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rcsid[] and sccsid[] and copyright[] are essentially unmaintained (and
unmaintainable).  these days, people use source.  these id's do not provide
any benefit, and do hurt the small install media
(the 33,000 line diff is essentially mechanical)
ok with the idea millert, ok dms

/*	$OpenBSD: reverse.c,v 1.19 2009/10/27 23:59:44 deraadt Exp $	*/
/*	$NetBSD: reverse.c,v 1.6 1994/11/23 07:42:10 jtc Exp $	*/

/*-
 * Copyright (c) 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Edward Sze-Tyan Wang.
 *
 * 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/stat.h>

#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include "extern.h"

static void r_buf(FILE *);
static int r_reg(FILE *, enum STYLE, off_t, struct stat *);

#define COPYCHAR(fp, ch)				\
	do {						\
		if ((ch = getc(fp)) == EOF) {		\
			ierr();				\
			return (0);			\
		}					\
		if (putchar(ch) == EOF) {		\
			oerr();				\
			return (0);			\
		}					\
	} while (0)

/*
 * reverse -- display input in reverse order by line.
 *
 * There are six separate cases for this -- regular and non-regular
 * files by bytes, lines or the whole file.
 *
 * BYTES	display N bytes
 *	REG	reverse scan and display the lines
 *	NOREG	cyclically read characters into a wrap-around buffer
 *
 * LINES	display N lines
 *	REG	reverse scan and display the lines
 *	NOREG	cyclically read lines into a wrap-around array of buffers
 *
 * FILE		display the entire file
 *	REG	reverse scan and display the lines
 *	NOREG	cyclically read input into a linked list of buffers
 */
void
reverse(FILE *fp, enum STYLE style, off_t off, struct stat *sbp)
{
	if (style != REVERSE && off == 0)
		return;

	if (!S_ISREG(sbp->st_mode) || r_reg(fp, style, off, sbp) != 0)
		switch(style) {
		case FBYTES:
		case RBYTES:
			(void)bytes(fp, off);
			break;
		case FLINES:
		case RLINES:
			(void)lines(fp, off);
			break;
		case REVERSE:
			r_buf(fp);
			break;
		}
}

/*
 * r_reg -- display a regular file in reverse order by line.
 */
static int
r_reg(FILE *fp, enum STYLE style, off_t off, struct stat *sbp)
{
	off_t start, pos, end;
	int ch;

	end = sbp->st_size;
	if (end == 0)
		return (0);

	/* Position before char, ignore last char whether newline or not */
	pos = end-2;
	ch = EOF;
	start = 0;

	if (style == RBYTES && off < end)
		start = end - off;

	for (; pos >= start; pos--) {
		/* A seek per char isn't a problem with a smart stdio */
		if (fseeko(fp, pos, SEEK_SET) != 0) {
			ierr();
			return (0);
		}
		if ((ch = getc(fp)) == '\n') {
			while (--end > pos) 
				COPYCHAR(fp, ch);
			end++;
			if (style == RLINES && --off == 0)
				break;
		}
		else if (ch == EOF) {
			ierr();
			return (0);
		}
	}
	if (pos < start) {
		if (ch != EOF && ungetc(ch, fp) == EOF) {
			ierr();
			return (0);
		}
		while (--end >= start)
			COPYCHAR(fp, ch);
	}
	return (0);
}

typedef struct bf {
	struct bf *next;
	struct bf *prev;
	size_t len;
	char *l;
} BF;

/*
 * r_buf -- display a non-regular file in reverse order by line.
 *
 * This is the function that saves the entire input, storing the data in a
 * doubly linked list of buffers and then displays them in reverse order.
 * It has the usual nastiness of trying to find the newlines, as there's no
 * guarantee that a newline occurs anywhere in the file, let alone in any
 * particular buffer.  If we run out of memory, input is discarded (and the
 * user warned).
 */
static void
r_buf(FILE *fp)
{
	BF *mark, *tr, *tl = NULL;
	int ch;
	size_t len, llen;
	char *p;
	off_t enomem;

#define	BSZ	(128 * 1024)
	for (mark = NULL, enomem = 0;;) {
		/*
		 * Allocate a new block and link it into place in a doubly
		 * linked list.  If out of memory, toss the LRU block and
		 * keep going.
		 */
		if (enomem || (tl = malloc(sizeof(BF))) == NULL ||
		    (tl->l = malloc(BSZ)) == NULL) {
			if (!mark)
				err(1, NULL);
			tl = enomem ? tl->next : mark;
			enomem += tl->len;
		} else if (mark) {
			tl->next = mark;
			tl->prev = mark->prev;
			mark->prev->next = tl;
			mark->prev = tl;
		} else {
			mark = tl;
			mark->next = mark->prev = mark;
		}

		if (!enomem)
			tl->len = 0;

		/* Fill the block with input data. */
		for (p = tl->l, len = 0;
		    len < BSZ && (ch = getc(fp)) != EOF; ++len)
			*p++ = ch;

		/*
		 * If no input data for this block and we tossed some data,
		 * recover it.
		 */
		if (!len) {
			if (enomem)
				enomem -= tl->len;
			tl = tl->prev;
			break;
		}

		tl->len = len;
		if (ch == EOF)
			break;
	}

	if (enomem) {
		(void)fprintf(stderr,
		    "tail: warning: %lld bytes discarded\n", (long long)enomem);
		rval = 1;
	}

	/*
	 * Step through the blocks in the reverse order read.  The last char
	 * is special, ignore whether newline or not.
	 */
	for (mark = tl;;) {
		for (p = tl->l + (len = tl->len) - 1, llen = 0; len--;
		    --p, ++llen)
			if (*p == '\n') {
				if (llen) {
					WR(p + 1, llen);
					llen = 0;
				}
				if (tl == mark)
					continue;
				for (tr = tl->next; tr->len; tr = tr->next) {
					WR(tr->l, tr->len);
					tr->len = 0;
					if (tr == mark)
						break;
				}
			}
		tl->len = llen;
		if ((tl = tl->prev) == mark)
			break;
	}
	tl = tl->next;
	if (tl->len) {
		WR(tl->l, tl->len);
		tl->len = 0;
	}
	while ((tl = tl->next)->len) {
		WR(tl->l, tl->len);
		tl->len = 0;
	}
}