Test, documentation and vim support for double precision constants

tests/double-consts.ispc

@@ -0,0 +1,23 @@
+
+export uniform int width() { return programCount; }
+
+export void f_f(uniform float RET[], uniform float aFOO[]) {
+    double a = aFOO[programIndex];
+    // Test parsing of double constants.
+    double d1 = 1.0d40;
+    double d2 = 1.d40;
+    double d3 = 1d40;
+    double d4 = 10000000000000000000000000000000000000000.d;
+    double d5 = 10000000000000000000000000000000000000000.0d;
+
+    // All the constants should be equal and if it's evaluated as "float",
+    // then sqrt will evaluate to +inf.
+    if (d1 == d2 && d1 == d3 && d1 == d4 && d1 == d5 &&
+        ((float)sqrt(d1)) < 2e20) {
+        RET[programIndex] = a;
+    }
+}
+
+export void result(uniform float RET[]) {
+    RET[programIndex] = 1 + programIndex;
+}