PR/56937 CVS commit: [netbsd-9] src/tests/lib/libc/stdio

[gnats-admin%netbsd.org@localhost]

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

From: "Martin Husemann" <martin%netbsd.org@localhost>
To: gnats-bugs%gnats.NetBSD.org@localhost
Cc: 
Subject: PR/56937 CVS commit: [netbsd-9] src/tests/lib/libc/stdio
Date: Thu, 22 Aug 2024 19:53:56 +0000

 Module Name:	src
 Committed By:	martin
 Date:		Thu Aug 22 19:53:56 UTC 2024
 
 Modified Files:
 	src/tests/lib/libc/stdio [netbsd-9]: t_printf.c
 
 Log Message:
 Pull up following revision(s) (requested by riastradh in ticket #1866):
 
 	tests/lib/libc/stdio/t_printf.c: revision 1.17
 	tests/lib/libc/stdio/t_printf.c: revision 1.18
 	tests/lib/libc/stdio/t_printf.c: revision 1.11
 	tests/lib/libc/stdio/t_printf.c: revision 1.12
 	tests/lib/libc/stdio/t_printf.c: revision 1.13
 	tests/lib/libc/stdio/t_printf.c: revision 1.14
 	tests/lib/libc/stdio/t_printf.c: revision 1.15
 	tests/lib/libc/stdio/t_printf.c: revision 1.16
 	(all via patch)
 
 tests/lib/libc/stdio/t_printf: Add a couple simple %La tests.
 
 PR lib/56937: printf(3) long double %a formatting is broken
 tests/lib/libc/stdio/t_printf: Fix %La test.
 0xa.99ap+0 is closer to (long double)10.6 in x86 ld80 and in
 binary128 (and possibly more formats, haven't verified).
 tests/lib/libc/stdio/t_printf: Fix %a test the same way.
 tests/lib/libc/stdio/t_printf: Add another %La test.
 
 This one was adapted from the screw case shown in
 https://mail-index.netbsd.org/tech-userlevel/2020/04/11/msg012329.html
 which wasn't broken in our libc, but which nevertheless prompted us
 to commit a wrong and apparently untested patch that has rendered
 printf %La broken for the last four years, which is a little
 embarrassing.  (The part of that patch that led to a buffer overrun
 has been worked around, so now the output is just incorrect.)
 
 PR lib/56937: printf(3) long double %a formatting is broken
 tests/lib/libc/stdio/t_printf: Fix another rounding error.
 Noted by kre.
 
 This doesn't break a passing test or fix a failed test, at least on
 x86 -- our printf produces `0x1.533p+3' for the double case and
 `0xa.99ap+0' for the long double case.  But of the hexadecimal number
 literals that that start with 0x5 having three hexadigits to the
 right of the fractional point, 0x5.4cdp+1 closest to the IEEE 754
 binary64, VAX D, x86 extended precision, and IEEE 754 binary128
 floating-point numbers closest to 10.6.
 
 The reason is that the number 10.6 (or the nearest floating-point
 number in any format with enough precision) is:
 101.0100 1100 1100|1100... * 2^1 = 0x5.4cc|c...p+1
 
 If we round at the vertical bar to the _nearest_ output with three
 hexadigits of precision, the result is:
 101.0100 1100 1101 * 2^1 = 0x5.4cdp+1
 
 tests/lib/libc/stdio/t_printf: Fix typo in ld128 case.
 printf %La does not write the `L' suffix.
 
 tests/lib/libc/stdio/t_printf: Fix sign error in ld128 case.
 Also link back to where the test case came from.
 
 
 To generate a diff of this commit:
 cvs rdiff -u -r1.8.34.1 -r1.8.34.2 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.