Understanding OP_PUSHDATAs in Ethereum Scripting
When working with the Ethereum scripting language, one of the key features that allows for efficient and compact coding is the use of
OP_PUSHDATA. In this article, we will explore how these encoded values are structured 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 scripting functions, including “push”, “call”, and “delegatedCall”.
How to encode OP PUSHDATA?
The encoding of OP PUSHDATA follows a certain structure:
- The first byte indicates 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” indicates that the encoded value is signed (i.e., a negative number), and “0x00” and “0x01” represent the data to be pushed onto the stack.
Indicates unsigned integers
When you use 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” represents a single unsigned integer value.
Indicates integers
When you use OP_PUSHDATA as integers, you must consider the possibility of overflow and underflow. To mitigate this risk, 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” represents both an unsigned and a signed integer value.
Conclusion
OP_PUSHDATA is a flexible and efficient way to encode data values in Ethereum scripts. By understanding how these encoded values are structured and what they represent, 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 secure and reliable.
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