see Wikipedia and Shaderific

The SmoothstepCHOP has a range input: Fromrange1, and Fromrange2. It also has a range output: Torange1, and Torange2. For an input value x, the SmoothstepCHOP is equivalent to the following GLSL code: return mix(Torange1, Torange2, smoothstep(Fromrange1, Fromrange2, x));

There are alternative modes such as "smootherstep", "smootheststep", and "linear clamp".

Build the dll yourself, or use of the compiled DLL files. CPlusPlusCHOP/build/SmoothstepCHOP.dll has been compiled for TouchDesigner 2018.26750 and CustomOperator/build/SmoothstepCHOP.dll has been compiled for TouchDesigner 2019.17550. This newer version can be used as a Custom Operator

• 2019-08-07 create a Custom Operator version for TD 2019.17550.
• 2019-07-16 working version of smoothstep, smootherstep, smootheststep, and linear clamp.

• Ken Perlin
• Kyle McDonald
• Wolfram Alpha