/*      $NetBSD: fread.c,v 1.27 2024/01/20 14:52:49 christos Exp $      */

/*-
 * 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. 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.
 */

#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
#if 0
static char sccsid[] = "@(#)fread.c     8.2 (Berkeley) 12/11/93";
#else
__RCSID("$NetBSD: fread.c,v 1.27 2024/01/20 14:52:49 christos Exp $");
#endif
#endif /* LIBC_SCCS and not lint */

#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include "reentrant.h"
#include "local.h"

#define MUL_NO_OVERFLOW (1UL << (sizeof(size_t) * 4))

size_t
fread(void *buf, size_t size, size_t count, FILE *fp)
{
        size_t resid;
        char *p;
        int r;
        size_t total;

        _DIAGASSERT(fp != NULL);

        /*
         * Extension:  Catch integer overflow
         */
        if ((size >= MUL_NO_OVERFLOW || count >= MUL_NO_OVERFLOW) &&
            size > 0 && count > SIZE_MAX / size) {
                errno = EOVERFLOW;
                fp->_flags |= __SERR;
                return (0);
        }

        /*
         * The ANSI standard requires a return value of 0 for a count
         * or a size of 0.  Whilst ANSI imposes no such requirements on
         * fwrite, the SUSv2 does.
         */
        if ((resid = count * size) == 0)
                return 0;

        _DIAGASSERT(buf != NULL);

        FLOCKFILE(fp);
        total = resid;
        p = buf;

        /*
         * If we're unbuffered we know that the buffer in fp is empty so
         * we can read directly into buf.  This is much faster than a
         * series of one byte reads into fp->_nbuf.
         */
        if ((fp->_flags & __SNBF) != 0) {
                while (resid > 0) {
                        /* set up the buffer */
                        fp->_bf._base = fp->_p = (unsigned char *)p;
                        fp->_bf._size = (int)resid;

                        if (__srefill(fp)) {
                                /* no more input: return partial result */
                                count = (total - resid) / size;
                                break;
                        }
                        p += fp->_r;
                        resid -= fp->_r;
                }

                /* restore the old buffer (see __smakebuf) */
                fp->_bf._base = fp->_p = fp->_nbuf;
                fp->_bf._size = 1;
                fp->_r = 0;

                FUNLOCKFILE(fp);
                return (count);
        }

        if (fp->_r <= 0) {
                /* Nothing to read on enter, refill the buffers. */
                goto refill;
        }

        while (resid > (size_t)(r = fp->_r)) {
                (void)memcpy(p, fp->_p, (size_t)r);
                fp->_p += r;
                /* fp->_r = 0 ... done in __srefill */
                p += r;
                resid -= r;
refill:
                if (__srefill(fp)) {
                        /* no more input: return partial result */
                        FUNLOCKFILE(fp);
                        return (total - resid) / size;
                }
        }
        (void)memcpy(p, fp->_p, resid);

        _DIAGASSERT(__type_fit(int, fp->_r - resid));
        fp->_r -= (int)resid;
        fp->_p += resid;
        FUNLOCKFILE(fp);
        return count;
}