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Ivan Godard
Post count: 689

There are no condition codes as such; it’s kind of hard to do when you can have half-a-dozen CC-setting operations in each instruction, although some architectures try, using multiple CC registers.

To have the effect of a carry bit, if you know that no argument was a Nar and you do an addux and get a NaR out, then you must have gotten an overflow, but that’s pretty kludgy. Or you could do an adduw and test the first bit in the extended data, but that’s pretty kludgy too.

However, there is an alternative: the current operation set includes addc and subc, with two results: a wrapped value and a carry/borrow. It is not clear whether these ops will stay around though; the only use is in an arbitrary-precision library, and for quad arithmetic on members that don’t support native quad; neither of these seem that common, and it’s not clear that the ops (which would have two-cycle latency) are worth it.

We expect a general triage of the operations set later in the process of an FPGA implementation.