# captured UNIX time
C++ 1.0          : 0.450s
C++ fast_io      : 0.291s
Perl MCE 64 thds : 0.252s

##</code><code>##

# HASH
my %rtoa = ( M=>1000, D=>500, C=>100, L=>50, X=>10, V=>5, I=>1 );

# ARRAY, characters M  D  C  L  X  V  I
my @rtoa; @rtoa[qw( 77 68 67 76 88 86 73 )] = qw( 1000 500 100 50 10 5 1 );

Perl MCE 64 thds : 0.252s  @rtoa{ split //, uc($_) };
Perl MCE 64 thds : 0.297s  @rtoa[ map ord, split //, uc($_) ];
Perl MCE 64 thds : 0.192s  @rtoa[ unpack 'c*', uc($_) ];