How large are header scalar values?

Question

The Yellow paper talks about "scalar values" in section 4.4 to describe block header fields. E.g.

difficulty: A scalar value corresponding to the dif- ficulty level of this block. This can be calculated from the previous block’s difficulty level and the timestamp; formally Hd.

How large (in bits) are scalar values? Are they fixed size, or variable size?

Answer 1

The header is defined here, and the 5 scalar values are *big.Int. These are arbitrary precision integers, so variable size.