Thanks for the explanation about the float conversions and hash memoization.

The array lookup is quite a bit faster than the string index. I didn't see in the OP that the result had to be integers. The OP showed floats as the output. Edit: The array lookup method will work equally well with either floats or ints since the int() function is not in the part that does the lookup.

#!/usr/bin/env perl
use warnings;
use strict;
use Benchmark 'cmpthese';

my $lookup = join '', map{ chr( $_ / 255 * 100 ) } 0 .. 255;
my @lookup = map{ int( $_ / 255 * 100 ) } 0 .. 255;
my $const = 100 / 255;

cmpthese(-2, {
    lookup => sub {
        my @output = map { ord( substr $lookup, $_, 1 )} 0 .. 255;
    },
    calc   => sub {
        my @output = map {$_ / 255 * 100} 0 .. 255;
    },
    calc2   => sub {
        my @output = map {$_ * $const} 0 .. 255;
    },
    arraylookup   => sub {
        my @output = map { $lookup[ $_ ] } 0 .. 255;;
    },
});

my @output1 = map { ord( substr $lookup, $_, 1 )} 0 .. 5;
my @output2 = map {$_ * $const} 0 .. 5;
print "@output1\n";
print "@output2\n";
__END__

# Results on my machine (v5.22.1 built for MSWin32-x64-multi-thread):
               Rate        calc       calc2      lookup arraylookup
calc        11990/s          --        -25%        -31%        -47%
calc2       15929/s         33%          --         -9%        -30%
lookup      17496/s         46%         10%          --        -23%
arraylookup 22838/s         90%         43%         31%          --
0 0 0 1 1 1
0 0.392156862745098 0.784313725490196 1.17647058823529 1.5686274509803
+9 1.96078431372549
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