Think I got it now

After a couple days fighting with this annoying overflow bug, I think I've managed to solve the problem. As you can see, some of the fixes are not very nice. It basically comes down to

• Adding explicit saturation (SATURATE) before 32-bit to 16-bit conversions.
• Scaling the signal up/down for some operations to avoid having to add saturation all over the place, especially in critical loops
• PSHR* is evil. Well, not quite but can you shot the danger in the PSHR32 definition?

The moral of the story: saturating isn't great, but it still beats overflowing!