usr/src/libc/stdio/fseek.c

/*
 * Seek for standard library.  Coordinates with buffering.
 */

#include        <stdio.h>

long lseek();

fseek(iop, offset, ptrname)
        register FILE *iop;
        long offset;
{
        register int c;
        long p;

        iop->_flag &= ~_IOEOF;
        if (iop->_flag & _IOREAD) {
                if (ptrname < 2 && iop->_base && !(iop->_flag&_IONBF)) {
                        c = iop->_cnt;
                        p = offset;
                        if (ptrname == 0)
                                p += c - lseek(fileno(iop), 0L, 1);
                        else
                                offset -= c;
                        if (!(iop->_flag&_IORW) && c > 0 && p <= c
                            && p >= iop->_base - iop->_ptr){
                                iop->_ptr += (int) p;
                                iop->_cnt -= (int) p;
                                return(0);
                        }
                }
                if (iop->_flag & _IORW) {
                        iop->_ptr = iop->_base;
                        iop->_flag &= ~_IOREAD;
                }
                p = lseek(fileno(iop), offset, ptrname);
                iop->_cnt = 0;
        } else if(iop->_flag & (_IOWRT|_IORW)) {
                fflush(iop);
                if (iop->_flag & _IORW) {
                        iop->_cnt = 0;
                        iop->_flag &= ~_IOWRT;
                        iop->_ptr = iop->_base;
                }
                p = lseek(fileno(iop), offset, ptrname);
        }
        return(p==-1? -1: 0);
}