isPowOfTen.yul

isPowOfTen.yul

// https://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup
function isPowerOfTen(uint256 x) public pure returns (bool result) {
    assembly {
        let dict := 0x00011c021d0e18031e16140f191104081f1b0d17151310071a0c12060b050a09

        let zeroes := 0
        for { let offset := 0 } lt(offset, 256) { offset := add(offset, 32) } {
            let v := and(shr(offset, x), 0xffffffff)

            switch v
            case 0 {
                zeroes := add(zeroes, 32)
            }
            default {
                zeroes := add(zeroes, byte(shr(27, mul(and(v, sub(0, v)), 0x077CB531)), dict))
            }
        }

        result := eq(shr(zeroes, x), pow(5, zeroes)) // todo: use table of powers
    }
}