First nonzero entry in an array of unknown size

An array of unknown length consists of a run of zeros followed by nonzero entries. How do you locate the first nonzero entry efficiently?

Exponential (galloping) search, then binary search: $O(\log k)$ for answer position $k$. Probe indices $1,2,4,8,\dots$ until a nonzero is found at $2^m$; the first nonzero then lies in $(2^{m-1},2^m]$, which binary search pins down in $O(m)$ further probes. No knowledge of the array length is required.