bignum.c (rb_int_powm): Integer#pow(0, 1) should return 0

... instead of 1 because it requires "modulo 1".  [Bug #17257]

bignum.c

@@ -7136,6 +7136,7 @@ rb_int_powm(int const argc, VALUE * const argv, VALUE const num)
             long const half_val = (long)HALF_LONG_MSB;
             long const mm = FIX2LONG(m);
             if (!mm) rb_num_zerodiv();
+            if (mm == 1) return INT2FIX(0);
             if (mm <= half_val) {
                 return int_pow_tmp1(rb_int_modulo(a, m), b, mm, nega_flg);
             }
@@ -7145,6 +7146,7 @@ rb_int_powm(int const argc, VALUE * const argv, VALUE const num)
         }
         else {
             if (rb_bigzero_p(m)) rb_num_zerodiv();
+	    if (bignorm(m) == INT2FIX(1)) return INT2FIX(0);
             return int_pow_tmp3(rb_int_modulo(a, m), b, m, nega_flg);
         }
     }

test/ruby/test_numeric.rb

@@ -435,6 +435,26 @@ class TestNumeric < Test::Unit::TestCase
     assert_equal(12, 12.pow(1, 10000000001), '[Bug #14259]')
     assert_equal(12, 12.pow(1, 10000000002), '[Bug #14259]')
     assert_equal(17298641040, 12.pow(72387894339363242, 243682743764), '[Bug #14259]')
+
+    integers = [-2, -1, 0, 1, 2, 3, 6, 1234567890123456789]
+    integers.each do |i|
+      assert_equal(0, i.pow(0, 1), '[Bug #17257]')
+      assert_equal(1, i.pow(0, 2))
+      assert_equal(1, i.pow(0, 3))
+      assert_equal(1, i.pow(0, 6))
+      assert_equal(1, i.pow(0, 1234567890123456789))
+
+      assert_equal(0,  i.pow(0, -1))
+      assert_equal(-1, i.pow(0, -2))
+      assert_equal(-2, i.pow(0, -3))
+      assert_equal(-5, i.pow(0, -6))
+      assert_equal(-1234567890123456788, i.pow(0, -1234567890123456789))
+    end
+
+    assert_equal(0,  0.pow(2, 1))
+    assert_equal(0,  0.pow(3, 1))
+    assert_equal(0,  2.pow(3, 1))
+    assert_equal(0, -2.pow(3, 1))
   end
 
 end