http://d.hatena.ne.jp/hiratara/20121024/1351054828
https://rt.cpan.org/Public/Bug/Display.html?id=80350
In some environment, JSON::XS's floating point number decoder has an issue.
Here is code:
use v5.16.0; use JSON::XS; my $dat = decode_json( "[0.6]" )->[0]; say int ( 24 / $dat ); say int ( 24 / 0.6 );
Outputs:
39 40
Why??
The result of Devel::Peek::Dump($dat) is following:
SV = NV(0x26fc7d8) at 0x26ef7c8 REFCNT = 1 FLAGS = (PADMY,NOK,pNOK) NV = 0.6
Aghhh
Ah, 0.6 is floating point number. "NV = 0.6" is a rounded presentation. Use printf instead...
use v5.16.0; use JSON::XS; my $dat = decode_json( "[0.6]" )->[0]; use Devel::Peek; Dump($dat); printf("%.20f\n", $dat); printf("%.20f\n", 0.6);
Oh! Output is different!!
SV = NV(0x21c8820) at 0x21bb7c8 REFCNT = 1 FLAGS = (PADMY,NOK,pNOK) NV = 0.6 0.60000000000000008882 0.59999999999999997780
JSON::XS uses it's own json_atof() function for decoding floating point number. It's behavior is different between Perl5's floating point number decoder.
I seem the JSON dcoder's floating point number decoder should make same result with language processor's floating point number decoder.
I think JSON::XS needs to fix this issue.
I think JSON::PP and JSON::XS should return same value from same JSON data. Since these modules provides a wrapper interface named JSON.pm.
Current version of JSON::XS failed following test case in some environment:
use strict; use warnings; use 5.010000; use JSON::XS (); use JSON::PP (); use Test::More; my $xs = JSON::XS::decode_json("[0.6]")->[0]; my $pp = JSON::PP::decode_json("[0.6]")->[0]; ok($xs == $pp); diag sprintf("%.20f", $xs); diag sprintf("%.20f", $pp); done_testing;
Summary of my perl5 (revision 5 version 16 subversion 0) configuration:
Platform:
osname=linux, osvers=3.2.0-23-generic, archname=x86_64-linux
uname='linux www4071uf 3.2.0-23-generic #36-ubuntu smp tue apr 10 20:39:51 utc 2012 x86_64 x86_64 x86_64 gnulinux '
config_args='-d -Dprefix=/usr/local/perl/5.16.0/'
hint=recommended, useposix=true, d_sigaction=define
useithreads=undef, usemultiplicity=undef
useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
use64bitint=define, use64bitall=define, uselongdouble=undef
usemymalloc=n, bincompat5005=undef
Compiler:
cc='cc', ccflags ='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
optimize='-O2',
cppflags='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
ccversion='', gccversion='4.6.3', gccosandvers=''
intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
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 -L/usr/local/lib'
libpth=/usr/local/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib /usr/lib
libs=-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
perllibs=-lnsl -ldl -lm -lcrypt -lutil -lc
libc=, so=so, useshrplib=false, libperl=libperl.a
gnulibc_version='2.15'
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'