From 2f56f5a42033dc6db15d8963e54566f01fa0d61d Mon Sep 17 00:00:00 2001
From: Paul Eggert <[email protected]>
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.
---
 src/sort.c | 21 ++++++---------------
 1 files changed, 6 insertions(+), 15 deletions(-)

diff --git a/src/sort.c b/src/sort.c
index 3b775d6bb..b2a465cf5 100644
--- a/src/sort.c
+++ b/src/sort.c
@@ -2359,22 +2359,13 @@ numcompare (char const *a, char const *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
@@ -2402,7 +2393,7 @@ 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