adding text folder to test ptx generator

ptxtest/test.ispc

@@ -0,0 +1,10 @@
+export void saxpy(const uniform float a, const uniform float x_[], const uniform float y_[], uniform float z_[], const uniform int n)
+{
+  foreach (i = 0 ... n)
+  {
+     const float x = x_[i];
+     const float y = y_[i];
+     const float z = y + a*x;
+     z_[i] = rsqrt(z);
+  }
+}