diff --git a/ieeefloat/ulp b/ieeefloat/ulp
new file mode 100755
index 0000000..4b2660d
--- /dev/null
+++ b/ieeefloat/ulp
@@ -0,0 +1,26 @@
+#!/usr/bin/perl
+
+use warnings;
+use strict;
+
+my $x = $ARGV[0] + 0;
+
+my $d = 1;
+while ($x + $d == $x) {
+    $d *= 2;
+}
+while ($x + $d/2 != $x) {
+    $d /= 2;
+}
+
+printf "ulp+ = %.17e %.17e %.17e\n", $d, $x, $x + $d;
+
+$d = 1;
+while ($x - $d == $x) {
+    $d *= 2;
+}
+while ($x - $d/2 != $x) {
+    $d /= 2;
+}
+
+printf "ulp- = %.17e %.17e %.17e\n", $d, $x, $x - $d;