/********************************************************************
 *                                                                  *
 * THIS FILE IS PART OF THE Ogg CONTAINER 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 1994-2010             *
 * by the Xiph.Org Foundation http://www.xiph.org/                  *
 *                                                                  *
 ********************************************************************

 function: code raw packets into framed OggSquish stream and
           decode Ogg streams back into raw packets
 last mod: $Id: framing.c 18052 2011-08-04 17:57:02Z giles $

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

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

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

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

int64_t ogg_page_granulepos(const ogg_page *og){
  unsigned char *page=og->header;
  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(const ogg_page *og){
  return(og->header[14] |
         (og->header[15]<<8) |
         (og->header[16]<<16) |
         (og->header[17]<<24));
}

long ogg_page_pageno(const 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(const 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);
}


static const 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->lacing_storage=1024;

    os->body_data=malloc(os->body_storage*sizeof(*os->body_data));
    os->lacing_vals=malloc(os->lacing_storage*sizeof(*os->lacing_vals));
    os->granule_vals=malloc(os->lacing_storage*sizeof(*os->granule_vals));

    if(!os->body_data || !os->lacing_vals || !os->granule_vals){
      ogg_stream_clear(os);
      return -1;
    }

    os->serialno=serialno;

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

/* async/delayed error detection for the ogg_stream_state */
int ogg_stream_check(ogg_stream_state *os){
  if(!os || !os->body_data) return -1;
  return 0;
}

/* _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)
       free(os->body_data);
    if(os->lacing_vals)
       free(os->lacing_vals);
    if(os->granule_vals)
       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);
    free(os);
  }
  return(0);
}

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

static int _os_body_expand(ogg_stream_state *os,int needed){
  if(os->body_storage<=os->body_fill+needed){
    void *ret=realloc(os->body_data,(os->body_storage+needed+1024)*
                     sizeof(*os->body_data));
    if(!ret){
      ogg_stream_clear(os);
      return -1;
    }
    os->body_storage+=(needed+1024);
    os->body_data=ret;
  }
  return 0;
}

static int _os_lacing_expand(ogg_stream_state *os,int needed){
  if(os->lacing_storage<=os->lacing_fill+needed){
    void *ret=realloc(os->lacing_vals,(os->lacing_storage+needed+32)*
                     sizeof(*os->lacing_vals));
    if(!ret){
      ogg_stream_clear(os);
      return -1;
    }
    os->lacing_vals=ret;
    ret=realloc(os->granule_vals,(os->lacing_storage+needed+32)*
                     sizeof(*os->granule_vals));
    if(!ret){
      ogg_stream_clear(os);
      return -1;
    }
    os->granule_vals=ret;
    os->lacing_storage+=(needed+32);
  }
  return 0;
}

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

void ogg_page_checksum_set(ogg_page *og){
  if(og){
    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_iovecin(ogg_stream_state *os, ogg_iovec_t *iov, int count,
                       long e_o_s, int64_t granulepos){

  int bytes = 0, lacing_vals, i;

  if(ogg_stream_check(os)) return -1;
  if(!iov) return 0;

  for (i = 0; i < count; ++i) bytes += (int)iov[i].iov_len;
  lacing_vals=bytes/255+1;

  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 */
  if(_os_body_expand(os,bytes) || _os_lacing_expand(os,lacing_vals))
    return -1;

  /* 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 */

  for (i = 0; i < count; ++i) {
    memcpy(os->body_data+os->body_fill, iov[i].iov_base, iov[i].iov_len);
    os->body_fill += (int)iov[i].iov_len;
  }

  /* 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]=bytes%255;
  os->granulepos=os->granule_vals[os->lacing_fill+i]=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(e_o_s)os->e_o_s=1;

  return(0);
}

int ogg_stream_packetin(ogg_stream_state *os,ogg_packet *op){
  ogg_iovec_t iov;
  iov.iov_base = op->packet;
  iov.iov_len = op->bytes;
  return ogg_stream_iovecin(os, &iov, 1, op->e_o_s, op->granulepos);
}

/* Conditionally flush a page; force==0 will only flush nominal-size
   pages, force==1 forces us to flush a page regardless of page size
   so long as there's any data available at all. */
static int ogg_stream_flush_i(ogg_stream_state *os,ogg_page *og, int force, int nfill){
  int i;
  int vals=0;
  int maxvals=(os->lacing_fill>255?255:os->lacing_fill);
  int bytes=0;
  long acc=0;
  int64_t granule_pos=-1;

  if(ogg_stream_check(os)) return(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{

    /* The extra packets_done, packet_just_done logic here attempts to do two things:
       1) Don't unneccessarily span pages.
       2) Unless necessary, don't flush pages if there are less than four packets on
          them; this expands page size to reduce unneccessary overhead if incoming packets
          are large.
       These are not necessary behaviors, just 'always better than naive flushing'
       without requiring an application to explicitly request a specific optimized
       behavior. We'll want an explicit behavior setup pathway eventually as well. */

    int packets_done=0;
    int packet_just_done=0;
    for(vals=0;vals<maxvals;vals++){
      if(acc>nfill && packet_just_done>=4){
        force=1;
        break;
      }
      acc+=os->lacing_vals[vals]&0x0ff;
      if((os->lacing_vals[vals]&0xff)<255){
        granule_pos=os->granule_vals[vals];
        packet_just_done=++packets_done;
      }else
        packet_just_done=0;
    }
    if(vals==255)force=1;
  }

  if(!force) return(0);

  /* 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 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
   a page regardless of size in the middle of a stream. */

int ogg_stream_flush(ogg_stream_state *os,ogg_page *og){
  return ogg_stream_flush_i(os,og,1,4096);
}

/* Like the above, but an argument is provided to adjust the nominal
   page size for applications which are smart enough to provide their
   own delay based flushing */

int ogg_stream_flush_fill(ogg_stream_state *os,ogg_page *og, int nfill){
  return ogg_stream_flush_i(os,og,1,nfill);
}

/* 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){
  int force=0;
  if(ogg_stream_check(os)) return 0;

  if((os->e_o_s&&os->lacing_fill) ||          /* 'were done, now flush' case */
     (os->lacing_fill&&!os->b_o_s))           /* 'initial header page' case */
    force=1;

  return(ogg_stream_flush_i(os,og,force,4096));
}

/* Like the above, but an argument is provided to adjust the nominal
page size for applications which are smart enough to provide their
own delay based flushing */

int ogg_stream_pageout_fill(ogg_stream_state *os, ogg_page *og, int nfill){
  int force=0;
  if(ogg_stream_check(os)) return 0;

  if((os->e_o_s&&os->lacing_fill) ||          /* 'were done, now flush' case */
     (os->lacing_fill&&!os->b_o_s))           /* 'initial header page' case */
    force=1;

  return(ogg_stream_flush_i(os,og,force,nfill));
}

int ogg_stream_eos(ogg_stream_state *os){
  if(ogg_stream_check(os)) return 1;
  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. */

/* initialize the struct to a known state */
int ogg_sync_init(ogg_sync_state *oy){
  if(oy){
    oy->storage = -1; /* used as a readiness flag */
    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)
       free(oy->data);
    memset(oy,0,sizeof(*oy));
  }
  return(0);
}

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

int ogg_sync_check(ogg_sync_state *oy){
  if(oy->storage<0) return -1;
  return 0;
}

char *ogg_sync_buffer(ogg_sync_state *oy, long size){
  if(ogg_sync_check(oy)) return NULL;

  /* 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 */
    void *ret;

    if(oy->data)
      ret=realloc(oy->data,newsize);
    else
      ret=malloc(newsize);
    if(!ret){
      ogg_sync_clear(oy);
      return NULL;
    }
    oy->data=ret;
    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(ogg_sync_check(oy))return -1;
  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(ogg_sync_check(oy))return 0;

  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=(int)(next-oy->data);
  return((long)-(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){

  if(ogg_sync_check(oy))return 0;

  /* 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);
  int64_t granulepos=ogg_page_granulepos(og);
  int serialno=ogg_page_serialno(og);
  long pageno=ogg_page_pageno(og);
  int segments=header[26];

  if(ogg_stream_check(os)) return -1;

  /* 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);

  if(_os_lacing_expand(os,segments+1)) return -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){
    if(_os_body_expand(os,bodysize)) return -1;
    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){
  if(ogg_sync_check(oy))return -1;

  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){
  if(ogg_stream_check(os)) return -1;

  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){
  if(ogg_stream_check(os)) return -1;
  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;
    long 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){
  if(ogg_stream_check(os)) return 0;
  return _packetout(os,op,1);
}

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

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