Yes, they return the same value. And here's the output of perl -V : Summary of my perl5 (revision 5 version 30 subversion 0) configuration: Platform: osname=solaris osvers=2.11 archname=i86pc-solaris uname='sunos openindiana 5.11 illumos-ffec1fd1b2 i86pc i386 i86pc ' config_args='' hint=recommended useposix=true d_sigaction=define useithreads=undef usemultiplicity=undef use64bitint=undef use64bitall=undef uselongdouble=undef usemymalloc=n default_inc_excludes_dot=define bincompat5005=undef Compiler: cc='gcc' ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/gnu/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2 -DPERL_USE_SAFE_PUTENV' optimize='-O' cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/gnu/include' ccversion='' gccversion='6.5.0' gccosandvers='' intsize=4 longsize=4 ptrsize=4 doublesize=8 byteorder=1234 doublekind=3 d_longlong=define longlongsize=8 d_longdbl=define longdblsize=12 longdblkind=3 ivtype='long' ivsize=4 nvtype='double' nvsize=8 Off_t='off_t' lseeksize=8 alignbytes=4 prototype=define Linker and Libraries: ld='gcc' ldflags =' -fstack-protector-strong -L/usr/gnu/lib ' libpth=/usr/gcc/6/lib /usr/lib /usr/gnu/lib /usr/ccs/lib libs=-lpthread -lsocket -lnsl -lgdbm -ldb -ldl -lm -lc perllibs=-lpthread -lsocket -lnsl -ldl -lm -lc libc=/lib/libc.so so=so useshrplib=true libperl=libperl.so gnulibc_version='' Dynamic Linking: dlsrc=dl_dlopen.xs dlext=so d_dlsymun=undef ccdlflags=' -R /opt/lib/perl5/5.30.0/i86pc-solaris/CORE' cccdlflags='-fPIC' lddlflags='-shared -L/usr/gnu/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 PERL_USE_SAFE_PUTENV USE_LARGE_FILES USE_LOCALE USE_LOCALE_COLLATE USE_LOCALE_CTYPE USE_LOCALE_NUMERIC USE_LOCALE_TIME USE_PERLIO USE_PERL_ATOF Built under solaris Compiled at Jun 3 2019 18:02:06 @INC: /opt/lib/perl5/site_perl/5.30.0/i86pc-solaris /opt/lib/perl5/site_perl/5.30.0 /opt/lib/perl5/5.30.0/i86pc-solaris /opt/lib/perl5/5.30.0 On Tue, Jun 4, 2019 at 4:16 AM sisyphus@cpan.org via RT <perlbug-followup@perl.org> wrote: > > > That is, configure and build like this: > > > > ##### > > sh ./Configure -des -Dusedevel -Duse64bitall && make test_prep > > ##### > > > > ... and then run: > > > > ##### > > cd t;./perl harness -v ../ext/POSIX/t/math.t;cd - > > ##### > > To the OP: > If you're able to do that, and it fixes the problem, could you also provide the 'perl -V' output for this new build. > > Also (as a stab in the dark), on your first build, could you confirm that tanh(-1) and tanh(-1.0) are both returning the same incorrect value of 0.761594155955765. > The value should be -0.761594155955765. > > Cheers, > RobThread Next