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Re^4: Normalizing a range of numbers to a percentage

by Lotus1 (Vicar)
on Mar 09, 2019 at 17:08 UTC ( #1231087=note: print w/replies, xml ) Need Help??


in reply to Re^3: Normalizing a range of numbers to a percentage
in thread Normalizing a range of numbers to a percentage

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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