diff --git a/.gitignore b/.gitignore
index f3056a3..2b49e7e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -19,3 +19,5 @@ cmake_install.cmake
 *.exe
 lib/
 include/
+build/
+bin/
\ No newline at end of file
diff --git a/src/spatial/m_geometry.f90 b/src/spatial/m_geometry.f90
index 41780f8..5e13d9f 100644
--- a/src/spatial/m_geometry.f90
+++ b/src/spatial/m_geometry.f90
@@ -161,6 +161,36 @@ module function orient3D(ax, ay, az, bx, by, bz, cx, cy, cz, dx, dy, dz) result(
       !! [-ve, 0, +ve] for point d [right, on, left] of the plane defined by points a -> b -> c
     end function
   end interface
+  
+  interface
+    module subroutine fastTwoDiff(a, b, x, y)
+      !! Compute the difference two numbers and compute the numerical round-off error.
+      !! This should only be used if you know that the magnitude of a is greater than or equal to b, otherwise, you should use the slower twoDiff routine
+    !====================================================================!
+      real(r64), intent(in) :: a
+        !! First number
+      real(r64), intent(in) :: b
+        !! Second number
+      real(r64), intent(out) :: x
+        !! Result
+      real(r64), intent(out) :: y
+    end subroutine
+  end interface
+
+  interface
+    module subroutine fastTwoSum(a, b, x, y)
+      !! Compute the sum of two numbers and compute the numerical round-off error.
+      !! This should only be used if you know that the magnitude of a is greater than or equal to b, otherwise, you should use the slower twoSum routine
+    !====================================================================!
+      real(r64), intent(in) :: a
+        !! First number
+      real(r64), intent(in) :: b
+        !! Second number
+      real(r64), intent(out) :: x
+        !! Result
+      real(r64), intent(out) :: y
+    end subroutine
+  end interface
 
   interface
     !====================================================================!