Skip to content

printf %a mishandles exponent-crossing rounding with long double #15510

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom
Closed
p5pRT opened this issue Aug 12, 2016 · 5 comments
Closed

printf %a mishandles exponent-crossing rounding with long double #15510

p5pRT opened this issue Aug 12, 2016 · 5 comments
Labels
distro-Linux type-core

Comments

@p5pRT
Copy link

p5pRT commented Aug 12, 2016

Migrated from rt.perl.org#128909 (status was 'resolved')

Searchable as RT128909$
@p5pRT
Copy link
Author

p5pRT commented Aug 12, 2016

From [email protected]

Created by [email protected]

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.

Perl Info 

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

@p5pRT
Copy link
Author

p5pRT commented Aug 14, 2016

From @jhi

http​://perl5.git.perl.org/perl.git/commitdiff/9e67a8c1b21482ed5fada053dd462eb23320dc86 or thereabouts.

@p5pRT
Copy link
Author

p5pRT commented Aug 14, 2016

The RT System itself - Status changed from 'new' to 'open'

@p5pRT
Copy link
Author

p5pRT commented Aug 23, 2016

From @jhi

Marking resolved until proven otherwise.

@p5pRT
Copy link
Author

p5pRT commented Aug 23, 2016

@jhi - Status changed from 'open' to 'resolved'

@p5pRT p5pRT closed this as completed Aug 23, 2016
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Assignees
No one assigned
Labels
distro-Linux type-core
Projects
None yet
Milestone
No milestone
Development

No branches or pull requests
1 participant
@p5pRT