abc8bd5,0x9e7d9662,0x933eb0bb,0x97ffad0c,
  0xafb010b1,0xab710d06,0xa6322bdf,0xa2f33668,
  0xbcb4666d,0xb8757bda,0xb5365d03,0xb1f740b4};

/* init the encode/decode logical stream state */

int ogg_stream_init(ogg_stream_state *os,int serialno){
  if(os){
    memset(os,0,sizeof(*os));
    os->body_storage=16*1024;
    os->body_data=_ogg_malloc(os->body_storage*sizeof(*os->body_data));

    os->lacing_storage=1024;
    os->lacing_vals=_ogg_malloc(os->lacing_storage*sizeof(*os->lacing_vals));
    os->granule_vals=_ogg_malloc(os->lacing_storage*sizeof(*os->granule_vals));

    os->serialno=serialno;

    return(0);
  }
  return(-1);
} 

/* _clear does not free os, only the non-flat storage within */
int ogg_stream_clear(ogg_stream_state *os){
  if(os){
    if(os->body_data)_ogg_free(os->body_data);
    if(os->lacing_vals)_ogg_free(os->lacing_vals);
    if(os->granule_vals)_ogg_free(os->granule_vals);

    memset(os,0,sizeof(*os));    
  }
  return(0);
} 

int ogg_stream_destroy(ogg_stream_state *os){
  if(os){
    ogg_stream_clear(os);
    _ogg_free(os);
  }
  return(0);
} 

/* Helpers for ogg_stream_encode; this keeps the structure and
   what's happening fairly clear */

static void _os_body_expand(ogg_stream_state *os,int needed){
  if(os->body_storage<=os->body_fill+needed){
    os->body_storage+=(needed+1024);
    os->body_data=_ogg_realloc(os->body_data,os->body_storage*sizeof(*os->body_data));
  }
}

static void _os_lacing_expand(ogg_stream_state *os,int needed){
  if(os->lacing_storage<=os->lacing_fill+needed){
    os->lacing_storage+=(needed+32);
    os->lacing_vals=_ogg_realloc(os->lacing_vals,os->lacing_storage*sizeof(*os->lacing_vals));
    os->granule_vals=_ogg_realloc(os->granule_vals,os->lacing_storage*sizeof(*os->granule_vals));
  }
}

/* checksum the page */
/* Direct table CRC; note that this will be faster in the future if we
   perform the checksum silmultaneously with other copies */

void ogg_page_checksum_set(ogg_page *og){
  if(og){
    ogg_uint32_t crc_reg=0;
    int i;

    /* safety; needed for API behavior, but not framing code */
    og->header[22]=0;
    og->header[23]=0;
    og->header[24]=0;
    og->header[25]=0;
    
    for(i=0;i<og->header_len;i++)
      crc_reg=(crc_reg<<8)^crc_lookup[((crc_reg >> 24)&0xff)^og->header[i]];
    for(i=0;i<og->body_len;i++)
      crc_reg=(crc_reg<<8)^crc_lookup[((crc_reg >> 24)&0xff)^og->body[i]];
    
    og->header[22]=(unsigned char)(crc_reg&0xff);
    og->header[23]=(unsigned char)((crc_reg>>8)&0xff);
    og->header[24]=(unsigned char)((crc_reg>>16)&0xff);
    og->header[25]=(unsigned char)((crc_reg>>24)&0xff);
  }
}

/* submit data to the internal buffer of the framing engine */
int ogg_stream_packetin(ogg_stream_state *os,ogg_packet *op){
  int lacing_vals=op->bytes/255+1,i;

  if(os->body_returned){
    /* advance packet data according to the body_returned pointer. We
       had to keep it around to return a pointer into the buffer last
       call */
    
    os->body_fill-=os->body_returned;
    if(os->body_fill)
      memmove(os->body_data,os->body_data+os->body_returned,
	      os->body_fill);
    os->body_returned=0;
  }
 
  /* make sure we have the buffer storage */
  _os_body_expand(os,op->bytes);
  _os_lacing_expand(os,lacing_vals);

  /* Copy in the submitted packet.  Yes, the copy is a waste; this is
     the liability of overly clean abstraction for the time being.  It
     will actually be fairly easy to eliminate the extra copy in the
     future */

  memcpy(os->body_data+os->body_fill,op->packet,op->bytes);
  os->body_fill+=op->bytes;

  /* Store lacing vals for this packet */
  for(i=0;i<lacing_vals-1;i++){
    os->lacing_vals[os->lacing_fill+i]=255;
    os->granule_vals[os->lacing_fill+i]=os->granulepos;
  }
  os->lacing_vals[os->lacing_fill+i]=(op->bytes)%255;
  os->granulepos=os->granule_vals[os->lacing_fill+i]=op->granulepos;

  /* flag the first segment as the beginning of the packet */
  os->lacing_vals[os->lacing_fill]|= 0x100;

  os->lacing_fill+=lacing_vals;

  /* for the sake of completeness */
  os->packetno++;

  if(op->e_o_s)os->e_o_s=1;

  return(0);
}

/* This will flush remaining packets into a page (returning nonzero),
   even if there is not enough data to trigger a flush normally
   (undersized page). If there are no packets or partial packets to
   flush, ogg_stream_flush returns 0.  Note that ogg_stream_flush will
   try to flush a normal sized page like ogg_stream_pageout; a call to
   ogg_stream_flush does not guarantee that all packets have flushed.
   Only a return value of 0 from ogg_stream_flush indicates all packet
   data is flushed into pages.

   since ogg_stream_flush will flush the last page in a stream even if
   it's undersized, you almost certainly want to use ogg_stream_pageout
   (and *not* ogg_stream_flush) unless you specifically need to flush 
   an page regardless of size in the middle of a stream. */

int ogg_stream_flush(ogg_stream_state *os,ogg_page *og){
  int i;
  int vals=0;
  int maxvals=(os->lacing_fill>255?255:os->lacing_fill);
  int bytes=0;
  long acc=0;
  ogg_int64_t granule_pos=os->granule_vals[0];

  if(maxvals==0)return(0);
  
  /* construct a page */
  /* decide how many segments to include */
  
  /* If this is the initial header case, the first page must only include
     the initial header packet */
  if(os->b_o_s==0){  /* 'initial header page' case */
    granule_pos=0;
    for(vals=0;vals<maxvals;vals++){
      if((os->lacing_vals[vals]&0x0ff)<255){
	vals++;
	break;
      }
    }
  }else{
    for(vals=0;vals<maxvals;vals++){
      if(acc>4096)break;
      acc+=os->lacing_vals[vals]&0x0ff;
      granule_pos=os->granule_vals[vals];
    }
  }
  
  /* construct the header in temp storage */
  memcpy(os->header,"OggS",4);
  
  /* stream structure version */
  os->header[4]=0x00;
  
  /* continued packet flag? */
  os->header[5]=0x00;
  if((os->lacing_vals[0]&0x100)==0)os->header[5]|=0x01;
  /* first page flag? */
  if(os->b_o_s==0)os->header[5]|=0x02;
  /* last page flag? */
  if(os->e_o_s && os->lacing_fill==vals)os->header[5]|=0x04;
  os->b_o_s=1;

  /* 64 bits of PCM position */
  for(i=6;i<14;i++){
    os->header[i]=(unsigned char)(granule_pos&0xff);
    granule_pos>>=8;
  }

  /* 32 bits of stream serial number */
  {
    long serialno=os->serialno;
    for(i=14;i<18;i++){
      os->header[i]=(unsigned char)(serialno&0xff);
      serialno>>=8;
    }
  }

  /* 32 bits of page counter (we have both counter and page header
     because this val can roll over) */
  if(os->pageno==-1)os->pageno=0; /* because someone called
				     stream_reset; this would be a
				     strange thing to do in an
				     encode stream, but it has
				     plausible uses */
  {
    long pageno=os->pageno++;
    for(i=18;i<22;i++){
      os->header[i]=(unsigned char)(pageno&0xff);
      pageno>>=8;
    }
  }
  
  /* zero for computation; filled in later */
  os->header[22]=0;
  os->header[23]=0;
  os->header[24]=0;
  os->header[25]=0;
  
  /* segment table */
  os->header[26]=(unsigned char)(vals&0xff);
  for(i=0;i<vals;i++)
    bytes+=os->header[i+27]=(unsigned char)(os->lacing_vals[i]&0xff);
  
  /* set pointers in the ogg_page struct */
  og->header=os->header;
  og->header_len=os->header_fill=vals+27;
  og->body=os->body_data+os->body_returned;
  og->body_len=bytes;
  
  /* advance the lacing data and set the body_returned pointer */
  
  os->lacing_fill-=vals;
  memmove(os->lacing_vals,os->lacing_vals+vals,os->lacing_fill*sizeof(*os->lacing_vals));
  memmove(os->granule_vals,os->granule_vals+vals,os->lacing_fill*sizeof(*os->granule_vals));
  os->body_returned+=bytes;
  
  /* calculate the checksum */
  
  ogg_page_checksum_set(og);

  /* done */
  return(1);
}


/* This constructs pages from buffered packet segments.  The pointers
returned are to static buffers; do not free. The returned buffers are
good only until the next call (using the same ogg_stream_state) */

int ogg_stream_pageout(ogg_stream_state *os, ogg_page *og){

  if((os->e_o_s&&os->lacing_fill) ||          /* 'were done, now flush' case */
     os->body_fill-os->body_returned > 4096 ||/* 'page nominal size' case */
     os->lacing_fill>=255 ||                  /* 'segment table full' case */
     (os->lacing_fill&&!os->b_o_s)){          /* 'initial header page' case */
        
    return(ogg_stream_flush(os,og));
  }
  
  /* not enough data to construct a page and not end of stream */
  return(0);
}

int ogg_stream_eos(ogg_stream_state *os){
  return os->e_o_s;
}

/* DECODING PRIMITIVES: packet streaming layer **********************/

/* This has two layers to place more of the multi-serialno and paging
   control in the application's hands.  First, we expose a data buffer
   using ogg_sync_buffer().  The app either copies into the
   buffer, or passes it directly to read(), etc.  We then call
   ogg_sync_wrote() to tell how many bytes we just added.

   Pages are returned (pointers into the buffer in ogg_sync_state)
   by ogg_sync_pageout().  The page is then submitted to
   ogg_stream_pagein() along with the appropriate
   ogg_stream_state* (ie, matching serialno).  We then get raw
   packets out calling ogg_stream_packetout() with a
   ogg_stream_state.  See the 'frame-prog.txt' docs for details and
   example code. */

/* initialize the struct to a known state */
int ogg_sync_init(ogg_sync_state *oy){
  if(oy){
    memset(oy,0,sizeof(*oy));
  }
  return(0);
}

/* clear non-flat storage within */
int ogg_sync_clear(ogg_sync_state *oy){
  if(oy){
    if(oy->data)_ogg_free(oy->data);
    ogg_sync_init(oy);
  }
  return(0);
}

int ogg_sync_destroy(ogg_sync_state *oy){
  if(oy){
    ogg_sync_clear(oy);
    _ogg_free(oy);
  }
  return(0);
}

char *ogg_sync_buffer(ogg_sync_state *oy, long size){

  /* first, clear out any space that has been previously returned */
  if(oy->returned){
    oy->fill-=oy->returned;
    if(oy->fill>0)
      memmove(oy->data,oy->data+oy->returned,oy->fill);
    oy->returned=0;
  }

  if(size>oy->storage-oy->fill){
    /* We need to extend the internal buffer */
    long newsize=size+oy->fill+4096; /* an extra page to be nice */

    if(oy->data)
      oy->data=_ogg_realloc(oy->data,newsize);
    else
      oy->data=_ogg_malloc(newsize);
    oy->storage=newsize;
  }

  /* expose a segment at least as large as requested at the fill mark */
  return((char *)oy->data+oy->fill);
}

int ogg_sync_wrote(ogg_sync_state *oy, long bytes){
  if(oy->fill+bytes>oy->storage)return(-1);
  oy->fill+=bytes;
  return(0);
}

/* sync the stream.  This is meant to be useful for finding page
   boundaries.

   return values for this:
  -n) skipped n bytes
   0) page not ready; more data (no bytes skipped)
   n) page synced at current location; page length n bytes
   
*/

long ogg_sync_pageseek(ogg_sync_state *oy,ogg_page *og){
  unsigned char *page=oy->data+oy->returned;
  unsigned char *next;
  long bytes=oy->fill-oy->returned;
  
  if(oy->headerbytes==0){
    int headerbytes,i;
    if(bytes<27)return(0); /* not enough for a header */
    
    /* verify capture pattern */
    if(memcmp(page,"OggS",4))goto sync_fail;
    
    headerbytes=page[26]+27;
    if(bytes<headerbytes)return(0); /* not enough for header + seg table */
    
    /* count up body length in the segment table */
    
    for(i=0;i<page[26];i++)
      oy->bodybytes+=page[27+i];
    oy->headerbytes=headerbytes;
  }
  
  if(oy->bodybytes+oy->headerbytes>bytes)return(0);
  
  /* The whole test page is buffered.  Verify the checksum */
  {
    /* Grab the checksum bytes, set the header field to zero */
    char chksum[4];
    ogg_page log;
    
    memcpy(chksum,page+22,4);
    memset(page+22,0,4);
    
    /* set up a temp page struct and recompute the checksum */
    log.header=page;
    log.header_len=oy->headerbytes;
    log.body=page+oy->headerbytes;
    log.body_len=oy->bodybytes;
    ogg_page_checksum_set(&log);
    
    /* Compare */
    if(memcmp(chksum,page+22,4)){
      /* D'oh.  Mismatch! Corrupt page (or miscapture and not a page
	 at all) */
      /* replace the computed checksum with the one actually read in */
      memcpy(page+22,chksum,4);
      
      /* Bad checksum. Lose sync */
      goto sync_fail;
    }
  }
  
  /* yes, have a whole page all ready to go */
  {
    unsigned char *page=oy->data+oy->returned;
    long bytes;

    if(og){
      og->header=page;
      og->header_len=oy->headerbytes;
      og->body=page+oy->headerbytes;
      og->body_len=oy->bodybytes;
    }

    oy->unsynced=0;
    oy->returned+=(bytes=oy->headerbytes+oy->bodybytes);
    oy->headerbytes=0;
    oy->bodybytes=0;
    return(bytes);
  }
  
 sync_fail:
  
  oy->headerbytes=0;
  oy->bodybytes=0;
  
  /* search for possible capture */
  next=memchr(page+1,'O',bytes-1);
  if(!next)
    next=oy->data+oy->fill;

  oy->returned=next-oy->data;
  return(-(next-page));
}

/* sync the stream and get a page.  Keep trying until we find a page.
   Suppress 'sync errors' after reporting the first.

   return values:
   -1) recapture (hole in data)
    0) need more data
    1) page returned

   Returns pointers into buffered data; invalidated by next call to
   _stream, _clear, _init, or _buffer */

int ogg_sync_pageout(ogg_sync_state *oy, ogg_page *og){

  /* all we need to do is verify a page at the head of the stream
     buffer.  If it doesn't verify, we look for the next potential
     frame */

  for(;;){
    long ret=ogg_sync_pageseek(oy,og);
    if(ret>0){
      /* have a page */
      return(1);
    }
    if(ret==0){
      /* need more data */
      return(0);
    }
    
    /* head did not start a synced page... skipped some bytes */
    if(!oy->unsynced){
      oy->unsynced=1;
      return(-1);
    }

    /* loop. keep looking */

  }
}

/* add the incoming page to the stream state; we decompose the page
   into packet segments here as well. */

int ogg_stream_pagein(ogg_stream_state *os, ogg_page *og){
  unsigned char *header=og->header;
  unsigned char *body=og->body;
  long           bodysize=og->body_len;
  int            segptr=0;

  int version=ogg_page_version(og);
  int continued=ogg_page_continued(og);
  int bos=ogg_page_bos(og);
  int eos=ogg_page_eos(og);
  ogg_int64_t granulepos=ogg_page_granulepos(og);
  int serialno=ogg_page_serialno(og);
  long pageno=ogg_page_pageno(og);
  int segments=header[26];
  
  /* clean up 'returned data' */
  {
    long lr=os->lacing_returned;
    long br=os->body_returned;

    /* body data */
    if(br){
      os->body_fill-=br;
      if(os->body_fill)
	memmove(os->body_data,os->body_data+br,os->body_fill);
      os->body_returned=0;
    }

    if(lr){
      /* segment table */
      if(os->lacing_fill-lr){
	memmove(os->lacing_vals,os->lacing_vals+lr,
		(os->lacing_fill-lr)*sizeof(*os->lacing_vals));
	memmove(os->granule_vals,os->granule_vals+lr,
		(os->lacing_fill-lr)*sizeof(*os->granule_vals));
      }
      os->lacing_fill-=lr;
      os->lacing_packet-=lr;
      os->lacing_returned=0;
    }
  }

  /* check the serial number */
  if(serialno!=os->serialno)return(-1);
  if(version>0)return(-1);

  _os_lacing_expand(os,segments+1);

  /* are we in sequence? */
  if(pageno!=os->pageno){
    int i;

    /* unroll previous partial packet (if any) */
    for(i=os->lacing_packet;i<os->lacing_fill;i++)
      os->body_fill-=os->lacing_vals[i]&0xff;
    os->lacing_fill=os->lacing_packet;

    /* make a note of dropped data in segment table */
    if(os->pageno!=-1){
      os->lacing_vals[os->lacing_fill++]=0x400;
      os->lacing_packet++;
    }
  }

  /* are we a 'continued packet' page?  If so, we may need to skip
     some segments */
  if(continued){
    if(os->lacing_fill<1 || 
       os->lacing_vals[os->lacing_fill-1]==0x400){
      bos=0;
      for(;segptr<segments;segptr++){
	int val=header[27+segptr];
	body+=val;
	bodysize-=val;
	if(val<255){
	  segptr++;
	  break;
	}
      }
    }
  }
  
  if(bodysize){
    _os_body_expand(os,bodysize);
    memcpy(os->body_data+os->body_fill,body,bodysize);
    os->body_fill+=bodysize;
  }

  {
    int saved=-1;
    while(segptr<segments){
      int val=header[27+segptr];
      os->lacing_vals[os->lacing_fill]=val;
      os->granule_vals[os->lacing_fill]=-1;
      
      if(bos){
	os->lacing_vals[os->lacing_fill]|=0x100;
	bos=0;
      }
      
      if(val<255)saved=os->lacing_fill;
      
      os->lacing_fill++;
      segptr++;
      
      if(val<255)os->lacing_packet=os->lacing_fill;
    }
  
    /* set the granulepos on the last granuleval of the last full packet */
    if(saved!=-1){
      os->granule_vals[saved]=granulepos;
    }

  }

  if(eos){
    os->e_o_s=1;
    if(os->lacing_fill>0)
      os->lacing_vals[os->lacing_fill-1]|=0x200;
  }

  os->pageno=pageno+1;

  return(0);
}

/* clear things to an initial state.  Good to call, eg, before seeking */
int ogg_sync_reset(ogg_sync_state *oy){
  oy->fill=0;
  oy->returned=0;
  oy->unsynced=0;
  oy->headerbytes=0;
  oy->bodybytes=0;
  return(0);
}

int ogg_stream_reset(ogg_stream_state *os){
  os->body_fill=0;
  os->body_returned=0;

  os->lacing_fill=0;
  os->lacing_packet=0;
  os->lacing_returned=0;

  os->header_fill=0;

  os->e_o_s=0;
  os->b_o_s=0;
  os->pageno=-1;
  os->packetno=0;
  os->granulepos=0;

  return(0);
}

int ogg_stream_reset_serialno(ogg_stream_state *os,int serialno){
  ogg_stream_reset(os);
  os->serialno=serialno;
  return(0);
}

static int _packetout(ogg_stream_state *os,ogg_packet *op,int adv){

  /* The last part of decode. We have the stream broken into packet
     segments.  Now we need to group them into packets (or return the
     out of sync markers) */

  int ptr=os->lacing_returned;

  if(os->lacing_packet<=ptr)return(0);

  if(os->lacing_vals[ptr]&0x400){
    /* we need to tell the codec there's a gap; it might need to
       handle previous packet dependencies. */
    os->lacing_returned++;
    os->packetno++;
    return(-1);
  }

  if(!op && !adv)return(1); /* just using peek as an inexpensive way
                               to ask if there's a whole packet
                               waiting */

  /* Gather the whole packet. We'll have no holes or a partial packet */
  {
    int size=os->lacing_vals[ptr]&0xff;
    int bytes=size;
    int eos=os->lacing_vals[ptr]&0x200; /* last packet of the stream? */
    int bos=os->lacing_vals[ptr]&0x100; /* first packet of the stream? */

    while(size==255){
      int val=os->lacing_vals[++ptr];
      size=val&0xff;
      if(val&0x200)eos=0x200;
      bytes+=size;
    }

    if(op){
      op->e_o_s=eos;
      op->b_o_s=bos;
      op->packet=os->body_data+os->body_returned;
      op->packetno=os->packetno;
      op->granulepos=os->granule_vals[ptr];
      op->bytes=bytes;
    }

    if(adv){
      os->body_returned+=bytes;
      os->lacing_returned=ptr+1;
      os->packetno++;
    }
  }
  return(1);
}

int ogg_stream_packetout(ogg_stream_state *os,ogg_packet *op){
  return _packetout(os,op,1);
}

int ogg_stream_packetpeek(ogg_stream_state *os,ogg_packet *op){
  return _packetout(os,op,0);
}

void ogg_packet_clear(ogg_packet *op) {
  _ogg_free(op->packet);
  memset(op, 0, sizeof(*op));
}