How much gas does looking up block.timestamp consume?

Question

Trying to get some insight as to whether or not it's more optimal to call block.timestamp repeatedly for comparisons or to set a (memory) variable to hold the value and use it instead.

I've looked at the gas cost table here:

http://ethdocs.org/en/latest/contracts-and-transactions/account-types-gas-and-transactions.html

but am not certain about where block.timestamp fits in.

Answer 1

The TIMESTAMP op code costs 2 gas, according to the yellow paper (https://ethereum.github.io/yellowpaper/paper.pdf), Appendix G and Appendix H.