Check numeric shifts for two's complement semantics.

S03-operators/numeric-shift.t

@@ -0,0 +1,31 @@
+use v6;
+use Test;
+
+plan 36;
+
+sub check ($a, $b, $ls, $rs) {
+    is $a * 2**$b, $ls, "expected value for shl $a by $b is sane";
+
+    # assume two's complement semantics for negative $a
+    is floor($a / 2**$b), $rs, "expected value for shr $a by $b is sane";
+
+    is $a +<  $b, $ls, "got expected value for shl $a by $b";
+
+    #?niecza skip 'shift by negative bit count'
+    is $a +< -$b, $rs, "got expected value for shl $a by -$b";
+
+    is $a +>  $b, $rs, "got expected value for shr $a by $b";
+
+    #?niecza skip 'shift by negative bit count'
+    is $a +> -$b, $ls, "got expected value for shr $a by -$b";
+}
+
+check 15, 3, 120, 1;
+check 16, 3, 128, 2;
+check 17, 3, 136, 2;
+
+check -15, 3, -120, -2;
+check -16, 3, -128, -2;
+check -17, 3, -136, -3;
+
+done;