pnmbitio.cxx

/*
 * bitio.c - bitstream I/O
 *
 * Works for (sizeof(unsigned long)-1)*8 bits.
 *
 * Copyright (C) 1992 by David W. Sanderson.
 * 
 * Permission to use, copy, modify, and distribute this software and its
 * documentation for any purpose and without fee is hereby granted,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  This software is provided "as is"
 * without express or implied warranty.
 */

#include "pnmbitio.h"
#include <assert.h>

using std::istream;
using std::ostream;

struct bitstream
{
        istream *inf;
        ostream *outf;
        unsigned long
                bitbuf;         /* bit buffer */
        int
                nbitbuf;        /* number of bits in 'bitbuf' */
        char
                mode;
};

#define Mask(n)         ((1<<(n))-1)

#define BitPut(b,ul,n)  ((b)->bitbuf = (((b)->bitbuf<<(n))      \
                                        |((ul)&Mask(n))),       \
                        (b)->nbitbuf += (n))

#define BitGet(b,n)     (((b)->bitbuf>>((b)->nbitbuf-=(n))) & Mask(n))

/*
 * pm_bitinit() - allocate and return a struct bitstream * for the
 * given FILE*.
 *
 * mode must be one of "r" or "w", according to whether you will be
 * reading from or writing to the struct bitstream *.
 *
 * Returns 0 on error.
 */

EXPCL_PANDA_PNMIMAGE struct bitstream *
pm_bitinit(istream *f, const char *mode)
{
        struct bitstream *ans = nullptr;

        if(!f || !mode || !*mode)
                return ans;
        if(strcmp(mode, "r"))
                return ans;

        ans = (struct bitstream *)calloc(1, sizeof(struct bitstream));
        if(ans)
        {
                ans->inf = f;
                ans->mode = *mode;
        }

        return ans;
}

EXPCL_PANDA_PNMIMAGE struct bitstream *
pm_bitinit(ostream *f, const char *mode)
{
        struct bitstream *ans = nullptr;

        if(!f || !mode || !*mode)
                return ans;
        if(strcmp(mode, "w"))
                return ans;

        ans = (struct bitstream *)calloc(1, sizeof(struct bitstream));
        if(ans)
        {
                ans->outf = f;
                ans->mode = *mode;
        }

        return ans;
}

/*
 * pm_bitfini() - deallocate the given struct bitstream *.
 *
 * You must call this after you are done with the struct bitstream *.
 * 
 * It may flush some bits left in the buffer.
 *
 * Returns the number of bytes written, -1 on error.
 */

EXPCL_PANDA_PNMIMAGE int
pm_bitfini(struct bitstream *b)
{
        int             nbyte = 0;

        if(!b)
                return -1;

        /* flush the output */
        if(b->mode == 'w')
        {
                /* flush the bits */
                if (b->nbitbuf < 0 || b->nbitbuf >= 8)
                {
                        /* pm_bitwrite() didn't work */
                        return -1;
                }

                /*
                 * If we get to here, nbitbuf is 0..7
                 */
                if(b->nbitbuf)
                {
                        char    c;

                        BitPut(b, 0, (long)8-(b->nbitbuf));
                        c = (char) BitGet(b, (long)8);
                        if(!b->outf->put(c))
                        {
                                return -1;
                        }
                        nbyte++;
                }
        }

        free(b);
        return nbyte;
}

/*
 * pm_bitread() - read the next nbits into *val from the given file.
 * 
 * The last pm_bitread() must be followed by a call to pm_bitfini().
 * 
 * Returns the number of bytes read, -1 on error.
 */

EXPCL_PANDA_PNMIMAGE int
pm_bitread(struct bitstream *b, unsigned long nbits, unsigned long *val)
{
        int             nbyte = 0;
        int             c;

        if(!b)
                return -1;

        #ifdef _DEBUG
          assert(((signed long)nbits) > 0);
        #endif
        
        while (b->nbitbuf < (signed long)nbits)
        {
                if((c = b->inf->get()) == EOF)
                {
                        return -1;
                }
                nbyte++;

                BitPut(b, c, (long) 8);
        }

        *val = BitGet(b, nbits);
        return nbyte;
}

/*
 * pm_bitwrite() - write the low nbits of val to the given file.
 * 
 * The last pm_bitwrite() must be followed by a call to pm_bitfini().
 * 
 * Returns the number of bytes written, -1 on error.
 */

EXPCL_PANDA_PNMIMAGE int
pm_bitwrite(struct bitstream *b, unsigned long nbits, unsigned long val)
{
        int             nbyte = 0;
        char            c;

        if(!b)
                return -1;

        BitPut(b, val, nbits);

        while (b->nbitbuf >= 8)
        {
                c = (char) BitGet(b, (long)8);

                if(!b->outf->put(c))
                {
                        return -1;
                }
                nbyte++;
        }

        return nbyte;
}