This is the wrong list to ask such a question, but I'll answer it
anyway since the answer might be of general interest.
There is a wonderful book "Hacker's Delight" by Henry S. Warren Jr.,
http://www.awprofessional.com/bookstore/product.asp?
isbn=0201914654&redir=1&rl=1
In some ways it can be thought of as building on the HAKMEM memos of
MIT; it has a Forward by Guy Steele. The book has a lot of fast
bit-twiddling (unbelievably, "twiddling" just passed my Mac's
spell-checker) algorithms for operating at the machine word level and
gives the answer to your question in Chapter 1.
Assuming that overflow of signed integer arithmetic wraps (and what gcc
flag do I have to set to assume this?) then here is the algorithm to
multiply x and y with overflow detection.
if y = 0 then
result = 0
else if y = -1 then
if x = the_minimum_negative_value then
result = overflow
else
result = -x
else
let z = x * y;
if z / y = x then
result = z
else
result = overflow
Brad
