in reply to Re^2: Portability of floor(log(N))

in thread Portability of floor(log(N))

*Thank you for the suggestions.*

I think they were completely irrelevant to the problem you're facing.

Silly me didn't think to actually check what the

**correct**calculation of

`floor( log($num) / log(1000) )`should yield under 'long double' (64-bit) precision.

When I do check, I find that the correct answer is -12.

The error is in your test script ... either that, or in Math::MPFR:

This indicates that when the floating point precision is 64 bits, the correct floor() result is -12.use strict; use warnings; use Math::MPFR qw(:mpfr); # Set precision for extended # precision 'long double' Rmpfr_set_default_prec(64); my $num = Math::MPFR->new('1e-33'); my $thou = Math::MPFR->new('1000'); # Convert $num & $thou to their # respective log() Rmpfr_log($num, $num, MPFR_RNDN); Rmpfr_log($thou, $thou, MPFR_RNDN); print $num / $thou; # prints -1.10000000000000000009e1

And, IIUC, the test script should accept '1000e-36' as correct when NV precision is 64 bits (as is the case with those 2 FAIL reports).

Interestingly, with full quad precision of 113 bits, the calculation reverts to returning -11.

Cheers,

Rob

In Section
Seekers of Perl Wisdom