Bump reference platform to Ubuntu 18.04 LTS (#3037)

Ubuntu 14.04 reached its end of life on April 30m 2019.
Let's bump the reference to the latest LTS, which is 18.04.

Ubuntu 18.04 has newer Pylint and Cppcheck, the necessary
fixes and suppresses are also included in this PR.

JerryScript-DCO-1.0-Signed-off-by: Csaba Osztrogonác oszi@inf.u-szeged.hu

jerry-libm/acos.c

@@ -88,7 +88,7 @@ acos (double x)
         return pi + 2.0 * pio2_lo;
       }
     }
-    return (x - x) / (x - x); /* acos(|x|>1) is NaN */
+    return NAN; /* acos(|x|>1) is NaN */
   }
   if (ix < 0x3fe00000) /* |x| < 0.5 */
   {

jerry-libm/asin.c

@@ -89,7 +89,7 @@ asin (double x)
     {
       return x * pio2_hi + x * pio2_lo;
     }
-    return (x - x) / (x - x); /* asin(|x|>1) is NaN */
+    return NAN; /* asin(|x|>1) is NaN */
   }
   else if (ix < 0x3fe00000) /* |x| < 0.5 */
   {

jerry-libm/atan2.c

@@ -82,7 +82,7 @@ atan2 (double y, double x)
   {
     return atan (y);
   }
-  m = ((hy >> 31) & 1) | ((hx >> 30) & 2); /* 2 * sign(x) + sign(y) */
+  m = ((hy < 0) ? 1 : 0) + ((hx < 0) ? 2 : 0); /* 2 * sign(x) + sign(y) */
 
   /* when y = 0 */
   if ((iy | ly) == 0)

jerry-libm/exp.c

@@ -197,7 +197,7 @@ exp (double x) /* default IEEE double exp */
   }
   if (k >= -1021)
   {
-    ret.as_int.hi += (k << 20); /* add k to y's exponent */
+    ret.as_int.hi += (((unsigned int) k) << 20); /* add k to y's exponent */
     return ret.dbl;
   }
   else

jerry-libm/fmod.c

@@ -53,7 +53,7 @@ fmod (double x, double y)
   if ((hy | ly) == 0 || (hx >= 0x7ff00000) || /* y = 0, or x not finite */
       ((hy | ((ly | -ly) >> 31)) > 0x7ff00000)) /* or y is NaN */
   {
-    return (x * y) / (x * y);
+    return NAN;
   }
   if (hx <= hy)
   {
@@ -123,7 +123,7 @@ fmod (double x, double y)
     n = -1022 - ix;
     if (n <= 31)
     {
-      hx = (hx << n) | (lx >> (32 - n));
+      hx = (((unsigned int) hx) << n) | (lx >> (32 - n));
       lx <<= n;
     }
     else
@@ -141,7 +141,7 @@ fmod (double x, double y)
     n = -1022 - iy;
     if (n <= 31)
     {
-      hy = (hy << n) | (ly >> (32 - n));
+      hy = (((unsigned int) hy) << n) | (ly >> (32 - n));
       ly <<= n;
     }
     else

jerry-libm/pow.c

@@ -254,12 +254,12 @@ pow (double x, double y)
     }
   }
 
-  n = (hx >> 31) + 1;
+  n = (hx < 0) ? 0 : 1;
 
   /* (x<0)**(non-int) is NaN */
   if ((n | yisint) == 0)
   {
-    return (x - x) / (x - x);
+    return NAN;
   }
 
   s = one; /* s (sign of result -ve**odd) = -1 else = 1 */

jerry-libm/sqrt.c

@@ -125,7 +125,7 @@ sqrt (double x)
     }
     else if (ix0 < 0) /* sqrt(-ve) = sNaN */
     {
-      return (x - x) / (x - x);
+      return NAN;
     }
   }
   /* normalize x */