/************************************************************************
 * Copyright (C) 2002-2009, Xiph.org Foundation
 * Copyright (C) 2010, Robin Watts for Pinknoise Productions Ltd
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the names of the Xiph.org Foundation nor Pinknoise
 * Productions Ltd nor the names of its contributors may be used to
 * endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 ************************************************************************

 function: decode Ogg streams back into raw packets

 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"
#include "misc.h"


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

/* basic, centralized Ogg memory management based on linked lists of
   references to refcounted memory buffers.  References and buffers
   are both recycled.  Buffers are passed around and consumed in
   reference form. */

static ogg_buffer_state *ogg_buffer_create(void){
  ogg_buffer_state *bs=_ogg_calloc(1,sizeof(*bs));
  return bs;
}

/* destruction is 'lazy'; there may be memory references outstanding,
   and yanking the buffer state out from underneath would be
   antisocial.  Dealloc what is currently unused and have
   _release_one watch for the stragglers to come in.  When they do,
   finish destruction. */

/* call the helper while holding lock */
static void _ogg_buffer_destroy(ogg_buffer_state *bs){
  ogg_buffer *bt;
  ogg_reference *rt;

  if(bs->shutdown){

    bt=bs->unused_buffers;
    rt=bs->unused_references;

    while(bt){
      ogg_buffer *b=bt;
      bt=b->ptr.next;
      if(b->data)_ogg_free(b->data);
      _ogg_free(b);
    }
    bs->unused_buffers=0;
    while(rt){
      ogg_reference *r=rt;
      rt=r->next;
      _ogg_free(r);
    }
    bs->unused_references=0;

    if(!bs->outstanding)
      _ogg_free(bs);

  }
}

static void ogg_buffer_destroy(ogg_buffer_state *bs){
  bs->shutdown=1;
  _ogg_buffer_destroy(bs);
}

static ogg_buffer *_fetch_buffer(ogg_buffer_state *bs,long bytes){
  ogg_buffer    *ob;
  bs->outstanding++;

  /* do we have an unused buffer sitting in the pool? */
  if(bs->unused_buffers){
    ob=bs->unused_buffers;
    bs->unused_buffers=ob->ptr.next;

    /* if the unused buffer is too small, grow it */
    if(ob->size<bytes){
      ob->data=_ogg_realloc(ob->data,bytes);
      ob->size=bytes;
    }
  }else{
    /* allocate a new buffer */
    ob=_ogg_malloc(sizeof(*ob));
    ob->data=_ogg_malloc(bytes<16?16:bytes);
    ob->size=bytes;
  }

  ob->refcount=1;
  ob->ptr.owner=bs;
  return ob;
}

static ogg_reference *_fetch_ref(ogg_buffer_state *bs){
  ogg_reference *or;
  bs->outstanding++;

  /* do we have an unused reference sitting in the pool? */
  if(bs->unused_references){
    or=bs->unused_references;
    bs->unused_references=or->next;
  }else{
    /* allocate a new reference */
    or=_ogg_malloc(sizeof(*or));
  }

  or->begin=0;
  or->length=0;
  or->next=0;
  return or;
}

/* fetch a reference pointing to a fresh, initially continguous buffer
   of at least [bytes] length */
static ogg_reference *ogg_buffer_alloc(ogg_buffer_state *bs,long bytes){
  ogg_buffer    *ob=_fetch_buffer(bs,bytes);
  ogg_reference *or=_fetch_ref(bs);
  or->buffer=ob;
  return or;
}

/* enlarge the data buffer in the current link */
static void ogg_buffer_realloc(ogg_reference *or,long bytes){
  ogg_buffer    *ob=or->buffer;

  /* if the unused buffer is too small, grow it */
  if(ob->size<bytes){
    ob->data=_ogg_realloc(ob->data,bytes);
    ob->size=bytes;
  }
}

static void _ogg_buffer_mark_one(ogg_reference *or){
  or->buffer->refcount++;
}

/* increase the refcount of the buffers to which the reference points */
static void ogg_buffer_mark(ogg_reference *or){
  while(or){
    _ogg_buffer_mark_one(or);
    or=or->next;
  }
}

/* duplicate a reference (pointing to the same actual buffer memory)
   and increment buffer refcount.  If the desired segment is zero
   length, a zero length ref is returned. */
static ogg_reference *ogg_buffer_sub(ogg_reference *or,long length){
  ogg_reference *ret=0,*head=0;

  /* duplicate the reference chain; increment refcounts */
  while(or && length){
    ogg_reference *temp=_fetch_ref(or->buffer->ptr.owner);
    if(head)
      head->next=temp;
    else
      ret=temp;
    head=temp;
    head->buffer=or->buffer;
    head->begin=or->begin;
    head->length=length;
    if(head->length>or->length)
      head->length=or->length;

    length-=head->length;
    or=or->next;
  }

  ogg_buffer_mark(ret);
  return ret;
}

ogg_reference *ogg_buffer_dup(ogg_reference *or){
  ogg_reference *ret=0,*head=0;
  /* duplicate the reference chain; increment refcounts */
  while(or){
    ogg_reference *temp=_fetch_ref(or->buffer->ptr.owner);
    if(head)
      head->next=temp;
    else
      ret=temp;
    head=temp;
    head->buffer=or->buffer;
    head->begin=or->begin;
    head->length=or->length;
    or=or->next;
  }

  ogg_buffer_mark(ret);
  return ret;
}

/* split a reference into two references; 'return' is a reference to
   the buffer preceeding pos and 'head'/'tail' are the buffer past the
   split.  If pos is at or past the end of the passed in segment,
   'head/tail' are NULL */
static ogg_reference *ogg_buffer_split(ogg_reference **tail,
                                ogg_reference **head,long pos){

  /* walk past any preceeding fragments to one of:
     a) the exact boundary that seps two fragments
     b) the fragment that needs split somewhere in the middle */
  ogg_reference *ret=*tail;
  ogg_reference *or=*tail;

  while(or && pos>or->length){
    pos-=or->length;
    or=or->next;
  }

  if(!or || pos==0){

    return 0;

  }else{

    if(pos>=or->length){
      /* exact split, or off the end? */
      if(or->next){

        /* a split */
        *tail=or->next;
        or->next=0;

      }else{

        /* off or at the end */
        *tail=*head=0;

      }
    }else{

      /* split within a fragment */
      long lengthA=pos;
      long beginB=or->begin+pos;
      long lengthB=or->length-pos;

      /* make a new reference to tail the second piece */
      *tail=_fetch_ref(or->buffer->ptr.owner);

      (*tail)->buffer=or->buffer;
      (*tail)->begin=beginB;
      (*tail)->length=lengthB;
      (*tail)->next=or->next;
      _ogg_buffer_mark_one(*tail);
      if(head && or==*head)*head=*tail;

      /* update the first piece */
      or->next=0;
      or->length=lengthA;

    }
  }
  return ret;
}

static void ogg_buffer_release_one(ogg_reference *or){
  ogg_buffer *ob=or->buffer;
  ogg_buffer_state *bs=ob->ptr.owner;

  ob->refcount--;
  if(ob->refcount==0){
    bs->outstanding--; /* for the returned buffer */
    ob->ptr.next=bs->unused_buffers;
    bs->unused_buffers=ob;
  }

  bs->outstanding--; /* for the returned reference */
  or->next=bs->unused_references;
  bs->unused_references=or;

  _ogg_buffer_destroy(bs); /* lazy cleanup (if needed) */

}

/* release the references, decrease the refcounts of buffers to which
   they point, release any buffers with a refcount that drops to zero */
static void ogg_buffer_release(ogg_reference *or){
  while(or){
    ogg_reference *next=or->next;
    ogg_buffer_release_one(or);
    or=next;
  }
}

static ogg_reference *ogg_buffer_pretruncate(ogg_reference *or,long pos){
  /* release preceeding fragments we don't want */
  while(or && pos>=or->length){
    ogg_reference *next=or->next;
    pos-=or->length;
    ogg_buffer_release_one(or);
    or=next;
  }
  if (or) {
    or->begin+=pos;
    or->length-=pos;
  }
  return or;
}

static ogg_reference *ogg_buffer_walk(ogg_reference *or){
  if(!or)return NULL;
  while(or->next){
    or=or->next;
  }
  return(or);
}

/* *head is appended to the front end (head) of *tail; both continue to
   be valid pointers, with *tail at the tail and *head at the head */
static ogg_reference *ogg_buffer_cat(ogg_reference *tail, ogg_reference *head){
  if(!tail)return head;

  while(tail->next){
    tail=tail->next;
  }
  tail->next=head;
  return ogg_buffer_walk(head);
}

static void _positionB(oggbyte_buffer *b,int pos){
  if(pos<b->pos){
    /* start at beginning, scan forward */
    b->ref=b->baseref;
    b->pos=0;
    b->end=b->pos+b->ref->length;
    b->ptr=b->ref->buffer->data+b->ref->begin;
  }
}

static void _positionF(oggbyte_buffer *b,int pos){
  /* scan forward for position */
  while(pos>=b->end){
    /* just seek forward */
    b->pos+=b->ref->length;
    b->ref=b->ref->next;
    b->end=b->ref->length+b->pos;
    b->ptr=b->ref->buffer->data+b->ref->begin;
  }
}

static int oggbyte_init(oggbyte_buffer *b,ogg_reference *or){
  memset(b,0,sizeof(*b));
  if(or){
    b->ref=b->baseref=or;
    b->pos=0;
    b->end=b->ref->length;
    b->ptr=b->ref->buffer->data+b->ref->begin;
    return 0;
  }else
    return -1;
}

static void oggbyte_set4(oggbyte_buffer *b,ogg_uint32_t val,int pos){
  int i;
  _positionB(b,pos);
  for(i=0;i<4;i++){
    _positionF(b,pos);
    b->ptr[pos-b->pos]=val;
    val>>=8;
    ++pos;
  }
}

static unsigned char oggbyte_read1(oggbyte_buffer *b,int pos){
  _positionB(b,pos);
  _positionF(b,pos);
  return b->ptr[pos-b->pos];
}

static ogg_uint32_t oggbyte_read4(oggbyte_buffer *b,int pos){
  ogg_uint32_t ret;
  _positionB(b,pos);
  _positionF(b,pos);
  ret=b->ptr[pos-b->pos];
  _positionF(b,++pos);
  ret|=b->ptr[pos-b->pos]<<8;
  _positionF(b,++pos);
  ret|=b->ptr[pos-b->pos]<<16;
  _positionF(b,++pos);
  ret|=b->ptr[pos-b->pos]<<24;
  return ret;
}

static ogg_int64_t oggbyte_read8(oggbyte_buffer *b,int pos){
  ogg_int64_t ret;
  unsigned char t[7];
  int i;
  _positionB(b,pos);
  for(i=0;i<7;i++){
    _positionF(b,pos);
    t[i]=b->ptr[pos++ -b->pos];
  }

  _positionF(b,pos);
  ret=b->ptr[pos-b->pos];

  for(i=6;i>=0;--i)
    ret= ret<<8 | t[i];

  return ret;
}

/* Now we get to the actual framing code */

int ogg_page_version(ogg_page *og){
  oggbyte_buffer ob;
  if(oggbyte_init(&ob,og->header))return -1;
  return oggbyte_read1(&ob,4);
}

int ogg_page_continued(ogg_page *og){
  oggbyte_buffer ob;
  if(oggbyte_init(&ob,og->header))return -1;
  return oggbyte_read1(&ob,5)&0x01;
}

int ogg_page_bos(ogg_page *og){
  oggbyte_buffer ob;
  if(oggbyte_init(&ob,og->header))return -1;
  return oggbyte_read1(&ob,5)&0x02;
}

int ogg_page_eos(ogg_page *og){
  oggbyte_buffer ob;
  if(oggbyte_init(&ob,og->header))return -1;
  return oggbyte_read1(&ob,5)&0x04;
}

ogg_int64_t ogg_page_granulepos(ogg_page *og){
  oggbyte_buffer ob;
  if(oggbyte_init(&ob,og->header))return -1;
  return oggbyte_read8(&ob,6);
}

ogg_uint32_t ogg_page_serialno(ogg_page *og){
  oggbyte_buffer ob;
  if(oggbyte_init(&ob,og->header)) return 0xffffffffUL;
  return oggbyte_read4(&ob,14);
}

ogg_uint32_t ogg_page_pageno(ogg_page *og){
  oggbyte_buffer ob;
  if(oggbyte_init(&ob,og->header))return 0xffffffffUL;
  return oggbyte_read4(&ob,18);
}

/* 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;
  int n;
  int count=0;
  oggbyte_buffer ob;
  oggbyte_init(&ob,og->header);

  n=oggbyte_read1(&ob,26);
  for(i=0;i<n;i++)
    if(oggbyte_read1(&ob,27+i)<255)count++;
  return(count);
}

/* Static CRC calculation table.  See older code in CVS for dead
   run-time initialization code. */

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};

void ogg_sync_init(ogg_sync_state *oy){
  memset(oy,0,sizeof(*oy));
  oy->bufferpool=ogg_buffer_create();
}

ogg_sync_state *ogg_sync_create(void){
  ogg_sync_state *oy=_ogg_calloc(1,sizeof(*oy));
  memset(oy,0,sizeof(*oy));
  oy->bufferpool=ogg_buffer_create();
  return oy;
}

int ogg_sync_clear(ogg_sync_state *oy){
  if(oy){
    ogg_sync_reset(oy);
    ogg_buffer_destroy(oy->bufferpool);
    memset(oy,0,sizeof(*oy));
  }
  return OGG_SUCCESS;
}

int ogg_sync_destroy(ogg_sync_state *oy){
  if(oy){
    ogg_sync_reset(oy);
    ogg_buffer_destroy(oy->bufferpool);
    memset(oy,0,sizeof(*oy));
    _ogg_free(oy);
  }
  return OGG_SUCCESS;
}

unsigned char *ogg_sync_bufferin(ogg_sync_state *oy, long bytes){

  /* [allocate and] expose a buffer for data submission.

     If there is no head fragment
       allocate one and expose it
     else
       if the current head fragment has sufficient unused space
         expose it
       else
         if the current head fragment is unused
           resize and expose it
         else
           allocate new fragment and expose it
  */

  /* base case; fifo uninitialized */
  if(!oy->fifo_head){
    oy->fifo_head=oy->fifo_tail=ogg_buffer_alloc(oy->bufferpool,bytes);
    return oy->fifo_head->buffer->data;
  }

  /* space left in current fragment case */
  if(oy->fifo_head->buffer->size-
     oy->fifo_head->length-
     oy->fifo_head->begin >= bytes)
    return oy->fifo_head->buffer->data+
      oy->fifo_head->length+oy->fifo_head->begin;

  /* current fragment is unused, but too small */
  if(!oy->fifo_head->length){
    ogg_buffer_realloc(oy->fifo_head,bytes);
    return oy->fifo_head->buffer->data+oy->fifo_head->begin;
  }

  /* current fragment used/full; get new fragment */
  {
    ogg_reference *new=ogg_buffer_alloc(oy->bufferpool,bytes);
    oy->fifo_head->next=new;
    oy->fifo_head=new;
  }
  return oy->fifo_head->buffer->data;
}

int ogg_sync_wrote(ogg_sync_state *oy, long bytes){
  if(!oy->fifo_head)return OGG_EINVAL;
  if(oy->fifo_head->buffer->size-oy->fifo_head->length-oy->fifo_head->begin <
     bytes)return OGG_EINVAL;
  oy->fifo_head->length+=bytes;
  oy->fifo_fill+=bytes;
  return OGG_SUCCESS;
}

#ifndef ONLY_C
ogg_uint32_t _checksum(ogg_reference *or, int bytes);
#else
static ogg_uint32_t _checksum(ogg_reference *or, int bytes){
  ogg_uint32_t crc_reg=0;
  int j,post;

  while(or){
    unsigned char *data=or->buffer->data+or->begin;
    post=(bytes<or->length?bytes:or->length);
    for(j=0;j<post;++j)
      crc_reg=(crc_reg<<8)^crc_lookup[((crc_reg >> 24)&0xff)^data[j]];
    bytes-=j;
    or=or->next;
  }

  return crc_reg;
}
#endif

/* 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){
  oggbyte_buffer page;
  long           bytes,ret=0;

  ogg_page_release(og);

  bytes=oy->fifo_fill;
  oggbyte_init(&page,oy->fifo_tail);

  if(oy->headerbytes==0){
    if(bytes<27)goto sync_out; /* not enough for even a minimal header */

    /* verify capture pattern */
    if(oggbyte_read1(&page,0)!=(int)'O' ||
       oggbyte_read1(&page,1)!=(int)'g' ||
       oggbyte_read1(&page,2)!=(int)'g' ||
       oggbyte_read1(&page,3)!=(int)'S'    ) goto sync_fail;

    oy->headerbytes=oggbyte_read1(&page,26)+27;
  }
  if(bytes<oy->headerbytes)goto sync_out; /* not enough for header +
                                             seg table */
  if(oy->bodybytes==0){
    int i;
    /* count up body length in the segment table */
    for(i=0;i<oy->headerbytes-27;i++)
      oy->bodybytes+=oggbyte_read1(&page,27+i);
  }

  if(oy->bodybytes+oy->headerbytes>bytes)goto sync_out;

  /* we have what appears to be a complete page; last test: verify
     checksum */
  {
    ogg_uint32_t chksum=oggbyte_read4(&page,22);
    oggbyte_set4(&page,0,22);

    /* Compare checksums; memory continues to be common access */
    if(chksum!=_checksum(oy->fifo_tail,oy->bodybytes+oy->headerbytes)){

      /* D'oh.  Mismatch! Corrupt page (or miscapture and not a page
         at all). replace the computed checksum with the one actually
         read in; remember all the memory is common access */

      oggbyte_set4(&page,chksum,22);
      goto sync_fail;
    }
    oggbyte_set4(&page,chksum,22);
  }

  /* We have a page.  Set up page return. */
  if(og){
    /* set up page output */
    og->header=ogg_buffer_split(&oy->fifo_tail,&oy->fifo_head,oy->headerbytes);
    og->header_len=oy->headerbytes;
    og->body=ogg_buffer_split(&oy->fifo_tail,&oy->fifo_head,oy->bodybytes);
    og->body_len=oy->bodybytes;
  }else{
    /* simply advance */
    oy->fifo_tail=
      ogg_buffer_pretruncate(oy->fifo_tail,oy->headerbytes+oy->bodybytes);
    if(!oy->fifo_tail)oy->fifo_head=0;
  }

  ret=oy->headerbytes+oy->bodybytes;
  oy->unsynced=0;
  oy->headerbytes=0;
  oy->bodybytes=0;
  oy->fifo_fill-=ret;

  return ret;

 sync_fail:

  oy->headerbytes=0;
  oy->bodybytes=0;
  oy->fifo_tail=ogg_buffer_pretruncate(oy->fifo_tail,1);
  ret--;

  /* search forward through fragments for possible capture */
  while(oy->fifo_tail){
    /* invariant: fifo_cursor points to a position in fifo_tail */
    unsigned char *now=oy->fifo_tail->buffer->data+oy->fifo_tail->begin;
    unsigned char *next=memchr(now, 'O', oy->fifo_tail->length);

    if(next){
      /* possible capture in this segment */
      long bytes=next-now;
      oy->fifo_tail=ogg_buffer_pretruncate(oy->fifo_tail,bytes);
      ret-=bytes;
      break;
    }else{
      /* no capture.  advance to next segment */
      long bytes=oy->fifo_tail->length;
      ret-=bytes;
      oy->fifo_tail=ogg_buffer_pretruncate(oy->fifo_tail,bytes);
    }
  }
  if(!oy->fifo_tail)oy->fifo_head=0;
  oy->fifo_fill+=ret;

 sync_out:
  return ret;
}

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

   return values:
   OGG_HOLE) 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 */

  while(1){
    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 OGG_HOLE;
    }

    /* loop. keep looking */

  }
}

/* clear things to an initial state.  Good to call, eg, before seeking */
int ogg_sync_reset(ogg_sync_state *oy){

  ogg_buffer_release(oy->fifo_tail);
  oy->fifo_tail=0;
  oy->fifo_head=0;
  oy->fifo_fill=0;

  oy->unsynced=0;
  oy->headerbytes=0;
  oy->bodybytes=0;
  return OGG_SUCCESS;
}

void ogg_stream_init(ogg_stream_state *os, int serialno){
  memset(os, 0, sizeof(*os));
  os->serialno=serialno;
  os->pageno=-1;
}

ogg_stream_state *ogg_stream_create(int serialno){
  ogg_stream_state *os=_ogg_calloc(1,sizeof(*os));
  os->serialno=serialno;
  os->pageno=-1;
  return os;
}

int ogg_stream_clear(ogg_stream_state *os){
  if(os){
    ogg_buffer_release(os->header_tail);
    ogg_buffer_release(os->body_tail);
    memset(os,0,sizeof(*os));
  }
  return OGG_SUCCESS;
}

int ogg_stream_destroy(ogg_stream_state *os){
  if(os){
    ogg_buffer_release(os->header_tail);
    ogg_buffer_release(os->body_tail);
    memset(os,0,sizeof(*os));
    _ogg_free(os);
  }
  return OGG_SUCCESS;
}


#define FINFLAG 0x80000000UL
#define FINMASK 0x7fffffffUL

static void _next_lace(oggbyte_buffer *ob,ogg_stream_state *os){
  /* search ahead one lace */
  os->body_fill_next=0;
  while(os->laceptr<os->lacing_fill){
    int val=oggbyte_read1(ob,27+os->laceptr++);
    os->body_fill_next+=val;
    if(val<255){
      os->body_fill_next|=FINFLAG;
      os->clearflag=1;
      break;
    }
  }
}

static void _span_queued_page(ogg_stream_state *os){
  while( !(os->body_fill&FINFLAG) ){

    if(!os->header_tail)break;

    /* first flush out preceeding page header (if any).  Body is
       flushed as it's consumed, so that's not done here. */

    if(os->lacing_fill>=0)
      os->header_tail=ogg_buffer_pretruncate(os->header_tail,
                                             os->lacing_fill+27);
    os->lacing_fill=0;
    os->laceptr=0;
    os->clearflag=0;

    if(!os->header_tail){
      os->header_head=0;
      break;
    }else{

      /* process/prepare next page, if any */

      long pageno;
      oggbyte_buffer ob;
      ogg_page og;               /* only for parsing header values */
      og.header=os->header_tail; /* only for parsing header values */
      pageno=ogg_page_pageno(&og);

      oggbyte_init(&ob,os->header_tail);
      os->lacing_fill=oggbyte_read1(&ob,26);

      /* are we in sequence? */
      if(pageno!=os->pageno){
        if(os->pageno==-1) /* indicates seek or reset */
          os->holeflag=1;  /* set for internal use */
        else
          os->holeflag=2;  /* set for external reporting */

        os->body_tail=ogg_buffer_pretruncate(os->body_tail,
                                             os->body_fill);
        if(os->body_tail==0)os->body_head=0;
        os->body_fill=0;

      }

      if(ogg_page_continued(&og)){
        if(os->body_fill==0){
          /* continued packet, but no preceeding data to continue */
          /* dump the first partial packet on the page */
          _next_lace(&ob,os);
          os->body_tail=
            ogg_buffer_pretruncate(os->body_tail,os->body_fill_next&FINMASK);
          if(os->body_tail==0)os->body_head=0;
          /* set span flag */
          if(!os->spanflag && !os->holeflag)os->spanflag=2;
        }
      }else{
        if(os->body_fill>0){
          /* preceeding data to continue, but not a continued page */
          /* dump body_fill */
          os->body_tail=ogg_buffer_pretruncate(os->body_tail,
                                               os->body_fill);
          if(os->body_tail==0)os->body_head=0;
          os->body_fill=0;

          /* set espan flag */
          if(!os->spanflag && !os->holeflag)os->spanflag=2;
        }
      }

      if(os->laceptr<os->lacing_fill){
        os->granulepos=ogg_page_granulepos(&og);

        /* get current packet size & flag */
        _next_lace(&ob,os);
        os->body_fill+=os->body_fill_next; /* addition handles the flag fine;
                                             unsigned on purpose */
        /* ...and next packet size & flag */
        _next_lace(&ob,os);

      }

      os->pageno=pageno+1;
      os->e_o_s=ogg_page_eos(&og);
      os->b_o_s=ogg_page_bos(&og);

    }
  }
}

/* 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){

  int serialno=ogg_page_serialno(og);
  int version=ogg_page_version(og);

  /* check the serial number */
  if(serialno!=os->serialno){
    //ogg_page_release(og);
    return OGG_ESERIAL;
  }
  if(version>0){
    //ogg_page_release(og);
    return OGG_EVERSION;
  }

  /* add to fifos */
  if(!os->body_tail){
    os->body_tail=og->body;
    os->body_head=ogg_buffer_walk(og->body);
  }else{
    os->body_head=ogg_buffer_cat(os->body_head,og->body);
  }
  if(!os->header_tail){
    os->header_tail=og->header;
    os->header_head=ogg_buffer_walk(og->header);
    os->lacing_fill=-27;
  }else{
    os->header_head=ogg_buffer_cat(os->header_head,og->header);
  }

  memset(og,0,sizeof(*og));
  return OGG_SUCCESS;
}

int ogg_stream_reset(ogg_stream_state *os){

  ogg_buffer_release(os->header_tail);
  ogg_buffer_release(os->body_tail);
  os->header_tail=os->header_head=0;
  os->body_tail=os->body_head=0;

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

  os->body_fill=0;
  os->lacing_fill=0;

  os->holeflag=0;
  os->spanflag=0;
  os->clearflag=0;
  os->laceptr=0;
  os->body_fill_next=0;

  return OGG_SUCCESS;
}

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

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

  ogg_packet_release(op);
  _span_queued_page(os);

  if(os->holeflag){
    int temp=os->holeflag;
    if(os->clearflag)
      os->holeflag=0;
    else
      os->holeflag=1;
    if(temp==2){
      os->packetno++;
      return OGG_HOLE;
    }
  }
  if(os->spanflag){
    int temp=os->spanflag;
    if(os->clearflag)
      os->spanflag=0;
    else
      os->spanflag=1;
    if(temp==2){
      os->packetno++;
      return OGG_SPAN;
    }
  }

  if(!(os->body_fill&FINFLAG)) return 0;
  if(!op && !adv)return 1; /* just using peek as an inexpensive way
                               to ask if there's a whole packet
                               waiting */
  if(op){
    op->b_o_s=os->b_o_s;
    if(os->e_o_s && os->body_fill_next==0)
      op->e_o_s=os->e_o_s;
    else
      op->e_o_s=0;
    if( (os->body_fill&FINFLAG) && !(os->body_fill_next&FINFLAG) )
      op->granulepos=os->granulepos;
    else
      op->granulepos=-1;
    op->packetno=os->packetno;
  }

  if(adv){
    oggbyte_buffer ob;
    oggbyte_init(&ob,os->header_tail);

    /* split the body contents off */
    if(op){
      op->packet=ogg_buffer_split(&os->body_tail,&os->body_head,
				  os->body_fill&FINMASK);
      op->bytes=os->body_fill&FINMASK;
    }else{
      os->body_tail=ogg_buffer_pretruncate(os->body_tail,
					   os->body_fill&FINMASK);
      if(os->body_tail==0)os->body_head=0;
    }

    /* update lacing pointers */
    os->body_fill=os->body_fill_next;
    _next_lace(&ob,os);
  }else{
    if(op){
      op->packet=ogg_buffer_sub(os->body_tail,os->body_fill&FINMASK);
      op->bytes=os->body_fill&FINMASK;
    }
  }

  if(adv){
    os->packetno++;
    os->b_o_s=0;
  }

  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);
}

int ogg_packet_release(ogg_packet *op) {
  if(op){
    ogg_buffer_release(op->packet);
    memset(op, 0, sizeof(*op));
  }
  return OGG_SUCCESS;
}

int ogg_page_release(ogg_page *og) {
  if(og){
    ogg_buffer_release(og->header);
    ogg_buffer_release(og->body);
    memset(og, 0, sizeof(*og));
  }
  return OGG_SUCCESS;
}

void ogg_page_dup(ogg_page *dup,ogg_page *orig){
  dup->header_len=orig->header_len;
  dup->body_len=orig->body_len;
  dup->header=ogg_buffer_dup(orig->header);
  dup->body=ogg_buffer_dup(orig->body);
}