Re: standards/59332: awk handling of NaN comparisons

["RVP via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR standards/59332; it has been noted by GNATS.

From: RVP <rvp%SDF.ORG@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: kre%netbsd.org@localhost
Subject: Re: standards/59332: awk handling of NaN comparisons
Date: Mon, 21 Apr 2025 07:19:01 +0000 (UTC)

 On Sun, 20 Apr 2025, dholland%NetBSD.org@localhost wrote:
 
 > awk recognizes "NaN":
 >
 >   % echo foo | awk '{ x = "NaN" + 1; print x; }'
 >   nan
 >
 
 You have an old awk. Christos updated it last year:
 
 ```
 $ fgrep awk /usr/src/doc/CHANGES
          awk(1): Import 20240817 [christos 20240817]
 $
 ```
 
 which now gives:
 
 ```
 $ awk --version
 awk version 20240728
 
 ;; note that this must be exactly one of: `+nan', `-nan', `+inf' or `-inf'
 ;; (case-insensitive) to be recognized.
 ;;
 $ awk 'BEGIN { x = "+NaN" + 0; print x; print (x == x); print (x != x); print (x <= x); }'
 +nan
 0
 1
 0
 
 $
 ```
 
 > but NaNs are supposed to be unequal to themselves:
 >
 >   % echo foo | awk '{ x = "NaN" + 1; print (x == x); }'
 >   1
 >   % echo foo | awk '{ x = "NaN" + 1; print (x != x); }'
 >   0
 >   % echo foo | awk '{ x = "NaN" + 1; print (x <= x); }'
 >   1
 >
 
 I'm not so sure that that's invalid from what POSIX[1] seems to say (CC: kre@):
 
 ```
 Historical implementations of awk did not support floating-point
 infinities and NaNs in numeric strings; e.g., "-INF" and "NaN".
 However, implementations that use the atof() or strtod() functions
 to do the conversion picked up support for these values if they
 used a ISO/IEC 9899:1999 standard version of the function instead
 of a ISO/IEC 9899:1990 standard version. Due to an oversight, the
 2001 through 2004 editions of this standard did not allow support
 for infinities and NaNs, but in this revision support is allowed
 (but not required). This is a silent change to the behavior of awk
 programs; for example, in the POSIX locale the expression:
 
 ("-INF" + 0 < 0)
 
 formerly had the value 0 because "-INF" converted to 0, but now it
 may have the value 0 or 1.
 ```
 [1]: https://pubs.opengroup.org/onlinepubs/9799919799.2024edition/utilities/awk.html
 
 
 Anyway, the latest GAWK prints:
 
 ```
 $ /tmp/G/bin/gawk --version
 GNU Awk 5.3.2, API 4.0
 Copyright (C) 1989, 1991-2025 Free Software Foundation.
 
 This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation; either version 3 of the License, or
 (at your option) any later version.
 
 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.
 
 You should have received a copy of the GNU General Public License
 along with this program. If not, see http://www.gnu.org/licenses/.
 
 ;; GAWK accepts plain `NaN' only if you pass `--posix'.
 ;;
 $ /tmp/G/bin/gawk 'BEGIN { x = "+NaN" + 0; print x; print (x == x); print (x != x); print (x <= x); }'
 +nan
 0
 1
 0
 
 $
 ```
 
 while the latest MAWK prints:
 
 ```
 $ /tmp/M/bin/mawk --version
 mawk 1.3.4 20250131
 Copyright 2008-2024,2025, Thomas E. Dickey
 Copyright 1991-1996,2014, Michael D. Brennan
 
 random-funcs:       srandom/random
 regex-funcs:        internal
 
 compiled limits:
 sprintf buffer      8192
 maximum-integer     9223372036854775808
 
 ;; MAWK needs `-Wposix' to recognize any NaNs, then coerces them all to +NaN,
 ;; and then gets it all wrong anyway. (It also accepts `nancy' as +NaN.)
 ;;
 $ /tmp/M/bin/mawk -Wposix 'BEGIN { x = "+NaN" + 0; print x; print (x == x); print (x != x); print (x <= x); }'
 +nan
 1
 0
 1
 
 $
 ```
 
 -RVP