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/*-

 * Copyright (c) 1990, 1993

 *      The Regents of the University of California.  All rights reserved.

 *

 * This code is derived from software contributed to Berkeley by

 * Chris Torek.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 * 3. All advertising materials mentioning features or use of this software

 *    must display the following acknowledgement:

 *      This product includes software developed by the University of

 *      California, Berkeley and its contributors.

 * 4. Neither the name of the University nor the names of its contributors

 *    may be used to endorse or promote products derived from this software

 *    without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND

 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE

 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

 * SUCH DAMAGE.

 */

#if defined(LIBC_SCCS) && !defined(lint)

#if 0

static char sccsid[] = "@(#)fseek.c     8.3 (Berkeley) 1/2/94";

#endif

static const char rcsid[] =

                "$\Id: fseek.c,v 1.4 1996/06/22 10:33:22 jraynard Exp $";

#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <stdio.h>

#include <stdlib.h>

#include <errno.h>

#include "local.h"

#ifdef _THREAD_SAFE

#include <pthread.h>

#include "pthread_private.h"

#endif

#define POS_ERR (-(fpos_t)1)

/*

 * Seek the given file to the given offset.

 * `Whence' must be one of the three SEEK_* macros.

 */

int

fseek(fp, offset, whence)

        register FILE *fp;

        long offset;

        int whence;

{

        register fpos_t (*seekfn) __P((void *, fpos_t, int));

        fpos_t target, curoff;

        size_t n;

        struct stat st;

        int havepos;

        /* make sure stdio is set up */

        if (!__sdidinit)

                __sinit();

#ifdef _THREAD_SAFE

        _thread_flockfile(fp,__FILE__,__LINE__);

#endif

        /*

         * Have to be able to seek.

         */

        if ((seekfn = fp->_seek) == NULL) {

                errno = ESPIPE;                 /* historic practice */

                return (EOF);

        }

        /*

         * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.

         * After this, whence is either SEEK_SET or SEEK_END.

         */

        switch (whence) {

        case SEEK_CUR:

                /*

                 * In order to seek relative to the current stream offset,

                 * we have to first find the current stream offset a la

                 * ftell (see ftell for details).

                 */

                if (fp->_flags & __SOFF)

                        curoff = fp->_offset;

                else {

                        curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);

                        if (curoff == -1) {

#ifdef _THREAD_SAFE

                                _thread_funlockfile(fp);

#endif

                                return (EOF);

                        }

                }

                if (fp->_flags & __SRD) {

                        curoff -= fp->_r;

                        if (HASUB(fp))

                                curoff -= fp->_ur;

                } else if (fp->_flags & __SWR && fp->_p != NULL)

                        curoff += fp->_p - fp->_bf._base;

                offset += curoff;

                whence = SEEK_SET;

                havepos = 1;

                break;

        case SEEK_SET:

        case SEEK_END:

                curoff = 0;             /* XXX just to keep gcc quiet */

                havepos = 0;

                break;

        default:

                errno = EINVAL;

#ifdef _THREAD_SAFE

                _thread_funlockfile(fp);

#endif

                return (EOF);

        }

        /*

         * Can only optimise if:

         *      reading (and not reading-and-writing);

         *      not unbuffered; and

         *      this is a `regular' Unix file (and hence seekfn==__sseek).

         * We must check __NBF first, because it is possible to have __NBF

         * and __SOPT both set.

         */

        if (fp->_bf._base == NULL)

                __smakebuf(fp);

        if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))

                goto dumb;

        if ((fp->_flags & __SOPT) == 0) {

                if (seekfn != __sseek ||

                    fp->_file < 0 || fstat(fp->_file, &st) ||

                    (st.st_mode & S_IFMT) != S_IFREG) {

                        fp->_flags |= __SNPT;

                        goto dumb;

                }

                fp->_blksize = st.st_blksize;

                fp->_flags |= __SOPT;

        }

        /*

         * We are reading; we can try to optimise.

         * Figure out where we are going and where we are now.

         */

        if (whence == SEEK_SET)

                target = offset;

        else {

                if (fstat(fp->_file, &st))

                        goto dumb;

                target = st.st_size + offset;

        }

        if (!havepos) {

                if (fp->_flags & __SOFF)

                        curoff = fp->_offset;

                else {

                        curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);

                        if (curoff == POS_ERR)

                                goto dumb;

                }

                curoff -= fp->_r;

                if (HASUB(fp))

                        curoff -= fp->_ur;

        }

        /*

         * Compute the number of bytes in the input buffer (pretending

         * that any ungetc() input has been discarded).  Adjust current

         * offset backwards by this count so that it represents the

         * file offset for the first byte in the current input buffer.

         */

        if (HASUB(fp)) {

                curoff += fp->_r;       /* kill off ungetc */

                n = fp->_up - fp->_bf._base;

                curoff -= n;

                n += fp->_ur;

        } else {

                n = fp->_p - fp->_bf._base;

                curoff -= n;

                n += fp->_r;

        }

        /*

         * If the target offset is within the current buffer,

         * simply adjust the pointers, clear EOF, undo ungetc(),

         * and return.  (If the buffer was modified, we have to

         * skip this; see fgetln.c.)

         */

        if ((fp->_flags & __SMOD) == 0 &&

            target >= curoff && target < curoff + n) {

                register int o = target - curoff;

                fp->_p = fp->_bf._base + o;

                fp->_r = n - o;

                if (HASUB(fp))

                        FREEUB(fp);

                fp->_flags &= ~__SEOF;

#ifdef _THREAD_SAFE

                _thread_funlockfile(fp);

#endif

                return (0);

        }

        /*

         * The place we want to get to is not within the current buffer,

         * but we can still be kind to the kernel copyout mechanism.

         * By aligning the file offset to a block boundary, we can let

         * the kernel use the VM hardware to map pages instead of

         * copying bytes laboriously.  Using a block boundary also

         * ensures that we only read one block, rather than two.

         */

        curoff = target & ~(fp->_blksize - 1);

        if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)

                goto dumb;

        fp->_r = 0;

        fp->_p = fp->_bf._base;

        if (HASUB(fp))

                FREEUB(fp);

        fp->_flags &= ~__SEOF;

        n = target - curoff;

        if (n) {

                if (__srefill(fp) || fp->_r < n)

                        goto dumb;

                fp->_p += n;

                fp->_r -= n;

        }

#ifdef _THREAD_SAFE

        _thread_funlockfile(fp);

#endif

        return (0);

        /*

         * We get here if we cannot optimise the seek ... just

         * do it.  Allow the seek function to change fp->_bf._base.

         */

dumb:

        if (__sflush(fp) ||

            (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) {

#ifdef _THREAD_SAFE

                _thread_funlockfile(fp);

#endif

                return (EOF);

        }

        /* success: clear EOF indicator and discard ungetc() data */

        if (HASUB(fp))

                FREEUB(fp);

        fp->_p = fp->_bf._base;

        fp->_r = 0;

        /* fp->_w = 0; */       /* unnecessary (I think...) */

        fp->_flags &= ~__SEOF;

#ifdef _THREAD_SAFE

        _thread_funlockfile(fp);

#endif

        return (0);

}