$ /usr/local/bin/perl5.10.1  921987.pl
       Rate    b    a    c    d
b 4497569/s   --  -2% -21% -26%
a 4591346/s   2%   -- -19% -25%
c 5681139/s  26%  24%   --  -7%
d 6116693/s  36%  33%   8%   --

$ /usr/local/bin/perl5.10.1 -v

This is perl, v5.10.1 (*) built for x86_64-linux-thread-multi

$ /usr/local/bin/perl5.12.2  921987.pl
       Rate    a    b    c    d
a 4314282/s   --  -8% -30% -36%
b 4677165/s   8%   -- -24% -31%
c 6168093/s  43%  32%   --  -9%
d 6779346/s  57%  45%  10%   --

$ /usr/local/bin/perl5.12.2 -v

This is perl 5, version 12, subversion 2 (v5.12.2) built for x86_64-linux-thread-multi