...if my math is bad. If I bought 1000 shares of INFN (assuming it's still available, and there were trades today) at $10.05, and it was traded in October for 7/8, or 875 shares of Umpqua at its current price, would I make a very fast 12%?
Smallbanks explained it well. I find that it's best for the lower volume investor, say one who purchases 1,000 shares or less, to deal with somewhat known conditions when those conditions can be established. For example, purchasing at "limit" prices. This approach reduces the number of unwelcome surprises.
If UMPQ is trading below $13 when the deal closes, then your 1000 shares of INFN become 827 (not, alas, 875)shares of UMPQ. If your cost for INFN is $10.05/share = $10,050, then you break even if UMPQ is at $12.16 or better.
But if UMPQ is trading above $13 when the deal closes, you get only 800 shares of UMPQ, and you then break even if UMPQ is at $12.57 or better.
As these are still lightly-traded stocks, the bid-asked spread and the commissions take a chunk of the possible profit on the deal.