Provide MAXGAMMA, MAXLOG, and MINLOG for 64-bit reals.

Also, fix a call to pow() that would overflow for 64-bit reals.

std/internal/math/gammafunction.d

@@ -111,7 +111,14 @@ real gammaStirling(real x)
     }
     else {
         w = 1.0L + w * poly( w, SmallStirlingCoeffs);
-        y = pow( x, x - 0.5L ) / y;
+        if ( (real.mant_dig == 53) && (x > 143.0L) ) {
+            // Avoid overflow in pow() for 64-bit reals
+            real v = pow( x, 0.5L * x - 0.25L );
+            y = v * (v / y);
+        }
+        else {
+            y = pow( x, x - 0.5L ) / y;
+        }    
     }
     y = SQRT2PI * y * w;
     return  y;
@@ -231,7 +238,12 @@ real igammaTemmeLarge(real a, real x)
 
 public:
 /// The maximum value of x for which gamma(x) < real.infinity.
-enum real MAXGAMMA = 1755.5483429L;
+static if (real.mant_dig == 64)  // 80-bit reals
+    enum real MAXGAMMA = 1755.5483429L;
+else static if (real.mant_dig == 53) // 64-bit reals
+    enum real MAXGAMMA = 171.6243769L;
+else
+    static assert(0, "missing MAXGAMMA for other real types");
 
 
 /*****************************************************
@@ -528,8 +540,17 @@ unittest {
 
 
 private {
-enum real MAXLOG = 0x1.62e42fefa39ef358p+13L;  // log(real.max)
-enum real MINLOG = -0x1.6436716d5406e6d8p+13L; // log(real.min*real.epsilon) = log(smallest denormal)
+static if (real.mant_dig == 64) { // 80-bit reals
+    enum real MAXLOG = 0x1.62e42fefa39ef358p+13L;  // log(real.max)
+    enum real MINLOG = -0x1.6436716d5406e6d8p+13L; // log(real.min_normal*real.epsilon) = log(smallest denormal)
+}
+else static if (real.mant_dig == 53) { // 64-bit reals
+    enum real MAXLOG = 0x1.62e430p+9L;  // log(real.max)
+    enum real MINLOG = -0x1.743854p+9L; // log(real.min_normal*real.epsilon) = log(smallest denormal)
+}
+else
+    static assert(0, "missing MAXLOG, MINLOG, BETA_BIG, and BETA_BIGINV for other real types");
+
 enum real BETA_BIG = 9.223372036854775808e18L;
 enum real BETA_BIGINV = 1.084202172485504434007e-19L;
 }