comment on

I'm quite surprised by your results. It shows the reduce version to be the slowests, and it suggests that using a map with a block is faster than a for statement modifier. The former needs to enter/leave a block for each iteration, and the latter doesn't. A benchmark on my box shows different results:

#!/usr/bin/perl

use strict;
use warnings;

use Benchmark  qw /cmpthese timethese/;
use List::Util qw /reduce/;

our @list = 1 .. 50;

our ($map_b, $map_e, $for_m, $for_b, $red, $bc, $eval);

print "Perl version: $].\n";
system "cat /proc/version";

cmpthese -10  => {
    map_block =>   '$::map_b = 1; map {$::map_b *= $_} @::list',
    map_expr  =>   '$::map_e = 1; map  $::map_e *= $_, @::list',
    for_mod   =>   '$::for_m = 1; $::for_m *= $_ for @::list',
    for_block =>   '$::for_b = 1; foreach (@::list) {$::for_b *= $_}',
    reduce    =>   '$::red   = reduce {$a * $b} @::list',
    bc        => q !local $" = "*";
                    $::bc    = `echo '@::list' | bc`!,
    eval      =>   '$::eval  = eval join "*" => @::list',
};

print "Map block:    $map_b\n";
print "Map expres:   $map_e\n";
print "For modifier: $for_m\n";
print "For block:    $for_b\n";
print "Reduce:       $red\n";
print "bc:           $bc\n";
print "Eval:         $eval\n";
__END__

Perl version: 5.008003.
Linux version 2.4.18-3 (bhcompile@daffy.perf.redhat.com) (gcc version 
+2.96 20000731 (Red Hat Linux 7.3 2.96-110)) #1 Thu Apr 18 07:37:53 ED
+T 2002
             Rate       bc     eval map_block for_block map_expr for_m
+od  reduce
bc         2779/s       --     -55%      -88%      -94%     -95%    -9
+5%    -95%
eval       6199/s     123%       --      -73%      -87%     -88%    -8
+8%    -89%
map_block 22904/s     724%     269%        --      -53%     -55%    -5
+7%    -60%
for_block 49041/s    1664%     691%      114%        --      -3%     -
+9%    -13%
map_expr  50669/s    1723%     717%      121%        3%       --     -
+6%    -11%
for_mod   53638/s    1830%     765%      134%        9%       6%      
+--     -5%
reduce    56651/s    1938%     814%      147%       16%      12%      
+6%      --
Map block:    3.0414093201713378e+64
Map expres:   3.0414093201713378e+64
For modifier: 3.0414093201713378e+64
For block:    3.0414093201713378e+64
Reduce:       3.0414093201713378e+64
bc:           30414093201713378043612608166064768844377641568960512000
+000000000

Eval:         3.0414093201713378e+64
[download]

Abigail

In reply to Re: Product of a list of numbers? by Abigail-II
in thread Product of a list of numbers? by ruffer_rinsin

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