From 2f56f5a42033dc6db15d8963e54566f01fa0d61d Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sun, 1 May 2022 22:46:21 -0700
Subject: [PATCH] sort: fix sort -g infloop again

Problem reported by Giulio Genovese (Bug#55212).
* src/sort.c (nan_compare): To compare NaNs, simply printf+strcmp.
This avoids the problem of padding bits and unspecified behavior.
Args are now long double instead of char *; caller changed.

Reference:https://github.com/coreutils/coreutils/commit/2f56f5a42033dc6db15d8963e54566f01fa0d61d
Conflict: NEWS Context adaptation

---
 NEWS       |  6 ++++++
 src/sort.c | 21 ++++++---------------
 2 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/NEWS b/NEWS
index 3e44c0c..fc8ff16 100644
--- a/NEWS
+++ b/NEWS
@@ -4,6 +4,12 @@ GNU coreutils NEWS                                    -*- outline -*-
 
 ** Bug fixes
 
+  'sort -g' no longer infloops when given multiple NaNs on platforms
+  like x86-64 where 'long double' has padding bits in memory.
+  Although the fix alters sort -g's NaN ordering, that ordering has
+  long been documented to be platform-dependent.
+  [bug introduced 1999-05-02 and only partly fixed in coreutils-8.14]
+
   cp now copies /dev/fd/N correctly on platforms like Solaris where
   it is a character-special file whose minor device number is N.
   [bug introduced in fileutils-4.1.6]
diff --git a/src/sort.c b/src/sort.c
index 8e1533e..5b4342f 100644
--- a/src/sort.c
+++ b/src/sort.c
@@ -2360,22 +2360,13 @@ numcompare_mb (const char *a, const char *b)
 }
 #endif /* HAV_EMBRTOWC */
 
-/* Work around a problem whereby the long double value returned by glibc's
-   strtold ("NaN", ...) contains uninitialized bits: clear all bytes of
-   A and B before calling strtold.  FIXME: remove this function if
-   gnulib guarantees that strtold's result is always well defined.  */
 static int
-nan_compare (char const *sa, char const *sb)
+nan_compare (long double a, long double b)
 {
-  long double a;
-  memset (&a, 0, sizeof a);
-  a = strtold (sa, NULL);
-
-  long double b;
-  memset (&b, 0, sizeof b);
-  b = strtold (sb, NULL);
-
-  return memcmp (&a, &b, sizeof a);
+  char buf[2][sizeof "-nan()" + CHAR_BIT * sizeof a];
+  snprintf (buf[0], sizeof buf[0], "%Lf", a);
+  snprintf (buf[1], sizeof buf[1], "%Lf", b);
+  return strcmp (buf[0], buf[1]);
 }
 
 static int
@@ -2403,7 +2394,7 @@ general_numcompare (char const *sa, char const *sb)
           : a == b ? 0
           : b == b ? -1
           : a == a ? 1
-          : nan_compare (sa, sb));
+          : nan_compare (a, b));
 }
 
 /* Return an integer in 1..12 of the month name MONTH.
-- 
2.27.0

