I'm sure you've moved beyond this... but for future searchers:

While trying to implement some ULP-manipulating routines in my Data::IEEE754::Tools development (which I used to call Expand.pm), I was googling to fix a bug, and was led to Data::Float, which actually has most of the tools I was trying to implement in my module. Using that CPAN module, I was able to write a sub which found the ULP for any finite value (normal or denormal); it returns INF or NAN when one of those was passed.

use warnings;
use strict;
use feature qw/say/;
use Data::Float qw/pow2 float_parts float_hex significand_bits
    min_normal min_normal_exp min_finite min_finite_exp max_finite
    pos_zero neg_zero pos_infinity neg_infinity nan
    float_is_zero float_is_finite/;

sub find_ulp($) {
    my $nv = shift;
    my $vh = float_hex($nv);

    if(!float_is_finite($nv)) {  # INF or NAN
        say "ulp($nv:$vh) = $nv:$vh";
        return $nv;
    }

    my $e  = float_is_zero($nv) ? (min_finite_exp) : ( (float_parts($n
+v))[1] - significand_bits );
    my $uv = pow2($e);
    my $uh = float_hex($uv);

    say "ulp($nv:$vh) = $uv:$uh";
    return $uv;
}

find_ulp($_) foreach (2.0, 1.0, 0.5, 0.16, max_finite, min_normal, min
+_normal/2., min_finite, pos_zero, neg_zero , pos_infinity , neg_infin
+ity , nan);

__END__
ulp(2:+0x1.0000000000000p+1) = 4.44089209850063e-016:+0x1.000000000000
+0p-51
ulp(1:+0x1.0000000000000p+0) = 2.22044604925031e-016:+0x1.000000000000
+0p-52
ulp(0.5:+0x1.0000000000000p-1) = 1.11022302462516e-016:+0x1.0000000000
+000p-53
ulp(0.16:+0x1.47ae147ae147bp-3) = 2.77555756156289e-017:+0x1.000000000
+0000p-55
ulp(1.79769313486232e+308:+0x1.fffffffffffffp+1023) = 1.99584030953472
+e+292:+0x1.0000000000000p+971
ulp(2.2250738585072e-308:+0x1.0000000000000p-1022) = 4.94065645841247e
+-324:+0x0.0000000000001p-1022
ulp(1.1125369292536e-308:+0x0.8000000000000p-1022) = 4.94065645841247e
+-324:+0x0.0000000000001p-1022
ulp(4.94065645841247e-324:+0x0.0000000000001p-1022) = 4.94065645841247
+e-324:+0x0.0000000000001p-1022
ulp(0:+0.0) = 4.94065645841247e-324:+0x0.0000000000001p-1022
ulp(0:-0.0) = 4.94065645841247e-324:+0x0.0000000000001p-1022
ulp(Inf:+inf) = Inf:+inf
ulp(-Inf:-inf) = -Inf:-inf
ulp(NaN:nan) = NaN:nan

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In reply to Re^3: Determining the minimum representable increment/decrement possible? by pryrt
in thread Determining the minimum representable increment/decrement possible? by BrowserUk

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