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Report information
Id: 128909
Status: resolved
Priority: 0/
Queue: perl5

Owner: Nobody
Requestors: zefram [at] fysh.org
Cc:
AdminCc:

Operating System: Linux
PatchStatus: (no value)
Severity: low
Type: core
Perl Version: 5.24.0
Fixed In: (no value)



Date: Fri, 12 Aug 2016 12:51:35 +0100
Subject: printf %a mishandles exponent-crossing rounding with long double
To: perlbug [...] perl.org
CC: zefram [...] fysh.org
From: zefram [...] fysh.org
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This is a bug report for perl from zefram@fysh.org, generated with the help of perlbug 1.40 running under perl 5.24.0. ----------------------------------------------------------------- [Please describe your issue here] On an x86 long-double build (63 fractional significand bits): $ perl -lwe 'printf "%a\n", 1.9999999999999999999' 0xf.fffffffffffffffp-3 $ perl -lwe 'printf "%.3a\n", 1.9999999999999999999' 0x10.000p-3 The latter output is wrong. It is numerically correct, but (per the C spec) it is not permitted to have more than one hex digit before the radix point. It is necessary for the output to be expressed with a higher exponent, such as "0x1.000p+1". FWIW, glibc uses the same digit alignment for this long double type, so gives identical output for the unrounded case, and gives "0x1.000p+1" for the rounded case. [Please do not change anything below this line] ----------------------------------------------------------------- --- Flags: category=core severity=low --- Site configuration information for perl 5.24.0: Configured by zefram at Mon May 9 19:42:55 BST 2016. Summary of my perl5 (revision 5 version 24 subversion 0) configuration: Platform: osname=linux, osvers=3.16.0-4-amd64, archname=x86_64-linux-thread-multi-ld uname='linux barba.rous.org 3.16.0-4-amd64 #1 smp debian 3.16.7-ckt11-1+deb8u6 (2015-11-09) x86_64 gnulinux ' config_args='-des -Dprefix=/home/zefram/usr/perl/perl_install/perl-5.24.0-i64-f63 -Duselargefiles -Dusethreads -Uafs -Ud_csh -Uusesfio -Uusenm -Duseshrplib -Dusedevel -Uversiononly -Ui_db -Duselongdouble' hint=recommended, useposix=true, d_sigaction=define useithreads=define, usemultiplicity=define use64bitint=define, use64bitall=define, uselongdouble=define usemymalloc=n, bincompat5005=undef Compiler: cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2', optimize='-O2', cppflags='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include' ccversion='', gccversion='4.9.2', gccosandvers='' intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678, doublekind=3 d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16, longdblkind=3 ivtype='long', ivsize=8, nvtype='long double', nvsize=16, Off_t='off_t', lseeksize=8 alignbytes=16, prototype=define Linker and Libraries: ld='cc', ldflags =' -fstack-protector-strong -L/usr/local/lib' libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/4.9/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib libs=-lpthread -lnsl -ldb -ldl -lm -lcrypt -lutil -lc perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc libc=libc-2.19.so, so=so, useshrplib=true, libperl=libperl.so gnulibc_version='2.19' Dynamic Linking: dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E -Wl,-rpath,/home/zefram/usr/perl/perl_install/perl-5.24.0-i64-f63/lib/5.24.0/x86_64-linux-thread-multi-ld/CORE' cccdlflags='-fPIC', lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong' --- @INC for perl 5.24.0: /home/zefram/usr/perl/perl_install/perl-5.24.0-i64-f63/lib/site_perl/5.24.0/x86_64-linux-thread-multi-ld /home/zefram/usr/perl/perl_install/perl-5.24.0-i64-f63/lib/site_perl/5.24.0 /home/zefram/usr/perl/perl_install/perl-5.24.0-i64-f63/lib/5.24.0/x86_64-linux-thread-multi-ld /home/zefram/usr/perl/perl_install/perl-5.24.0-i64-f63/lib/5.24.0 . --- Environment for perl 5.24.0: HOME=/home/zefram LANG (unset) LANGUAGE (unset) LD_LIBRARY_PATH (unset) LOGDIR (unset) PATH=/home/zefram/usr/perl/perl_install/perl-5.24.0-i64-f63/bin:/home/zefram/usr/perl/util:/home/zefram/pub/x86_64-unknown-linux-gnu/bin:/home/zefram/pub/common/bin:/usr/bin:/bin:/usr/local/bin:/usr/games PERL_BADLANG (unset) SHELL=/usr/bin/zsh
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