bigdecimal.c: Fix special cases of BigDecimal#**

[Bug #18677]

Author: mrkn

ext/bigdecimal/bigdecimal.c

@@ -2769,7 +2769,14 @@ bigdecimal_power_by_bigdecimal(Real const* x, Real const* exp, ssize_t const n)
     VALUE log_x, multiplied, y;
     volatile VALUE obj = exp->obj;
 
-    if (VpIsZero(exp)) {
+    if (VpIsNaN(exp)) {
+        Real *nan = VpCreateRbObject(n, "0", true);
+	RB_GC_GUARD(nan->obj);
+	VpSetNaN(nan);
+        return VpCheckGetValue(nan);
+    }
+
+    if (VpIsZero(exp) || VpIsPosOne(x)) {
         return VpCheckGetValue(VpCreateRbObject(n, "1", true));
     }
 
@@ -2858,15 +2865,16 @@ BigDecimal_power(int argc, VALUE*argv, VALUE self)
 
       case T_DATA:
 	if (is_kind_of_BigDecimal(vexp)) {
-	    VALUE zero = INT2FIX(0);
-	    VALUE rounded = BigDecimal_round(1, &zero, vexp);
-	    if (RTEST(BigDecimal_eq(vexp, rounded))) {
-		vexp = BigDecimal_to_i(vexp);
-		goto retry;
-	    }
-            if (NIL_P(prec)) {
-                GUARD_OBJ(y, GetVpValue(vexp, 1));
-                n += y->Prec*VpBaseFig();
+            if (BigDecimal_IsFinite(vexp)) {
+                VALUE rounded = BigDecimal_round(0, NULL, vexp);
+                if (RTEST(BigDecimal_eq(vexp, rounded))) {
+                    vexp = BigDecimal_to_i(vexp);
+                    goto retry;
+                }
+                if (NIL_P(prec)) {
+                    GUARD_OBJ(y, GetVpValue(vexp, 1));
+                    n += y->Prec*VpBaseFig();
+                }
             }
 	    exp = DATA_PTR(vexp);
 	    break;

ext/bigdecimal/bigdecimal.h

@@ -283,6 +283,7 @@ VP_EXPORT Real *VpOne(void);
 #define VpSetInf(a,s)   (void)(((s)>0)?VpSetPosInf(a):VpSetNegInf(a))
 #define VpHasVal(a)     (a->frac[0])
 #define VpIsOne(a)      ((a->Prec==1)&&(a->frac[0]==1)&&(a->exponent==1))
+#define VpIsPosOne(a)   (((a)->sign>0)&&VpIsOne(a))
 #define VpExponent(a)   (a->exponent)
 #ifdef BIGDECIMAL_DEBUG
 int VpVarCheck(Real * v);

test/bigdecimal/test_bigdecimal.rb

@@ -1492,9 +1492,35 @@ def test_power_with_Bignum
     end
   end
 
-  def test_power_with_BigDecimal
-    assert_nothing_raised do
-      assert_in_delta(3 ** 3, BigDecimal(3) ** BigDecimal(3))
+  data(
+    "BigDecimal(3) ** BigDecimal(3) -> BigDecimal(3**3)" => [BigDecimal(3), BigDecimal(3), BigDecimal(3**3)],
+    "BigDecimal(10) ** Inf -> Inf" => [BigDecimal(10), BigDecimal::INFINITY, :pos_inf],
+    "BigDecimal(10) ** NaN -> NaN" => [BigDecimal(10), BigDecimal::NAN, :nan],
+    "Inf ** BigDecimal(0) -> BigDecimal(1)" => [BigDecimal::INFINITY, BigDecimal(0), BigDecimal(1)],
+    "-Inf ** BigDecimal(0) -> BigDecimal(-1)" => [-BigDecimal::INFINITY, BigDecimal(0), BigDecimal(1)],
+    "BigDecimal(1) ** Inf -> 1" => [BigDecimal(1), BigDecimal::INFINITY, BigDecimal(1)],
+    "BigDecimal(1) ** -Inf -> 1" => [BigDecimal(1), -BigDecimal::INFINITY, BigDecimal(1)],
+    "BigDecimal(0) ** Inf -> 0" => [BigDecimal(0), BigDecimal::INFINITY, BigDecimal(0)],
+    "BigDecimal(0) ** -Inf -> Inf" => [BigDecimal(0), -BigDecimal::INFINITY, :pos_inf],
+    "BigDecimal(-1) ** Inf -> Math::DomainError" => [BigDecimal(-1), BigDecimal::INFINITY, :math_domain_error],
+    "BigDecimal(-1) ** -Inf -> Math::DomainError" => [BigDecimal(-1), -BigDecimal::INFINITY, :math_domain_error]
+  )
+  def test_power_with_BigDecimal(data)
+    BigDecimal.save_exception_mode do
+      BigDecimal.mode(BigDecimal::EXCEPTION_ALL, false)
+      x, y, res = *data
+      case res
+      when :pos_inf
+        assert_nothing_raised { assert_positive_infinite(x ** y) }
+      when :neg_inf
+        assert_nothing_raised { assert_negative_infinite(x ** y) }
+      when :nan
+        assert_nothing_raised { assert_nan(x ** y) }
+      when :math_domain_error
+        assert_raise(Math::DomainError) { x ** y }
+      else
+        assert_nothing_raised { assert_in_delta(res, x ** y) }
+      end
     end
   end