While the OP specified that the second string is always the shortest, I wanted one that worked without that restriction:

#! perl -slw
use strict;
use Benchmark qw[ cmpthese ];
use List::MoreUtils qw[ zip ];

sub zipA {
    my( $str1, $str2 ) = @_;
    $str1 =~ s/.\K/ substr $str2, 0, 1, ''/gesr;
}

sub zipB {
    no warnings qw/ uninitialized /;
    my( $a, $b ) = @_;
    my @a1 = split( '', $a );
    my @a2 = split( '', $b );
    return join'', zip @a1, @a2;
}

sub zipC($$){
   my( $n, $a, $b ) = ( 1, @_ );
   substr( $a, $n, 0, $_), $n += 2 for split '', $b;
   return $a;
};;

sub zipR {
    my ($s1, $s2) = @_;
    my ($ls1, $ls2, $l, $tmp) = (length($s1), length($s2));
    $l = $ls1<$ls2 ? $ls1 : $ls2;
    $tmp = join("", map{substr($s1,$_,1), substr($s2,$_,1)} 0 .. $l-1)
         . substr($l==$ls2 ? $s1 : $s2,$l);
    return $tmp;
}


sub zipD {
    my ($str1, $str2) = @_;
    for (0 .. length $str2) {
        substr $str1, $_ * 2 + 1, 0, substr $str2, $_, 1;
    }
    return $str1;
}

our $A = 'ABCDEFGHIJ';
our $B = 'abcde';

my (%tests,%results);
for my $T (qw(A B C D R)) {
    $tests{$T.'a'} = "my \$z = zip$T( \$A, \$B )";
    $tests{$T.'b'} = "my \$z = zip$T( \$B, \$A )";
    my $a = eval($tests{$T.'a'});
    my $b = eval($tests{$T.'b'});
}

my %R = ( a=>eval $tests{Ba}, b=>eval $tests{Bb} );
print "Expected: a=<$R{a}>, b=<$R{b}>";

for my $test (sort keys %tests) {
    no warnings 'uninitialized';
    my $S = eval $tests{$test};
    my $R = $R{substr($test,1,1)};
    if ($R ne $S) {
        print "test $test failed: <$S>";
        delete $tests{$test};
    }
}

cmpthese -1, \%tests;
__END__
$ perl 1133865.pl
Expected: a=<AaBbCcDdEeFGHIJ>, b=<aAbBcCdDeEFGHIJ>
test Ab failed: <aAbBcCdDeE>
test Cb failed: <>
test Db failed: <>
       Rate   Bb   Ba   Aa   Rb   Ra   Ca   Da
Bb 105326/s   --   0% -62% -69% -69% -81% -86%
Ba 105326/s   0%   -- -62% -69% -69% -81% -86%
Aa 276648/s 163% 163%   -- -18% -19% -50% -62%
Rb 336364/s 219% 219%  22%   --  -1% -39% -54%
Ra 339856/s 223% 223%  23%   1%   -- -39% -54%
Ca 553781/s 426% 426% 100%  65%  63%   -- -25%
Da 735965/s 599% 599% 166% 119% 117%  33%   --

[download]

So I have the fastest one that works without that restriction. (Prediction, someone else will hold that title within 20 minutes......)

...roboticus

When your only tool is a hammer, all problems look like your thumb.

In reply to Re^2: Merge 2 strings like a zip [benchmark] by roboticus
in thread Merge 2 strings like a zip by tel2

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.