From f56c72c53dd8d9384475d28e0c1e29448c5db43d Mon Sep 17 00:00:00 2001
From: Sam Hocevar <sam@hocevar.net>
Date: Fri, 23 Dec 2011 02:43:32 +0000
Subject: [PATCH] core: fix the sign of a negative real number raised to an
 even power, and add the corresponding unit test.

---
 src/real.cpp       |  6 ++++++
 test/unit/real.cpp | 11 +++++++++++
 2 files changed, 17 insertions(+)

diff --git a/src/real.cpp b/src/real.cpp
index f62b5ec9..c0a01da7 100644
--- a/src/real.cpp
+++ b/src/real.cpp
@@ -692,8 +692,14 @@ real pow(real const &x, real const &y)
         return exp(y * log(x));
     else /* x < 0 */
     {
+        /* Odd integer exponent */
+        if (y == (round(y >> 1) << 1))
+            return exp(y * log(-x));
+
+        /* Even integer exponent */
         if (y == round(y))
             return -exp(y * log(-x));
+
         /* FIXME: negative nth root */
         return real::R_0;
     }
diff --git a/test/unit/real.cpp b/test/unit/real.cpp
index 70612ef9..b64c3e3b 100644
--- a/test/unit/real.cpp
+++ b/test/unit/real.cpp
@@ -326,6 +326,17 @@ LOLUNIT_FIXTURE(RealTest)
             LOLUNIT_ASSERT_EQUAL(b2, a2);
         }
     }
+
+    LOLUNIT_TEST(Pow)
+    {
+        double a1 = pow(-real::R_2, real::R_2);
+        double b1 = 4.0;
+        LOLUNIT_ASSERT_DOUBLES_EQUAL(a1, b1, 1.0e-13);
+
+        double a2 = pow(-real::R_2, real::R_3);
+        double b2 = -8.0;
+        LOLUNIT_ASSERT_DOUBLES_EQUAL(a2, b2, 1.0e-13);
+    }
 };
 
 } /* namespace lol */