Date: | Mon, 3 Oct 2005 12:18:41 -0400 (EDT) |
From: | <kynn [...] panix.com> |
To: | bug-Math-Pari [...] rt.cpan.org |
Subject: | Incorrect conversion of unnormalized IEEE doubles |
severity=high
Math::Pari v2.010603
See below for other system details.
Math::Pari produces wrong results when it converts unnormalized IEEE
doubles to PARI reals. For example
print POSIX::DBL_MIN()/2
1.1125369292536e-308
...while
print Math::Pari::PARI( POSIX::DBL_MIN()/2 )
1.668805393880401037E-308
...which is actually POSIX::DBL_MIN*(3/4). This represents a relative
error of 50%, which is far from negligible.
It appears that Math::Pari::PARI is converting numbers of the form
POSIX::DBL_MIN()/2**$n
(where $n is a positive integer) into numbers of the form
POSIX::DBL_MIN()*((2**$n)-1)/(2**(-$n-1))
This problem occurs silently when an unnormalized IEEE double is
automatically promoted to a PARI real, as happens, for example, in
arithmetical operations involving both the unnormalized IEEE double
and a PARI real.
-----------------------------------------------------------------
---
Site configuration information for perl v5.8.6:
Configured by kynn at Tue Apr 12 12:24:11 EDT 2005.
Summary of my perl5 (revision 5 version 8 subversion 6) configuration:
Platform:
osname=linux, osvers=2.4.18-686-smp, archname=i686-linux-ld
uname='linux luna 2.4.18-686-smp #1 smp sun apr 14 12:07:19 est 2002 i686 unknown '
config_args=''
hint=recommended, useposix=true, d_sigaction=define
usethreads=undef use5005threads=undef useithreads=undef usemultiplicity=undef
useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
use64bitint=undef use64bitall=undef uselongdouble=define
usemymalloc=n, bincompat5005=undef
Compiler:
cc='cc', ccflags ='-fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
optimize='-O2',
cppflags='-fno-strict-aliasing -pipe -I/usr/local/include'
ccversion='', gccversion='2.95.4 20011002 (Debian prerelease)', gccosandvers=''
intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
ivtype='long', ivsize=4, nvtype='long double', nvsize=12, Off_t='off_t', lseeksize=8
alignbytes=4, prototype=define
Linker and Libraries:
ld='cc', ldflags =' -L/usr/local/lib'
libpth=/usr/local/lib /lib /usr/lib
libs=-lnsl -lgdbm -ldbm -ldb -ldl -lm -lcrypt -lutil -lc
perllibs=-lnsl -ldl -lm -lcrypt -lutil -lc
libc=/lib/libc-2.2.5.so, so=so, useshrplib=false, libperl=libperl.a
gnulibc_version='2.2.5'
Dynamic Linking:
dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'
Locally applied patches:
---
@INC for perl v5.8.6:
/home/kynn/local/lib/perl/my
/home/kynn/local/lib/perl/5.8.4
/home/kynn/local/lib/perl/5.6.1
/home/kynn/local/lib/perl5/5.8.6/i686-linux-ld
/home/kynn/local/lib/perl5/5.8.6
/home/kynn/local/lib/perl5/i686-linux-ld
/home/kynn/local/lib/perl5
/home/kynn/local/lib/perl5/5.8.6/i686-linux-ld
/home/kynn/local/lib/perl5/5.8.6
/home/kynn/local/lib/perl5/site_perl/5.8.6/i686-linux-ld
/home/kynn/local/lib/perl5/site_perl/5.8.6
/home/kynn/local/lib/perl5/site_perl
.
---
Environment for perl v5.8.6:
HOME=/home/kynn
LANG=C
LANGUAGE (unset)
LD_LIBRARY_PATH=/home/kynn/local/lib:/opt/java/jdk/lib/i386
LOGDIR (unset)
PATH=.:/home/kynn/local/bin:/home/kynn/local/usr/bin:/home/kynn/local/local/bin:/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin:/home/kynn/java/javacc/bin:/opt/java/jdk/bin:/usr/pbs/bin:/home/kynn/opt/ant/bin
PERL5LIB=/home/kynn/local/lib/perl/my:/home/kynn/local/lib/perl/5.8.4:/home/kynn/local/lib/perl/5.6.1:/home/kynn/local/lib/perl5
PERL5_CPANPLUS_CONFIG=/home/kynn/.cpanplus/config
PERL_BADLANG (unset)
SHELL=/usr/bin/zsh