PR/56937 CVS commit: src

["Taylor R Campbell" <riastradh%netbsd.org@localhost>]

The following reply was made to PR lib/56937; it has been noted by GNATS.

From: "Taylor R Campbell" <riastradh%netbsd.org@localhost>
To: gnats-bugs%gnats.NetBSD.org@localhost
Cc: 
Subject: PR/56937 CVS commit: src
Date: Thu, 9 May 2024 12:24:24 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Thu May  9 12:24:24 UTC 2024
 
 Modified Files:
 	src/lib/libc/gdtoa: hdtoa.c
 	src/tests/lib/libc/stdio: t_printf.c
 
 Log Message:
 Revert various broken changes to printf %La (hldtoa).
 
 This reverts:
 
 hdtoa.c 1.12 (PR/56247: Greg A. Woods: printf("%La", LDBL_MIN) dumps core)
 hdtoa.c 1.11 (fix tyop)
 hdtoa.c 1.10 (Via enh at google dot com in tech-userlevel. Fix handling of
     EXT_FRAC{H,L}BITS (although we don't need to since we don't have them).)
 
 The underlying motivation for this change was that when ld128 is
 decomposed into 4x32 words, this hldtoa logic is broken.
 
 But we don't decompose ld128 into 4x32 words; we decompose it into
 6x64 words.
 
 And the change, which was supposed to be a noop in our case of 2x64
 words (or similar for x87 80-bit floating-point), broke it to the
 point of causing buffer overruns (PR 56247) which when worked around
 led to just incorrect output output (PR 56937).
 
 If we want to make the #ifdefs for 4x32 words work, that's fine, but
 we absolutely must have automatic test cases to detect this kind of
 regression because %La formatting is extremely important for
 diagnosing details of floating-point data since it doesn't involve
 rounding in binary formats.  For now I've added some trivial tests;
 there is a more extensive test suite inside gdtoa that we need to
 wire up before anyone tries any other shenanigans in this code.
 
 PR lib/56937: printf(3) long double %a formatting is broken
 
 
 To generate a diff of this commit:
 cvs rdiff -u -r1.12 -r1.13 src/lib/libc/gdtoa/hdtoa.c
 cvs rdiff -u -r1.14 -r1.15 src/tests/lib/libc/stdio/t_printf.c
 
 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.