Along those lines, I'd suggest streamlining it even more and submitting it as a test file (i.e. use Test::More instead of print. For example:

use strict;
use warnings;
use Test::More tests => 3;
use bignum;

sub xe{
 $_[0]*log($_[0])+log(atan2(1,1)*8*$_[0])/2
  + 1/(12*$_[0]) - 1/(360*($_[0]**3)) + 1/(1260*($_[0]**5));
}

my ($m, $n, $r) = ( 2**96, 3*(10**6), 1*(10**6) );

my $e=exp(xe($m-$n)+xe($m-$r)-xe($m)-xe($m-$n-$r));

is( $e      , 1,    '$e should equal 1'     );
is( 1-$e    , 0,    '1-$e should equal 0'   );
is( 1-"$e"  , 0,    '1-"$e" should equal 0' );
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Gives:

1..3
ok 1 - $e should equal 1
not ok 2 - 1-$e should equal 0
#     Failed test (bigtest.pl at line 17)
#          got: '1'
#     expected: '0'
ok 3 - 1-"$e" should equal 0
# Looks like you failed 1 test of 3.
[download]

That's even easier for a module author to work with.

Good idea - thanks.

I eventually did find a way to simplify the math, and here's the test case I sent off:

#!perl
use strict;
use warnings;
use Test::More tests => 4;
use bignum;

my $lnev = -7 / (10**17);
my $ev=exp($lnev);

is( sprintf('%0.5f',$ev)     , '1.00000', '($ev) is approx. 1'     );
is( sprintf('%0.5f',1-$ev)   , '0.00000', '(1-$ev) is approx. 0'   );
is( sprintf('%0.5f',1-"$ev") , '0.00000', '(1-"$ev") is approx. 0' );

cmp_ok( $ev, '!=', 0, '$ev should not equal 0');
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Note that by futzing with the $lnev number, you can get this bug to disappear - for example, by changing the "7" to a "1".
--


@/=map{[/./g]}qw/.h_nJ Xapou cets krht ele_ r_ra/;
map{y/X_/\n /;print}map{pop@$_}@/for@/
[download]

Note that by futzing with the $lnev number, you can get this bug to disappear.

I'd add that to the test case. I find it helpful to show both working and non-working variations. Easier to drill in on what's happening.

-xdg

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