source: buchla-68k/orig/IOLIB/FTELL.C@ 6888aa2

/*
   =============================================================================
        ftell.c -- return current file position
        Version 7 -- 1987-10-28 -- D.N. Lynx Crowe
   =============================================================================
*/

#define DEBUGIT         0

#include "biosdefs.h"
#include "stdio.h"
#include "io.h"
#include "stddefs.h"

#if     DEBUGIT
extern  short   fsdebug;
#endif

extern  int     _filecl();

/*
   =============================================================================
        ftell(fp) -- return the current position of file 'fp'.
   =============================================================================
*/

long
ftell(fp)
register FILE *fp;
{
        register struct fcb *fcp;
        register struct channel *chp;
        register long dpos, pos, diff;

        if (fp EQ (FILE *)0L) {         /* see if we point at a FILE */

#if     DEBUGIT
        if (fsdebug)
                printf("ftell($%08.8lX):  ERROR - null FILE pointer\n", fp);
#endif

                return(0L);
        }

        if (!fp->_flags & _BUSY) {      /* see if it's open */

#if     DEBUGIT
        if (fsdebug)
                printf("ftell($%08.8lX):  ERROR - FILE not open\n", fp);
#endif

                return(0L);
        }

        chp = &chantab[fp->_unit];      /* point at the channel */

        if (chp->c_close NE _filecl) {  /* see if it's seekable */

#if     DEBUGIT
        if (fsdebug)
                printf("ftell($%08.8lX):  ERROR - FILE device not seekable\n",
                        fp);
#endif

                return(0L);
        }

        fcp = chp->c_arg;               /* point at the FCB */

        dpos = fcp->offset + (fcp->curlsn << FILESHFT);

        if (fp->_flags & _DIRTY)        /* adjust for the buffering */
                pos = dpos + (diff = ((long)fp->_bp - (long)fp->_buff));
        else if (fp->_bp)
                pos = dpos - (diff = ((long)fp->_bend - (long)fp->_bp));
        else
                pos = dpos;

#if     DEBUGIT
        if (fsdebug) {

                printf("ftell($%08.8lX):  flags=$%04.4X, buff=$%08.8lX, bp=$%08.8lX, bend=$%08.8lX\n",
                        fp, fp->_flags, fp->_buff, fp->_bp, fp->_bend);
        printf("ftell($%08.8lX):  fcp=$%08.8lX, pos=%ld, dpos=%ld, diff=%ld\n",
                        fp, fcp, pos, dpos, diff);
                printf("ftell($%08.8lX):  curlsn=%ld, offset=%u\n",
                        fp, fcp->curlsn, fcp->offset);

                if ((fp->_flags & _DIRTY) AND (fp->_bp EQ NULL))
                        printf("ftell($%08.8lX):  ERROR - file is DIRTY and bp is NULL\n",
                                fp);
        }
#endif

        return(pos);
}