You are making two functions calls in the second loop, vs one in the first. If the result of read() could be checked for eof, then you would remove one call. Also, since the branch is so easily predicted, I would be surprised if there is much of a performance hit once the second call is removed.

If you see a 50% speed-up in the above code, I question what read is doing and the implementation of eof(). I would expect read() to dominate the if statement unless eof is extremely expensive. I have written dozens of read()/eof() functions over the years and read() always dominates because the read involves copying memory and/or making OS calls, etc., while eof() is a simple comparison. So if read() dominates runtime, example 1 and 2 above should not be anywhere close to 50% different.