I'm new to Solidity and I'm having some troubles with type issues. I'm trying to execute the following functions:

function sigmoidSingle(int128 x) public pure returns(int128)
    //The sigmoid function is f(x) = 1 / (1 + e^(-x))
    x =  ONE + ABDKMath64x64.exp(-x);
    int128 y = ABDKMath64x64.div(ONE,x);
    return y;

//Sigmoid activation function to process a np array
function sigmoid(int128[] memory x) public pure returns(int128[] memory)
    uint xSize = x.length;
    int128[] memory y_Preds = new int128[](xSize);
    for(uint8 i = 0; i < xSize; i++ )
         y_Preds[i] =  sigmoidSingle(x[i]);
    return y_Preds;

where the input array x of the sigmoid function is an array of 64.64 fixed point format numbers. I am converting the numbers with Python taking advantage of the following function:

def toFixedPoint64(x):
    x = x * (2**64)
    y = round(x + 0.5)
    return y

Now, assume that i want to convert the following array of floating point numbers:


The resulting array would be:

[9592306918328967168, 9038904596117680128, -3689348814741910528, 10514644122014443520]

When i give in input this array to sigmoid function, i'm getting the following error:

Error encoding arguments: Error: invalid number value (arg="", coderType="int128", value=9592306918328967000, version=4.0.44)

I don't get why I am having this issue, indeed with an int128 i should be able to represent higher values of this one. Also i don't get why the number is cut to 9592306918328967000. Consider that if I give in input the number 9592306918328967168 to the sigmoidSingle function i don't get any problem, on the contrary it returns the correct result. Now, I suspect that the problem may arise because of the array, but since I'm not a Solidity expert I don't know what to think. Is there anyone who can help me understand the situation?

UPDATE: It is a problem of the VM simulator. Giving the number surrounded by quotation marks should work. Ex: "9592306918328967168" is the correct way to give in input this int128 to Remix GUI.

2 Answers 2


On Python 2, the round() function returns a floating point number (see here).

Switch to Python 3, or use int(round(x + 0.5)) instead.

  • I'm already using python3 and getting properly an integer. The problem is that the sigmoid function doesn't accept the resulting numbers, but i don't understand why, since the numbers should be representable as int128
    – jack_5
    Apr 12, 2020 at 20:29

Just put all the number into double quotes:

[ "9592306918328967168",
  "10514644122014443520" ]

as your numbers are too big to be represented as JSON numbers.

With these quoted values, the output of sigmoid function is:

11568834341578123390, // 0.627147766313195582813
11438944655894070866, // 0.620106432343090129282
8304097042261566175,  // 0.450166002687522088675
11783100815680795823  // 0.638763175148841909118

Also, there is a security issue with your code as -x is unsafe and may cause overflow. You better use ABDKMath64x64.neg(x) instead.

BTW, you may use ABDK Toolkit to convert numbers to/from 64.64 format.

P.S. I'm the author of this ABDKMath64x64 library.

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