EVM Deep Dives: The Path to Shadowy Super Coder 🥷 💻 - Part 2

✅ The Memory is a big volatile array

■ Memory Data Structure

• Store
  • 8-bit
    • MSTORE8 (x, y) - Store a 1 byte (8-bit) value “y” at memory location “x” (the least significant byte of the 32-byte stack value).
  • 256-bit
    • MSTORE (x, y) - Store a 32 byte (256-bit) value “y” starting at memory location “x”
• Load
  • 256-bit
    • MLOAD (x) - Load 32 bytes (256-bit) starting at memory location “x” onto the call stack

You can think of the memory location as simply the array index

This is a good example of how to work memory opcodes ⇒ EVM playgroundW%20at~V%2F%2F%20MQ%20%7B0x2N%20memoryKwg8%201j_J32I11GpPUSHFpMgCn%20Be%209%20i7%20t*%20J)LOAD(js!uu%01!()*79BCFGIJKNQVWXYZ_dgjpquvwz~_)

■ Memory Expansion

If you are writing to an area of memory that hasn't been written to before, there is an additional memory expansion cost for using it for the first time.

Memory expansion costs scale linearly for the first 724 bytes and quadratically after that.

Note that all locations in memory are well-defined initially as zero which is why we see 2200000000000000000000000000000000000000000000000000000000000000 added to our memory.

64 hex = 32 bytes

■ Remember Memory is a Byte Array

Remember memory is a byte array meaning we can start our reads (and our writes) from any memory location

• Example(In this EVM playgroundW%20at~V%2F%2F%20MQ%20%7B0x2N%20memoryKwg8%201j_J32I11GpPUSHFpMgCn%20Be%209%20i7%20t*%20J)LOAD(js!uu%01!()*79BCFGIJKNQVWXYZ_dgjpquvwz~_))

MLOAD(0) ⇒ 1111111111111111111111111111111111111111111111111111111111111111(64 hex) MLOAD(20) ⇒ 2233000000000000000000000000000000000000000000000000000000000000(64hex) MLOAD(21) ⇒ 3300000000000000000000000000000000000000000000000000000000000000(64hex)