Solidity Assembly

In this article, we’ll examine Solidity assembly with examples, including its syntax, data types, and control flow structures.

We’ll also cover some common use cases for assembly, such as gas optimization, low-level memory management, and interfacing with external contracts.

Table Of Content-

Assembly or Assembler

An assembly language is a low-level programming language that can be converted to machine code using an assembler.

Assembler languages are either implemented by physical or virtual machines, and these instructions instruct the CPU to do things like add two numbers.

Solidity Assembly

Solidity offers the option of writing assembly language code within smart contract source code.

By using Solidity assembly, we are able to directly interact with the EVM through its opcodes. Using assembly, you can control some logic that cannot be controlled using only solidity, such as pointing to a specific memory block.

One of its main advantages is that it reduces the cost of gas used for deployment.

There are two ways to implement assembly language in Solidity, Inline Assembly and Standalone Assembly.

Inline Assembly

Adding assembly code to solidity code provides fine-grained control and is particularly useful for enhancing the language by adding new libraries.

A solidity statement can contain inline assembly that EVM can understand.

Additionally, it can be applied when the optimizer is not able to produce reliable code.

Assembly local variables, function calls, switch statements, if statements, loops, etc., make solidity easier.

Syntax

assembly{
// assembly language statements
}

The example below will help you to integrate assembly language with solidity. Here we add two variables using the assembly language:

Example: 

pragma solidity ^0.8.0;contract SolidityTest { function add(uint256 a, uint256 b) public pure returns (uint256) { assembly { // Load the values of a and b into registers mstore(0x0, a) mstore(0x20, b) let result := add(a, b)// Return the result mstore(0x0, result) return(0x0, 0x20) } } }
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The program below shows the method of printing a product of two numbers using the assembly language block code:

Example: 

pragma solidity ^0.8.0;contract SolidityTest {function multiply(uint256 a, uint256 b) public pure returns (uint256) { uint256 mrx_result; assembly { // Multiply a and b mrx_result := mul(a, b) } return mrx_result; } }
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Similarly, it is possible to subtract two variables given by the user using the assembly code as follow:

Example: 

pragma solidity ^0.8.0;contract SolidityTest{ function subtract_Variables(uint mrx,uint ample) public pure returns (uint) {uint mrx_result;assembly { // subtract ample from mrx and store the mrx_result on the stack let subResult := sub(mrx, ample)// copy the result from the stack to the mrx_result variable mrx_result := subResult }return mrx_result; } }
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Standalone Assembly

The standalone assembly language is planned to act as an intermediate language for the Solidity compiler.

It was supported for recent compatibility, but no longer appears in the documentation for Solidity.

In standalone assemblies, the code can be read even if it was generated using a solidity compiler.

A simple control flow is needed for optimization and formal verification.

The following example will show you the working of the Standalone Assembly with the solidity contract:

Example: 

pragma solidity ^0.8.0;contract SolidityTest{ function standAlone_Assembly_add(uint mrx) public pure returns (uint ample) { // Here we have assigned the variable ample with a value of 5 ample = 5; // The for loop will be executed until the desired condition is met for (uint n = 0; n < mrx; n++) ample += mrx; } }
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Solidity Assembly Benefits

The following are some benefits of using assembly in Solidity code:

  • Solidity code execution can be controlled precisely through the Assembly language. It is possible to optimize gas costs and make your contracts more efficient by writing low-level code in assembly.
  • Assembly code is faster than Solidity code since it directly accesses the EVM’s native instructions. In contrast, Solidity requires an intermediate compilation process that can be time-consuming.
  • Assembly code offers direct access to the Ethereum Virtual Machine (EVM). In comparison to Solidity’s higher level abstractions, this provides more flexibility and control over the contract’s behavior.
  • Assembly code is generally shorter than equivalent Solidity code. As a result, the contract size can be reduced, thereby reducing gas costs and improving contract deployment.
  • Sometimes debugging Solidity code is difficult, especially when dealing with low-level details like gas costs. The assembly language allows you to debug at a lower level, making it easier for you to isolate and fix code problems.

Conclusion

Solidity assembly language offers you a unique set of benefits for optimizing their smart contracts. Assembly code provides direct access to EVM opcodes for fine-tuning contract execution and improving gas efficiency.

In addition, assembly language can be invaluable for you in optimizing contracts due to its reduced code size and low-level debugging capabilities.

It is important, however, to understand the EVM well before using assembly code.

Solidity assembly language should be chosen based on a careful evaluation of its efficiency, complexity, and maintainability.

It can be highly rewarding for developers who commit the time and effort to master assembly language in terms of contract performance and cost savings.

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