From 19f80abb3260e689b4f41c54eece8e7ebdd4d4cf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lu=C3=ADs=20Fonseca?= <ei10139@fe.up.pt>
Date: Wed, 7 Sep 2016 21:45:06 +0100
Subject: [PATCH] Fix float math.pow when number was negative and power was odd
 (#1492)

---
 app/libc/c_math.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/app/libc/c_math.c b/app/libc/c_math.c
index d60f9348..b3a87b73 100644
--- a/app/libc/c_math.c
+++ b/app/libc/c_math.c
@@ -59,6 +59,7 @@ double pow(double x, double y)
 {
     double frexp(), g, ldexp(), r, u1, u2, v, w, w1, w2, y1, y2, z;
     int iw1, m, p;
+    bool flipsignal = false;
 
     if (y == 0.0)
         return (1.0);
@@ -67,7 +68,7 @@ double pow(double x, double y)
         if (x == 0.0)
         {
             if (y > 0.0)
-                return (x);
+                return 0.0;
             //cmemsg(FP_POWO, &y);
             //return(HUGE);
         }
@@ -75,6 +76,11 @@ double pow(double x, double y)
         {
             //cmemsg(FP_POWN, &x);
             x = -x;
+
+            if (y != (int) y) { // if y is fractional, then this woud result in a complex number
+                return NAN;
+            }
+            flipsignal = ((int) y) & 1;
         }
     }
     g = frexp(x, &m);
@@ -125,7 +131,8 @@ double pow(double x, double y)
     p = 16 * m - iw1;
     z = ((((((q7 * w2 + q6) * w2 + q5) * w2 + q4) * w2 + q3) * w2 + q2) * w2 + q1) * w2;
     z = a1[p] + a1[p] * z;
-    return (ldexp(z, m));
+    double res = ldexp(z, m);
+    return flipsignal ? -res : res;
 }
 
 #if 0