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

[download]

In reply to Re^4: Normalizing a range of numbers to a percentage by Lotus1
in thread Normalizing a range of numbers to a percentage by stevieb

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.