Fixed point optimization

I see, I remember someone else also reported a similar situation before. This is indeed strange. Try using short or char for "output" and "out" and see what happens. I would expect using int for these variables might "promote" all the multiplications to int, since the output is int. Furthermore, you can take a look at "Intel FPGA SDK for OpenCL Best Practices Guide, Section 3.3.1 Floating-Point versus Fixed-Point Representations" and follow the guidelines to mask out bits to see if you can get the desired results. If none helped, I recommend opening a ticket with Altera directly.