Index: complex.c
===================================================================
--- complex.c	(リビジョン 50638)
+++ complex.c	(作業コピー)
@@ -967,7 +967,7 @@ nucomp_expt(VALUE self, VALUE other)
 	return f_expt(f_reciprocal(self), f_negate(other));
     }
     if (k_numeric_p(other) && f_real_p(other)) {
-	VALUE r, theta;
+	VALUE r, theta, theta2;
 
 	if (k_bignum_p(other))
 	    rb_warn("in a**b, b may be too big");
@@ -974,10 +974,73 @@ nucomp_expt(VALUE self, VALUE other)
 
 	r = f_abs(self);
 	theta = f_arg(self);
+	if (RB_TYPE_P(other, T_BIGNUM) && RBIGNUM_POSITIVE_P(other) &&
+	    k_float_p(theta) && !f_zero_p(theta)) {
+	    double th = RFLOAT_VALUE(theta);
+	    double epsilon;
+	    while (fabs(th) >= M_PI * 2) {
+		if (th < 0) {
+		    th += M_PI * 2;
+		}
+		else {
+		    th -= M_PI * 2;
+		}
+	    }
+	    if (th < 0) {
+		th = th += M_PI * 2;
+	    }
 
-	return f_complex_polar(CLASS_OF(self), f_expt(r, other),
-			       f_mul(theta, other));
+	    epsilon = th * DBL_EPSILON;
+	    if (fabs(th - M_PI_2) <= epsilon) {
+		switch (FIX2INT(rb_big_modulo(other, INT2FIX(4)))) {
+		  case 0:
+		    theta2 = DBL2NUM(0.0);
+		    break;
+		  case 1:
+		    theta2 = DBL2NUM(th);
+		    break;
+		  case 2:
+		    theta2 = DBL2NUM(M_PI);
+		    break;
+		  case 3:
+		    theta2 = DBL2NUM(M_PI+th);
+		    break;
     }
+	    }
+	    else if (fabs(th - M_PI) <= epsilon) {
+		if (f_zero_p(rb_big_modulo(other, INT2FIX(2)))) {
+		    theta2 = DBL2NUM(th);
+		}
+		else {
+		    theta2 = DBL2NUM(0.0);
+		}
+	    }
+	    else if (fabs(th - (M_PI+M_PI_2)) <= epsilon) {
+		switch (FIX2INT(rb_big_modulo(other, INT2FIX(4)))) {
+		  case 0:
+		    theta2 = DBL2NUM(0.0);
+		    break;
+		  case 1:
+		    theta2 = DBL2NUM(M_PI+th);
+		    break;
+		  case 2:
+		    theta2 = DBL2NUM(M_PI);
+		    break;
+		  case 3:
+		    theta2 = DBL2NUM(th);
+		    break;
+		}
+	    }
+	    else {
+		theta2 = f_mul(DBL2NUM(th), other);
+	    }
+	}
+	else {
+	    theta2 = f_mul(theta, other);
+	}
+
+	return f_complex_polar(CLASS_OF(self), f_expt(r, other), theta2);
+    }
     return rb_num_coerce_bin(self, other, id_expt);
 }