HueSaturationValue.osl

shader HueSaturationValue(
    float Hue = 0.5,
    float Saturation = 1.0,
    float Value = 1.0,
    float Factor = 1.0
        [[ float min = 0.0,
        float max = 1.0 ]],
    color ColorIn = 0.0
        [[ string label = "Color" ]],
    output color ColorOut = 0.0
        [[ string label = "Color" ]]
) {
    // Ripped from Blender's source code
    color Color = transformc("hsv", ColorIn);
    Color[0] = fmod(Color[0] + Hue + 0.5, 1.0);
    Color[1] = clamp(Color[1] * Saturation, 0.0, 1.0);
    Color[2] *= Value;

    Color = transformc("hsv", "rgb", Color);
    Color = max(Color, 0.0);
    ColorOut = mix(ColorIn, Color, Factor);
}