corrected and improved

#! perl -slw
use strict;

my $bigstring="MNRIYSLRYSAVARGFIAVSEFARKCVHKSVRRLCFPVLLLIPVLFSAGSLAGTV
+NNELGYQLFRDFAENKGMFRPGATNIAIYNKQGEFVGTLDKAAMPDFSAVDSEIGVATLINPQYIASVK
+HNGGYTNVSFGDGENRYNIVDRNNAPSLDFHAPRLDKLVTEVAPTAVTAQGAVAGAYLDKERYPVFYRL
+GSGTQYIKDSNGQLTKMGGAYSWLTGGTVGSLSSYQNGEMISTSSGLVFDYKLNGAMPIYGEAGDSGSP
+LFAFDTVQNKWVLVGVLTAGNGAGGRGNNWAVIPLDFIGQKFNEDNDAPVTFRTSEGGALEWSFNSSTG
+AGALTQGTTTYAMHGQQGNDLNAGKNLIFQGQNGQINLKDSVSQGAGSLTFRDNYTVTTSNGSTWTGAG
+IVVDNGVSVNWQVNGVKGDNLHKIGEGTLTVQGTGINEGGLKVGDGKVVLNQQADNKGQVQAFSSVNIA
+SGRPTVVLTDERQVNPDTVSWGYRGGTLDVNGNSLTFHQLKAADYGAVLANNVDKRATITLDYALRADK
+VALNGWSESGKGTAGNLYKYNNPYTNTTDYFILKQSTYGYFPTDQSSNATWEFVGHSQGDAQKLVADRF
+NTAGYLFHGQLKGNLNVDNRLPEGVTGALVMDGAADISGTFTQENGRLTLQGHPVIHAYNTQSVADKLA
+ASGDHSVLTQPTSFSQEDWENRSFTFDRLSLKNTDFGLGRNATLNTTIQADNSSVTLGDSRVFIDKNDG
+QGTAFTLEEGTSVATKDADKSVFNGTVNLDNQSVLNINDIFNGGIQANNSTVNISSDSAVLGNSTLTST
+ALNLNKGANALASQSFVSDGPVNISDATLSLNSRPDEVSHTLLPVYDYAGSWNLKGDDARLNVGPYSML
+SGNINVQDKGTVTLGGEGELSPDLTLQNQMLYSLFNGYRNIWSGSLNAPDATVSMTDTQWSMNGNSTAG
+NMKLNRTIVGFNGGTSPFTTLTTDNLDAVQSAFVMRTDLNKADKLVINKSATGHDNSIWVNFLKKPSNK
+DTLDIPLVSAPEATADNLFRASTRVVGFSDVTPILSVRKEDGKKEWVLDGYQVARNDGQGKAAATFMHI
+SYNNFITEVNNLNKRMGDLRDINGEAGTWVRLLNGSGSADGGFTDHYTLLQMGADRKHELGSMDLFTGV
+MATYTDTDASADLYSGKTKSWGGGFYASGLFRSGAYFDVIAKYIHNENKYDLNFAGAGKQNFRSHSLYA
+GAEVGYRYHLTDTTFVEPQAELVWGRLQGQTFNWNDSGMDVSMRRNSVNPLVGRTGVVSGKTFSGKDWS
+LTARAGLHYEFDLTDSADVHLKDAAGEHQINGRKDSRMLYGVGLNARFGDNTRLGLEVERSAFGKYNTD
+DAINANIRYSF";
my $smallstring="GTMARNDGQGKAAATFMHISYNNFITEVDNLNKRMGDLRDINGEAGTWVRLLN
+GSGSADGGFTDHYTLLQMGADRKHELGSMDLFTGVMATYTDTDASADLYSGKTKSWGGGFYASGLFRSG
+AYFDVIAKYIHNENKYDLNFAGAGKQNFRSHSLYAGAEVGYRYHLTDTTFVEPQAELVWGRLQGQTFNW
+NDSGMDVSMRRNSVNPLVGRTGVVSGKTFSGKDWSLTARAGLHYEFDLTDSADVHLKDAAGEHQINGRK
+DSRMLYGVGLNARFGDNTRLGLEVERSAFGKYNTDDAINANIRYSFLE";
my $lenBig = length $bigstring;
my $lenSmall = length $smallstring;
my $threshold = 0.9;

for my $o ( 0 .. $lenBig - $threshold*$lenSmall ) {
    my $masked = substr( $bigstring, $o, $lenSmall ) ^ $smallstring;
    my $matched = $masked =~ tr[\0][];
    if( ( $matched / $lenSmall ) > $threshold ) {
        $masked =~ tr[\1-\255][ ];
        $masked =~ tr[\0][*];
        printf "%.2f%% match at offset %u\n", $matched / $lenSmall * 1
+00, $o;
        print substr $bigstring, $o, $lenSmall;
        print $smallstring;
        print $masked;
    }
}
[download]

98.05% match at offset 1071
YQVARNDGQGKAAATFMHISYNNFITEVNNLNKRMGDLRDINGEAGTWVRLLNGSGSADGGFTDHYTLLQ
+MGADRKHELGSMDLFTGVMATYTDTDASADLYSGKTKSWGGGFYASGLFRSGAYFDVIAKYIHNENKYD
+LNFAGAGKQNFRSHSLYAGAEVGYRYHLTDTTFVEPQAELVWGRLQGQTFNWNDSGMDVSMRRNSVNPL
+VGRTGVVSGKTFSGKDWSLTARAGLHYEFDLTDSADVHLKDAAGEHQINGRKDSRMLYGVGLNARFGDN
+TRLGLEVERSAFGKYNTDDAINANIRYSF
GTMARNDGQGKAAATFMHISYNNFITEVDNLNKRMGDLRDINGEAGTWVRLLNGSGSADGGFTDHYTLLQ
+MGADRKHELGSMDLFTGVMATYTDTDASADLYSGKTKSWGGGFYASGLFRSGAYFDVIAKYIHNENKYD
+LNFAGAGKQNFRSHSLYAGAEVGYRYHLTDTTFVEPQAELVWGRLQGQTFNWNDSGMDVSMRRNSVNPL
+VGRTGVVSGKTFSGKDWSLTARAGLHYEFDLTDSADVHLKDAAGEHQINGRKDSRMLYGVGLNARFGDN
+TRLGLEVERSAFGKYNTDDAINANIRYSFLE
   ************************* *****************************************
+*********************************************************************
+*********************************************************************
+*********************************************************************
+*****************************
[download]