From:	Nate Eldredge <neldredge AT hmc DOT edu>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: help with a bit stream....
Date:	28 Mar 2000 16:07:13 -0800
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I suspect what you'd do is to have a buffer of at least one byte, then
return bits from this buffer, and refill it when empty.  Something
like:

int buf; /* we really only use one byte of it */
int bits_left = 0;

/* Note this reads the least significant bit first... it could be
   changed. */
int get_bit() {
        int bit;
        if (bits_left == 0) {
                buf = getc(input); /* read one byte */
                /* handle error or EOF case */
        }
        bit = buf & 1; /* get least significant bit */
        buf >>= 1;     /* shift for the next time */
        bits_left--;   /* and note that we've used one bit */
        return bit;
}

Presumably the code you have does the same thing, but associates a
buffer with each file (which is why there are the funny structs).
This allows you to get bits from multiple files at once.

Krogg <krogg DOT no DOT to DOT spam AT gtcom DOT net> writes:

> Jonathan Meunier wrote:
> > 
> > err, the read_bit() function should return:
> > return (( byte_to_process >> which_bit ) & 1 );
> > 
> > And which_bit should be between 0 and 7..
> > 
> >         .(Trancelucid).
> >           .  Jaune  .
> > 
> > Jonathan Meunier wrote:
> > >
> > > BYTE read_bit( BYTE byte_to_process, BYTE which_bit )
> > > {
> > >   return ( byte_to_process & ( 1 << which_bit );
> > > }
> 
> This method isnt what i am looking for....I know how
> to see the individual bits in a byte but i want to be
> able to say read the next n bits and see if they are 
> on or off....maybe i want the next 7 or the next 22
> bits....I found some code in the snippits archive
> that seems promising for this purpose but i am still
> trying to figure out how to implement it....
> 
> Its got functions like these: 
> 
> bfile * bfopen(char *name, char *mode);
> int     bfread(bfile *bf);
> void    bfwrite(int bit, bfile *bf);
> void    bfclose(bfile *bf);
> 
> and a struct like this:
> 
> typedef struct  {
>       FILE *  file;       /* for stream I/O   */
>       char    rbuf;       /* read bit buffer  */
>       char    rcnt;       /* read bit count   */
>       char    wbuf;       /* write bit buffer */
>       char    wcnt;       /* write bit count  */
> } bfile;
> 
> I am trying to figure out how to chop out the junk
> and use this,but if some one esle had some thing better
> i would welcome the help.
> 
> Thnaks.
>  
> 
> 
> 
> -- 
> 
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-- 

Nate Eldredge
neldredge AT hmc DOT edu

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