seq(1): Consistently include 'last' for non-integers

The source of error is a rounded increment being too large and thus the loop
steps slightly past 'last'.  Perform a final comparison using the formatted
string values (truncated precision) to determine if we still need to print
the 'last' value.

PR:		217149
Submitted by:	Fernando Apesteguía <fernando.apesteguia AT gmail.com>,
		Yuri Pankov <yuripv AT icloud.com> (earlier version)
Reported by:	Martijn Dekker <mcdutchie AT hotmail.com>
Sponsored by:	Dell EMC Isilon

usr.bin/seq/Makefile

@@ -1,8 +1,13 @@
 #       $NetBSD: Makefile,v 1.3 2009/04/14 22:15:26 lukem Exp $
 # $FreeBSD$
 
+.include <src.opts.mk>
+
 PROG=	seq
 
 LIBADD=	m
 
+HAS_TESTS=
+SUBDIR.${MK_TESTS}+=	tests
+
 .include <bsd.prog.mk>

usr.bin/seq/seq.c

@@ -76,16 +76,19 @@ static char *unescape(char *);
 int
 main(int argc, char *argv[])
 {
-	int c = 0, errflg = 0;
-	int equalize = 0;
-	double first = 1.0;
-	double last = 0.0;
-	double incr = 0.0;
+	const char *sep, *term;
 	struct lconv *locale;
-	char *fmt = NULL;
-	const char *sep = "\n";
-	const char *term = NULL;
-	char pad = ZERO;
+	char pad, *fmt, *cur_print, *last_print;
+	double first, last, incr, last_shown_value, cur, step;
+	int c, errflg, equalize;
+
+	pad = ZERO;
+	fmt = NULL;
+	first = 1.0;
+	last = incr = last_shown_value = 0.0;
+	c = errflg = equalize = 0;
+	sep = "\n";
+	term = NULL;
 
 	/* Determine the locale's decimal point. */
 	locale = localeconv();
@@ -169,17 +172,32 @@ main(int argc, char *argv[])
 	} else
 		fmt = generate_format(first, incr, last, equalize, pad);
 
-	if (incr > 0) {
-		for (; first <= last; first += incr) {
-			printf(fmt, first);
-			fputs(sep, stdout);
-		}
-	} else {
-		for (; first >= last; first += incr) {
-			printf(fmt, first);
-			fputs(sep, stdout);
-		}
+	for (step = 1, cur = first; incr > 0 ? cur <= last : cur >= last;
+	    cur = first + incr * step++) {
+		printf(fmt, cur);
+		fputs(sep, stdout);
+		last_shown_value = cur;
 	}
+
+	/*
+	 * Did we miss the last value of the range in the loop above?
+	 *
+	 * We might have, so check if the printable version of the last
+	 * computed value ('cur') and desired 'last' value are equal.  If they
+	 * are equal after formatting truncation, but 'cur' and
+	 * 'last_shown_value' are not equal, it means the exit condition of the
+	 * loop held true due to a rounding error and we still need to print
+	 * 'last'.
+	 */
+	asprintf(&cur_print, fmt, cur);
+	asprintf(&last_print, fmt, last);
+	if (strcmp(cur_print, last_print) == 0 && cur != last_shown_value) {
+		fputs(last_print, stdout);
+		fputs(sep, stdout);
+	}
+	free(cur_print);
+	free(last_print);
+
 	if (term != NULL)
 		fputs(term, stdout);
 

usr.bin/seq/tests/Makefile

@@ -0,0 +1,7 @@
+# $FreeBSD$
+
+PACKAGE=	tests
+
+ATF_TESTS_SH=	seq_test
+
+.include <bsd.test.mk>

usr.bin/seq/tests/seq_test.sh

@@ -0,0 +1,40 @@
+# Copyright (c) 2018 Conrad Meyer <cem@FreeBSD.org>
+# All rights reserved.
+#
+# 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.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
+#
+# $FreeBSD$
+
+atf_test_case float_rounding
+float_rounding_head()
+{
+	atf_set "descr" "Check for correct termination in the face of floating point rounding"
+}
+float_rounding_body()
+{
+	atf_check -o inline:'1\n1.1\n1.2\n' seq 1 0.1 1.2
+}
+
+atf_init_test_cases()
+{
+	atf_add_test_case float_rounding
+}