Another option could be to borrow a trick from floating point, and have a separate status register with bits that represent the kinds of errors encountered. Bef

Another option could be to borrow a trick from floating point, and have a separate status register with bits that represent the kinds of errors encountered. Before a many-step calculation, software could clear these bits, and if any of them is set after the calculation, there was an error somewhere. Of course, since you don't have a NaN, you have to specify the bit pattern which will be returned by each kind of failing operation (like RISC-V does with integer divide by zero). That doesn't help if the result could be partially valid, but if a "square root of minus one" or similar anywhere in the calculation means the result is invalid (and would be a NaN under floating point), sticky error bits in a status register could be sufficient.