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

 *                                                                  *

 * THIS FILE IS PART OF THE OggVorbis 'TREMOR' 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 'TREMOR' SOURCE CODE IS (C) COPYRIGHT 1994-2002    *

 * BY THE Xiph.Org FOUNDATION http://www.xiph.org/                  *

 *                                                                  *

 ********************************************************************

  function: packing variable sized words into an octet stream

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

/* We're 'LSb' endian; if we write a word but read individual bits,

   then we'll read the lsb first */

#include <string.h>

#include <stdlib.h>

#include "misc.h"

#include "ogg.h"

static unsigned long mask[]=

{0x00000000,0x00000001,0x00000003,0x00000007,0x0000000f,

 0x0000001f,0x0000003f,0x0000007f,0x000000ff,0x000001ff,

 0x000003ff,0x000007ff,0x00000fff,0x00001fff,0x00003fff,

 0x00007fff,0x0000ffff,0x0001ffff,0x0003ffff,0x0007ffff,

 0x000fffff,0x001fffff,0x003fffff,0x007fffff,0x00ffffff,

 0x01ffffff,0x03ffffff,0x07ffffff,0x0fffffff,0x1fffffff,

 0x3fffffff,0x7fffffff,0xffffffff };

/* mark read process as having run off the end */

static void _adv_halt(oggpack_buffer *b){

  b->headptr=b->head->buffer->data+b->head->begin+b->head->length;

  b->headend=-1;

  b->headbit=0;

}

/* spans forward, skipping as many bytes as headend is negative; if

   headend is zero, simply finds next byte.  If we're up to the end

   of the buffer, leaves headend at zero.  If we've read past the end,

   halt the decode process. */

static void _span(oggpack_buffer *b){

  while(b->headend<1){

    if(b->head->next){

      b->count+=b->head->length;

      b->head=b->head->next;

      b->headptr=b->head->buffer->data+b->head->begin-b->headend; 

      b->headend+=b->head->length;      

    }else{

      /* we've either met the end of decode, or gone past it. halt

         only if we're past */

      if(b->headend<0 || b->headbit)

        /* read has fallen off the end */

        _adv_halt(b);

      break;

    }

  }

}

void oggpack_readinit(oggpack_buffer *b,ogg_reference *r){

  memset(b,0,sizeof(*b));

  b->tail=b->head=r;

  b->count=0;

  b->headptr=b->head->buffer->data+b->head->begin;

  b->headend=b->head->length;

  _span(b);

}

#define _lookspan()   while(!end){\

                        head=head->next;\

                        if(!head) return -1;\

                        ptr=head->buffer->data + head->begin;\

                        end=head->length;\

                      }

/* Read in bits without advancing the bitptr; bits <= 32 */

long oggpack_look(oggpack_buffer *b,int bits){

  unsigned long m=mask[bits];

  unsigned long ret;

  bits+=b->headbit;

  if(bits >= b->headend<<3){

    int            end=b->headend;

    unsigned char *ptr=b->headptr;

    ogg_reference *head=b->head;

    if(end<0)return -1;

    if(bits){

      _lookspan();

      ret=*ptr++>>b->headbit;

      if(bits>8){

        --end;

        _lookspan();

        ret|=*ptr++<<(8-b->headbit);  

        if(bits>16){

          --end;

          _lookspan();

          ret|=*ptr++<<(16-b->headbit);  

          if(bits>24){

            --end;

            _lookspan();

            ret|=*ptr++<<(24-b->headbit);  

            if(bits>32 && b->headbit){

              --end;

              _lookspan();

              ret|=*ptr<<(32-b->headbit);

            }

          }

        }

      }

    }

  }else{

    /* make this a switch jump-table */

    ret=b->headptr[0]>>b->headbit;

    if(bits>8){

      ret|=b->headptr[1]<<(8-b->headbit);  

      if(bits>16){

        ret|=b->headptr[2]<<(16-b->headbit);  

        if(bits>24){

          ret|=b->headptr[3]<<(24-b->headbit);  

          if(bits>32 && b->headbit)

            ret|=b->headptr[4]<<(32-b->headbit);

        }

      }

    }

  }

  ret&=m;

  return ret;

}

/* limited to 32 at a time */

void oggpack_adv(oggpack_buffer *b,int bits){

  bits+=b->headbit;

  b->headbit=bits&7;

  b->headptr+=bits/8;

  if((b->headend-=bits/8)<1)_span(b);

}

int oggpack_eop(oggpack_buffer *b){

  if(b->headend<0)return -1;

  return 0;

}

/* bits <= 32 */

long oggpack_read(oggpack_buffer *b,int bits){

  long ret=oggpack_look(b,bits);

  oggpack_adv(b,bits);

  return(ret);

}

long oggpack_bytes(oggpack_buffer *b){

  return(b->count+b->headptr-b->head->buffer->data-b->head->begin+

         (b->headbit+7)/8);

}

long oggpack_bits(oggpack_buffer *b){

  return((b->count+b->headptr-b->head->buffer->data-b->head->begin)*8+

         b->headbit);

}