This issue is found with perl-5.32.0, all the way back to perl-5.8.9 (AFAICT), there being no such issue on perl-5.6.2
Same problem exists on my Debian Wheezy system, but Windows (Windows 7) and FreeBSD (freebsd-12.0) are fine.
I'm interested in fixing this - I would appreciate any hints on whereabouts in the perl source I should start looking.
For this report, I'll stick to version 5.32.0 and Ubuntu-18.04.
Description
"%.${digits}g" formatting is broken for $digits > 17, $Config{nvsize} == 8.
A quick check indicates that this type of issue does NOT occur with -Duselongdouble and -Dusequadmath builds of perl.
Steps to Reproduce
For example:
$ perl -le 'printf "%.54g\n", 0.3
0.29999999999999999
$ perl -le 'printf "%.53e\n", 0.3;'
2.99999999999999988897769753748434595763683319091796875e-01
Expected behavior
As you can see, the "%.53e" formatting is fine and produces the correct result.
I expected the "%.54g" formatting to produce:
0.299999999999999988897769753748434595763683319091796875
but, either my expectation is way out of line, or the %g formatting is severely crippled.
The significance of the correct output is that it exactly represents (as a base 10 number) the actual value held by the double 0.3.
The "%.54g" formatting works fine in C, using the compiler that built this perl-5.32.0.
Given that the capability for such extended formatting already exists, I'm hopeful that it can be provided to "%g" without too much difficulty.
Cheers,
Rob
Perl configuration
# perl -V output goes here
Summary of my perl5 (revision 5 version 32 subversion 0) configuration:
Platform:
osname=linux
osvers=4.15.0-106-generic
archname=x86_64-linux
uname='linux sisyphus5-desktop 4.15.0-106-generic #107-ubuntu smp thu jun 4 11:27:52 utc 2020 x86_64 x86_64 x86_64 gnulinux '
config_args='-des -Duse64bitall -Dprefix=/home/sisyphus/perl-5.32.0-d'
hint=recommended
useposix=true
d_sigaction=define
useithreads=undef
usemultiplicity=undef
use64bitint=define
use64bitall=define
uselongdouble=undef
usemymalloc=n
default_inc_excludes_dot=define
bincompat5005=undef
Compiler:
cc='cc'
ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64'
optimize='-O2'
cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
ccversion=''
gccversion='7.5.0'
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/7/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 -ldl -lm -lcrypt -lutil -lc
perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
libc=libc-2.27.so
so=so
useshrplib=false
libperl=libperl.a
gnulibc_version='2.27'
Dynamic Linking:
dlsrc=dl_dlopen.xs
dlext=so
d_dlsymun=undef
ccdlflags='-Wl,-E'
cccdlflags='-fPIC'
lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'
Characteristics of this binary (from libperl):
Compile-time options:
HAS_TIMES
PERLIO_LAYERS
PERL_COPY_ON_WRITE
PERL_DONT_CREATE_GVSV
PERL_MALLOC_WRAP
PERL_OP_PARENT
PERL_PRESERVE_IVUV
USE_64_BIT_ALL
USE_64_BIT_INT
USE_LARGE_FILES
USE_LOCALE
USE_LOCALE_COLLATE
USE_LOCALE_CTYPE
USE_LOCALE_NUMERIC
USE_LOCALE_TIME
USE_PERLIO
USE_PERL_ATOF
Built under linux
Compiled at Jun 25 2020 19:42:19
@inc:
/home/sisyphus/perl-5.32.0-d/lib/site_perl/5.32.0/x86_64-linux
/home/sisyphus/perl-5.32.0-d/lib/site_perl/5.32.0
/home/sisyphus/perl-5.32.0-d/lib/5.32.0/x86_64-linux
/home/sisyphus/perl-5.32.0-d/lib/5.32.0
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