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printf %a rounds incorrectly #15504

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p5pRT opened this issue Aug 10, 2016 · 4 comments

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commented Aug 10, 2016

Migrated from rt.perl.org#128890 (status was 'resolved')

Searchable as RT128890$

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commented Aug 10, 2016

From zefram@fysh.org

Created by zefram@fysh.org

$ perl -lwe 'printf "%a\n", 1.09375'
0x1.18p+0
$ perl -lwe 'printf "%.1a\n", 1.09375'
0x1.1p+0

The second output above is incorrect; it should be "0x1.2p+0". When
forced to round due to limited output precision, the rounding should be to
the nearest representable value, or, where equidistant between the nearest
two, to the one with the even least-significant digit. The tiebreaker
rule is not being respected here. Empirically, a nearest-or-toward-zero
rounding rule is being used, rather than nearest-or-even.

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
    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-f52 -Duselargefiles -Dusethreads -Uafs -Ud_csh -Uusesfio -Uusenm -Duseshrplib -Dusedevel -Uversiononly -Ui_db'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    use64bitint=define, use64bitall=define, uselongdouble=undef
    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='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=8, 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-f52/lib/5.24.0/x86_64-linux-thread-multi/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-f52/lib/site_perl/5.24.0/x86_64-linux-thread-multi
    /home/zefram/usr/perl/perl_install/perl-5.24.0-i64-f52/lib/site_perl/5.24.0
    /home/zefram/usr/perl/perl_install/perl-5.24.0-i64-f52/lib/5.24.0/x86_64-linux-thread-multi
    /home/zefram/usr/perl/perl_install/perl-5.24.0-i64-f52/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-f52/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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commented Aug 23, 2016

From @jhi

Marking resolved until proven otherwise.

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commented Aug 23, 2016

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

@p5pRT p5pRT closed this Aug 23, 2016
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commented Aug 23, 2016

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

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