Create checksum algorithm according to new spec

lib/Fastadb/Util.pm

@@ -0,0 +1,20 @@
+package Fastadb::Util;
+
+use strict;
+use warnings;
+
+require Exporter;
+our @ISA = qw(Exporter);
+our @EXPORT_OK = qw(reference_retrieval_digest);
+
+use Digest::SHA qw/sha512_hex/;
+
+sub reference_retrieval_digest {
+  my ($sequence, $offset) = @_; # offset expressed in bytes
+  $offset = 24 if ! defined $offset;
+  my $digest = sha512_hex($sequence);
+  my $substring = substr($digest, 0, $offset*2); #going into hex from bytes
+  return $substring;
+}
+
+1;

t/checksum.t

@@ -0,0 +1,31 @@
+use strict;
+use warnings;
+use Test::More;
+
+use Fastadb::Util qw/reference_retrieval_digest/;
+use Fastadb::Fmt::Fasta;
+use File::Basename qw/dirname/;
+use File::Spec;
+
+is(reference_retrieval_digest('ACGT'), '68a178f7c740c5c240aa67ba41843b119d3bf9f8b0f0ac36', 'Check basic round tripping of reference retrieval digest');
+
+my $test_data_dir = File::Spec->catdir(File::Spec->rel2abs(dirname(__FILE__)), 'data');
+
+my $fasta_iter = Fastadb::Fmt::Fasta->new(file => File::Spec->catfile($test_data_dir, 'test.fa'), type => 'dna');
+is(
+  reference_retrieval_digest($fasta_iter->iterate()->{sequence}),
+  'b28e54e972297b88324983e18b20420470acac31baff8520',
+  'Checking basic encoding of known sequence test1'
+);
+is(
+  reference_retrieval_digest($fasta_iter->iterate()->{sequence}),
+  '999687f722592a0959abb475879ccb3b20064d0ad7bbbd85',
+  'Checking basic encoding of known sequence test2'
+);
+is(
+  reference_retrieval_digest($fasta_iter->iterate()->{sequence}),
+  '21b4f4bd9e64ed355c3eb676a28ebedaf6d8f17bdc365995',
+  'Checking basic encoding of known sequence test3'
+);
+
+done_testing();