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Day 11

I am approaching the end of the challenge, and in my opinion this is the most fun part. I will need to redo most of my main EVM class to allow for the CALL and CREATE operations, but I am looking forward to it.

Today I implemented EXTCODESIZE which was pretty easy, I just had to modify my buildState function to also include the code of any external account provided in the test. Then it was just a matter of returning the size of the code of the account pulled from the stack.

After that, I tried my hand at EXTCODECOPY. This one was definitely one of the longest ones in terms of lines of code, but after having dealt with many Opcodes handling memory slices and manipulating them, I was able to complete it quite quickly.

Here's a rundown of what EXTCODECOPY does: fun-fact, it's the first Opcode I encountered that takes 4 arguments from the stack!

function EXTCODECOPY(ms: MachineState) {
  // We want to copy a portion of code of the account at the `address` on the stack
  // into the memory slice starting at the `offset` and of length `size` bytes

  // the first argument is the address of the account to copy the code from
  const address = ms.stack.pop();
  const addressHex = parsers.BigintIntoHexString(address);
  const extAccount = ms.globalState?.getAccount(addressHex);

  // then we load the other 3 arguments
  const memOffset = Number(ms.stack.pop());
  const codeOffset = Number(ms.stack.pop());
  const size = Number(ms.stack.pop());

  // we get the code portion of the external account (it can be undefined)
  // I parsed this as Uint8Array to stay consistent with the main account code
  const codeBytesPortion = extAccount?.code?.subarray(
    codeOffset,
    codeOffset + size
  );

  // we prepare a buffer of the right size from the Uint8Array slice created above
  // also making sure to account for the undefined case
  const codeBuffer = Buffer.from(codeBytesPortion ?? Buffer.alloc(0));

  // we use our usual trick to copy the buffer into the memory slice
  const code = Buffer.alloc(size);
  codeBuffer.copy(code, 0, 0);

  // and finally we write it into memory
  ms.memory.write(memOffset, code, size);
}

I then also implemented SELFBALANCE which was very simply pushing ms.globalState.getBalance(ms.txData.to) onto the stack.

That's it for today!

Progress so far: 91 passed, 101 total.