--[[
The function does curve conversion f(inputValue) = outputValue
Example of a curve, having multiple ranges of kx + b, set in a register of a String type with Json 
[{"k":4.167,"b":0,"range":[0,3]},{"k":0,"b":12.5,"range":[3,27]},{"k":-4.167,"b":125,"range":[27,30]}]
--]]
function getCurveValue (curveReg, inputValue)

    local s, e = 1, 2                           -- start & end indexes of the subranges 
    local tab = cjson.decode( R(curveReg) )
    local outputValue, stickOutflag
    
    for _, sub_ in ipairs(tab) do 
        if ( (sub_.range[s] <= inputValue) and (inputValue < sub_.range[e]) ) then 
            return (inputValue * sub_.k + sub_.b), nil                             -- normal sequence 
        end
    end
    -- edge cases 
    if  (inputValue < tab[s].range[s]) then 
        outputValue = tab[s].range[s] * tab[s].k + tab[s].b 
        stickOutflag = 1 
    elseif (inputValue > tab[#tab].range[e]) then 
        outputValue = tab[#tab].range[e] * tab[#tab].k + tab[#tab].b
        stickOutflag = #tab 
    end
    return outputValue, stickOutflag
end