Saturation arithmetic (sub and add) was added for int32/int64.

tests/paddus_vi64.ispc

@@ -0,0 +1,21 @@
+
+export uniform int width() { return programCount; }
+
+export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
+    varying unsigned int64 a_max = 18446744073709551615, a_min = 0; // max and min unsigned int64
+    if (programIndex % 2 == 0) {
+        RET[programIndex] = saturating_add(a_max, b);
+    }
+    else {
+        RET[programIndex] = saturating_add(a_min, b);
+    } 
+}
+
+export void result(uniform float RET[]) {
+    if (programIndex % 2 == 0) {
+        RET[programIndex] = (varying unsigned int64) 18446744073709551615;
+    }
+    else {
+        RET[programIndex] = (varying unsigned int64) 5;
+    } 
+}