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I have followed following answer for: Having trouble storing multiple values in a uint256.

For example, I want to pass four uint64 variables merged together as a single argument into smart contract and extract those values.

#python-script:

variable1 = 11;
variable2 = 12;
variable3 = 13;
variable4 = 14;

bits1='{0:064b}'.format(v1)
bits2='{0:064b}'.format(v2)
bits3='{0:064b}'.format(v3)
bits4='{0:064b}'.format(v4)    
mergedVariable = int(bits1 + bits2 + bits3 + bits4, 2)
storagetest8.setCharacter(mergedVariable)
print(storagetest8.getVariables())

contract storagetest8 {

    uint256 variable;

    function setCharacter(uint variable_) 
        external 
    {
        variable = variable_;        
    }


    function getVariables() 
        external view
    returns(uint64 variable1, uint64 variable2, uint64 variable3, uint64 variable4) {
        variable1 = uint64(variable);
        variable = uint64(variable>>64); 
        variable2 = uint64(variable);
        variable = uint64(variable>>64);
        variable3 = uint64(variable);
        variable4 = uint64(variable>>64) // simplified 
    }
}

[Q] Is the approach I implemented in the smart contract correct?

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1 Answer 1

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3

Your smart contract code is okay, but this is probably simpler:

pragma solidity 0.5.7;

contract Uncombine {
    function getVariables(uint256 combined) external pure returns (uint64 variable1, uint64 variable2, uint64 variable3, uint64 variable4) {
        variable1 = uint64(combined);
        variable2 = uint64(combined >> 64);
        variable3 = uint64(combined >> 128);
        variable4 = uint64(combined >> 192);
    }
}

Not sure what language your combining code is in, but this will do the trick in a language like Python that supports large enough integers:

combined = 11 + (12 << 64) + (13 << 128) + (14 << 192)
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5
  • In addition, is it possible to store multiple int64 and uint64 variable under uint256 as well? @smarx
    – alper
    Apr 23, 2019 at 17:49
  • Yes, but the combining will be less straightforward. Since you're using Python, you might want to look at struct.pack.
    – user19510
    Apr 23, 2019 at 17:55
  • Yes, I am using Python as well. Let me investigate if variable1 is -1 as int64 and combine it with other variables reminding as uint64, if possible.
    – alper
    Apr 23, 2019 at 17:57
  • How could I update a single variable; is it possible? For example, I want to update only variable2 with 21? @smarx
    – alper
    Apr 24, 2019 at 16:12
  • 1
    Depends on how you're constructing the combined value. (If you're using addition like in my answer, you could just subtract the old value and add the new one.)
    – user19510
    Apr 24, 2019 at 17:11

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