GNSPS

/***
* Shoutouts:
* 
* Bytecode origin https://www.reddit.com/r/ethereum/comments/6ic49q/any_assembly_programmers_willing_to_write_a/dj5ceuw/
* Modified version of Vitalik's https://www.reddit.com/r/ethereum/comments/6c1jui/delegatecall_forwarders_how_to_save_5098_on/
* Credits to Jorge Izquierdo (@izqui) for coming up with this design here: https://gist.github.com/izqui/7f904443e6d19c1ab52ec7f5ad46b3a8
* Credits to Stefan George (@Georgi87) for inspiration for many of the improvements from Gnosis Safe: https://github.com/gnosis/gnosis-safe-contracts
* 
* This version has many improvements over the original @izqui's library like using REVERT instead of THROWing on failed calls.
* It also implements the awesome design pattern for initializing code as seen in Gnosis Safe Factory: https://github.com/gnosis/gnosis-safe-contracts/blob/master/contracts/ProxyFactory.sol

tjade273

function log2(uint x) returns (uint y){
   assembly {
        let arg := x
        x := sub(x,1)
        x := or(x, div(x, 0x02))
        x := or(x, div(x, 0x04))
        x := or(x, div(x, 0x10))
        x := or(x, div(x, 0x100))
        x := or(x, div(x, 0x10000))
        x := or(x, div(x, 0x100000000))