"seq .1 .1" would mistakenly generate no output on FreeBSD 6.1

[Jim Meyering]

seq.c does this:

  for (i = 0; /* empty */; i++)
    {
      long double x = first + i * step;

      if (step < 0 ? x < last : last < x)

and for an invocation of "./seq .1 .1", it would print nothing
(surprise!) on FreeBSD 6.1.

Why?  Because with i == 0, it had last < x

  (gdb) p last
  $4 = 0.10000000000000000000135525271560688
  (gdb) p x
  $5 = 0.1000000000000000055511151231257827

I fixed it like this:
[and realized while typing this that the last < first conjunct,
 while right for this test case, was wrong for e.g., seq 1 -1 3.
 Another patch below. ]

diff --git a/ChangeLog b/ChangeLog
index 0e6c87a..d563ae9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2007-11-17  Jim Meyering  <address@hidden>
+
+       "seq .1 .1" would mistakenly generate no output on some systems
+       * NEWS: Say this.
+       * src/seq.c (print_numbers): Handle another floating point corner case.
+       This avoids failure of seq's eq-wid-7 test on FreeBSD 6.1.
+
 2007-11-16  Paul Eggert  <address@hidden>

        Port tests/rmdir/ignore away from GNU/Linux.
diff --git a/NEWS b/NEWS
index a8434c5..11efa75 100644
--- a/NEWS
+++ b/NEWS
@@ -142,6 +142,8 @@ GNU coreutils NEWS                                    -*- 
outline -*-
   seq would mistakenly reject some valid format strings containing %%,
   and would mistakenly accept some invalid ones. e.g., %g%% and %%g, resp.

+  "seq .1 .1" would mistakenly generate no output on some systems
+
   Obsolete sort usage with an invalid ordering-option character, e.g.,
   "env _POSIX2_VERSION=199209 sort +1x" no longer makes sort free an
   invalid pointer [introduced in coreutils-6.5]
diff --git a/src/seq.c b/src/seq.c
index d7d2521..77d5586 100644
--- a/src/seq.c
+++ b/src/seq.c
@@ -280,7 +280,13 @@ print_numbers (char const *fmt, struct layout layout,
              free (x_str);
            }

-         break;
+         /* With floating point arithmetic, we may well reach this point
+            with i == 0 and first == last.  E.g., ./seq .1 .1 on FreeBSD 6.1.
+            Hence the first conjunct: don't break out of this loop when
+            i == 0.  *unless* first and last themselves are out of order,
+            in which case we must print nothing, e.g. for ./seq -1  */
+         if (i || last < first)
+           break;
        }

       if (i)
--
1.5.3.5.726.g41a7a

diff --git a/ChangeLog b/ChangeLog
index d563ae9..6e6f713 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2007-11-17  Jim Meyering  <address@hidden>

+       Correct preceding patch.
+       * src/seq.c (print_numbers): Also handle first < last && step < 0.
+       * tests/misc/seq [empty-rev]: New test for this case.
+
        "seq .1 .1" would mistakenly generate no output on some systems
        * NEWS: Say this.
        * src/seq.c (print_numbers): Handle another floating point corner case.
diff --git a/src/seq.c b/src/seq.c
index 77d5586..eec5ed5 100644
--- a/src/seq.c
+++ b/src/seq.c
@@ -285,7 +285,7 @@ print_numbers (char const *fmt, struct layout layout,
             Hence the first conjunct: don't break out of this loop when
             i == 0.  *unless* first and last themselves are out of order,
             in which case we must print nothing, e.g. for ./seq -1  */
-         if (i || last < first)
+         if (i || (0 < step && last < first) || (step < 0 && first < last))
            break;
        }

diff --git a/tests/misc/seq b/tests/misc/seq
index 17c8f0c..3365d95 100755
--- a/tests/misc/seq
+++ b/tests/misc/seq
@@ -42,6 +42,7 @@ my @Tests =
   (
    ['onearg-1',        qw(10),         {OUT => [(1..10)]}],
    ['onearg-2',        qw(-1)],
+   ['empty-rev', qw(1 -1 3)],
    ['neg-1',   qw(-10 10 10),  {OUT => [qw(-10 0 10)]}],
    # ['neg-2', qw(-.1 .1 .11), {OUT => [qw(-0.1 0.0 0.1)]}],
    ['neg-3',   qw(1 -1 0),     {OUT => [qw(1 0)]}],
--
1.5.3.5.726.g41a7a