Re: Serialization of math.huge

[Coda Highland <chighland@...>]

On Wed, May 30, 2012 at 3:34 AM, Alexander Gladysh <agladysh@gmail.com> wrote:
> On Tue, May 29, 2012 at 9:03 PM, Paul K <paulclinger@yahoo.com> wrote:
>> I've been working on a simple serialization module (yes, I carefully
>> reviewed the implementations listed here
>> http://lua-users.org/wiki/TableSerialization) and came across an issue
>> with math.huge. tostring(math.huge) returns "1.#INF", but this value
>> isn't interpreted as a valid number (when I'm loading the generated
>> string with loadstring). It seems like these values (+/-math.huge)
>> need to be treated as special cases, but I don't see this logic in any
>> of the modules I reviewed (including those that aim to provide a
>> complete serialization solution).
>>
>> A simple test using serialize.lua from metalua:
>>
>> require "serialize"
>> local s = serialize {[math.huge] = -math.huge}
>> local _, err = loadstring(s)
>> print(s, err)
>>
>> This outputs:
>>
>> return { [1.#INF] = -1.#INF }   [string "return { [1.#INF] = -1.#INF
>> }"]:1: ']' expected near '#'
>>
>> Does this indeed need to be handled as a special case, or am I missing
>> some simple solution?
>
> This is handled in latest lua-nucleo[1] tstr()[2], tserialize()[3] and
> tpretty()[4].
>
> The code to handle the case[5]:
>
> -- convert numbers into loadable string, including inf, -inf and nan
> local serialize_number
> do
>  local t =
>  {
>    [tostring(1/0)] = "1/0";
>    [tostring(-1/0)] = "-1/0";
>    [tostring(0/0)] = "0/0";
>  }
>  serialize_number = function(number)
>    -- no argument checking - called very often
>    local text = ("%.17g"):format(number)
>    -- on the same platform tostring() and string.format()
>    -- return the same results for 1/0, -1/0, 0/0
>    -- so we don't need separate substitution table
>    return t[text] or text
>  end
> end
>
> HTH,
> Alexander.
>
> [1] https://github.com/lua-nucleo/lua-nucleo/
> [2] https://github.com/lua-nucleo/lua-nucleo/blob/master/lua-nucleo/tstr.lua
> [3] https://github.com/lua-nucleo/lua-nucleo/blob/master/lua-nucleo/tserialize.lua
> [4] https://github.com/lua-nucleo/lua-nucleo/blob/master/lua-nucleo/tpretty.lua
> [5] https://github.com/lua-nucleo/lua-nucleo/blob/master/lua-nucleo/string.lua#L321-344
>

Hey, the substitution table keyed by tostring() is a clever idea. I
wouldn't have thought of that! Great job. :)

/s/ Adam