On 02/09/2025 13:11, ondra007....@seznam.cz wrote:
It looks like seq for integers bigger than 2^64 sometimes generate wrong
results. There are few examples of wrong output I have found:
$ seq 18446744073709551617 inf | head -3
18446744073709551616
18446744073709551617
18446744073709551618
$ seq 10000000000000000000000000000 inf | head -3
9999999999999999999731564544
9999999999999999999731564545
9999999999999999999731564546
We can improve for the above 2 cases anyway,
with something like the attached.
Large magnitude negative start values are still problematic.
cheers,
Padraig
From bf3c75911d1b50d557960943daaeb20a65f0140f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A1draig=20Brady?= <p...@draigbrady.com>
Date: Tue, 2 Sep 2025 16:35:52 +0100
Subject: [PATCH] seq: be more accurate with large integer start values
* src/seq.c (main): Use seq_fast() with large integer only
start values, by avoiding innacurate conversion to double.
* NEWS: Mention the improvement.
---
NEWS | 6 +++++-
src/seq.c | 8 ++++++--
2 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/NEWS b/NEWS
index dd8c1a4cf..e732e3ddd 100644
--- a/NEWS
+++ b/NEWS
@@ -116,11 +116,15 @@ GNU coreutils NEWS -*- outline -*-
tsort now accepts and ignores -w.
-** Performance improvements
+** Improvements
'factor' is now much faster at identifying large prime numbers,
and significantly faster on composite numbers greater than 2^128.
+ 'seq' is faster and more accurate with large integer start values.
+ Previously 'seq 18446744073709551617 inf | head -n3' would start
+ with the number before the user specified start value.
+
** Build-related
cksum was not compilable by Apple LLVM 10.0.0 x86-64, which
diff --git a/src/seq.c b/src/seq.c
index ea9b7d8a4..59de49798 100644
--- a/src/seq.c
+++ b/src/seq.c
@@ -628,6 +628,8 @@ main (int argc, char **argv)
usage (EXIT_FAILURE);
}
+ char const *user_start = n_args == 1 ? "1" : argv[optind];
+
/* If the following hold:
- no format string, [FIXME: relax this, eventually]
- integer start (or no start)
@@ -648,7 +650,7 @@ main (int argc, char **argv)
&& all_digits_p (argv[optind + 2])))
&& !equal_width && !format_str && strlen (separator) == 1)
{
- char const *s1 = n_args == 1 ? "1" : argv[optind];
+ char const *s1 = user_start;
char const *s2 = argv[optind + (n_args - 1)];
seq_fast (s1, s2, step.value);
}
@@ -683,7 +685,9 @@ main (int argc, char **argv)
{
char *s1;
char *s2;
- if (asprintf (&s1, "%0.Lf", first.value) < 0)
+ if (all_digits_p (user_start))
+ s1 = xstrdup (user_start);
+ else if (asprintf (&s1, "%0.Lf", first.value) < 0)
xalloc_die ();
if (! isfinite (last.value))
s2 = xstrdup ("inf"); /* Ensure "inf" is used. */
--
2.50.1
