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

tests/psubus_i32.ispc

@@ -0,0 +1,21 @@
+
+export uniform int width() { return programCount; }
+
+export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
+    uniform unsigned int32 a_max = 4294967295, a_min = 0; // max and min unsigned int32
+    if (programIndex % 2 == 0) {
+        RET[programIndex] = saturating_sub(a_min, b);
+    }
+    else {
+        RET[programIndex] = saturating_sub(a_max, b);
+    } 
+}
+
+export void result(uniform float RET[]) {
+    if (programIndex % 2 == 0) {
+        RET[programIndex] = (uniform unsigned int32) 0;
+    }
+    else {
+        RET[programIndex] = (uniform unsigned int32) 4294967290;
+    } 
+}