+# Various hash size-related values.
+my $sha1_len = 40;
+my $sha256_extra_len = 24;
+my $sha256_len = $sha1_len + $sha256_extra_len;
+
+# A regex matching $len hex characters. $len may be a range (e.g. 7,64).
+sub oid_nlen_regex {
+ my $len = shift;
+ my $hchr = qr/[0-9a-fA-F]/;
+ return qr/(?:(?:$hchr){$len})/;
+}
+
+# A regex matching two sets of $nlen hex characters, prefixed by the literal
+# string $prefix and with the literal string $infix between them.
+sub oid_nlen_prefix_infix_regex {
+ my $nlen = shift;
+ my $prefix = shift;
+ my $infix = shift;
+
+ my $rx = oid_nlen_regex($nlen);
+
+ return qr/^\Q$prefix\E$rx\Q$infix\E$rx$/;
+}
+
+# A regex matching a valid object ID.
+our $oid_regex;
+{
+ my $x = oid_nlen_regex($sha1_len);
+ my $y = oid_nlen_regex($sha256_extra_len);
+ $oid_regex = qr/(?:$x(?:$y)?)/;
+}
+