Solidity – Available Fixed and Floating Point Math Libraries

floating-pointsolidity

Solidity doesn't have float or double variables. What solutions are there to handle the cases where we really have to represent numbers as percentages or fractions?

Best Answer

Disclaimer: I am the author of PRBMath.

Fixed-Point

PRBMath
- signed and unsigned denary numbers with 18 decimals of precisions
- offers advanced math functions (logs, exp, pow, etc.)
- bakes in overflow-safe multiplication and division
- ultra gas efficient
ABDKMath64x64
- binary numbers with 2^64 precision
- offers advanced math functions (logs, exp, pow, etc.)
- ultra gas efficient (see this praise)
Fixidity
- denary numbers with arbitrary number of decimals
- offers advanced math functions (logs, exp, pow, etc.)
- slower than 64.64, but with a more palatable API
- used by CementDAO, PoolTogether and Celo
Exponential
- denary numbers with 18 decimals of precision
- minimal features, doesn't offer advanced math functions
- developed by Compound.Finance
DecimalMath
- denary numbers with 27 decimals of precision
- minimal features, doesn't offer advanced math functions
- uses ABIEncoderV2 (experimental in Solidity 0.7 and below)
DSMath
- denary numbers with 18 (WAD) and 27 decimals of precision (RAY)
- minimal features, doesn't offer advanced math functions
- developed by the DappHub team, used by the Maker protocol

Floating-Point

ABDKMathQuad
- developed by the same company as 64.64
Bankex
- IEEE-754 octuple precision floating-point

Addenda

There's an open issue in the solidity repo for adding native support for fixed-point types
Mikhail Vladimirov's Math in Solidity blog series is a fantastic resource to learn about how advanced math functions can be implemented in Solidity v0.6 and lower
There are more math libraries mentioned in this OpenZeppelin forum post

Related Solutions

Solidity Data Types – Understanding Fixed and Ufixed Data Types in Solidity

According to the docs: http://solidity.readthedocs.io/en/latest/types.html#fixed-point-numbers

Fixed point numbers are not fully supported by Solidity yet. They can be declared, but cannot be assigned to or from.

So to answer your question, they exist, but you can't use them yet.

When they become supported, you'll be able to use them to represent a number with a fixed number of decimal places.

A side note, I found this question, because I need to store a dollar value in my contract. It seems as though I will either have to store cents as a uint or just use a string... probably going with cents, so that I can easily perform operations... Not sure if that helps you.

Solidity Guide – Understanding Private Variables in Solidity

According to Solidity Documentation:

Private functions and state variables are only visible for the contract they are defined in and not in derived contracts.

In Sol, the private keyword doesn't really mean it is private to the contract consumers. What it means is for example that: a contract B imports contract A and contract A has a private variable V. From contract B, you cant change variable V.

contract A {

    string private V;

}

contract B is A{
    ...
    can't change A.V
    ...
}

hope it helps

[EDIT] - Typo