Roman Numerals

local numerals = {
    I = 1,
    V = 5,
    X = 10,
    L = 50,
    C = 100,
    D = 500,
    M = 1000,
}

local reverseNumerals = {}
for k, v in pairs( numerals ) do
    reverseNumerals[ v ] = k
end

function fromRoman( s )
    local num = 0
    local last = 0
    for value in s:upper():gmatch( "." ) do
        if last < numerals[ value ] then
            num = num - last * 2
        end
        num = num + numerals[ value ]
        last = numerals[ value ]
    end
    return num
end

function toRoman( num )
    local roman = ""
    num = tostring( math.floor( num ) )
    local place = 10 ^ (#num - 1)
    for d in num:gmatch( "." ) do
        local d = tonumber( d )
        if d == 9 and reverseNumerals[ place * 10 ] then
            roman = roman .. reverseNumerals[ place ] .. reverseNumerals[ place * 10 ]
            d = 0
        elseif d > 5 and reverseNumerals[ place * 5 ] then
            roman = roman .. reverseNumerals[ place * 5 ]
            d = d - 5
        elseif d == 4 and reverseNumerals[ place * 5 ] then
            roman = roman .. reverseNumerals[ place ] .. reverseNumerals[ place * 5 ]
            d = 0
        elseif d == 5 and reverseNumerals[ place * 5 ] then
            roman = roman .. reverseNumerals[ place * 5 ]
            d = 0
        end
        roman = roman .. reverseNumerals[ place ]:rep( d )
        place = place / 10
    end
    return roman