Understanding OP_PUSHDATAs in Ethereum Scripting
When working with the Ethereum scripting language, one of the key features to ensure efficient and compact encoding is the use of
OP_PUSHDATAs. In this article, we will look at how these encoded values are constructed and what they mean.
What is OP PUSHDATA?
The OP_PUSHDATA (Opcodes for Push Data) value is a type of opcode that instructs the Ethereum Virtual Machine (EVM) to push data onto the stack. These values are used in various script functions, including push, call, and delegatedCall.
How is OP PUSHDATA Encoded?
The OP PUSHDATA encoding has a specific structure:
- The first byte specifies whether the value is signed or unsigned.
- The next two bytes contain the data to be pushed onto the stack.
Here is an example:
0x1 0x00 0x01
In this case, “0x1” means that the encoded value is signed (i.e. negative), and “0x00” and “0x01” represent the data to be sent to the stack.
Represents unsigned integers
When using OP_PUSHDATA as unsigned integers, you can treat them as 32-bit unsigned integers. This allows you to store and compare these values efficiently.
For example:
0x12345678
In this case, “0x12345678” is a single unsigned integer.
Represents integers
When using OP_PUSHDATA as integers, you need to consider the possibility of overflow or underflow. To mitigate these risks, EVM uses a technique called
packing, where multiple data values are stored in a single byte or word.
For example:
0x12345678
|--- (signed integer)
In this case, “0x12345678” means both signed and unsigned integer.
Conclusion
OP_PUSHDATA provides a flexible and efficient way to encode data values in Ethereum scripts. By understanding the structure of the encoded values and what they mean, developers can write more efficient and readable code. Whether you are working with signed or unsigned integers, EVM’s packing technique ensures that your code is safe and reliable.