BCD calculators

[jte]

(08-19-2021 02:05 AM)Paul Dale Wrote:  There has been some movement towards including the IEEE 754 floating point decimals in hardware. Mostly by IBM.

Yes… when I was first reading above, one of the first architectures that popped into my mind was the Power ISA. (… and then I experienced the tiniest chagrin when reading “zSeries” )

Even with “hardware support”, some (non-ancient, binary) FPUs do punt when encountering some of the less-common floating-point values (e.g., denormalized numbers) — either through microcode assist or software assist. You can see this by running timing benchmarks. (I haven’t tried running these sorts of tests on the latest CPUs.)

Quote:It hasn’t trickled down to embedded platforms but would be nice if/when it does. The standard defines two representations neither of which is BCD.

It’s interesting seeing the distinction being drawn between BCD and DPD; a detail I’d be prone to overlooking in casual discussions. (Given how efficiently hardware can convert between BCD and DPD. I might throw in something like “more space-efficient encoding” to clarify it’s not exactly BCD.) My guess is that decimal FPU hardware doesn’t directly calculate with DPD. (Even if in DPD in registers, I’d guess it’s converted to and from another format before and after the actual calculation is performed.)

It will be interesting when / if decimal arithmetics arrive in embedded CPUs. I’m guessing the transistor budget considerations are quite different (for embedded CPUs as compared to things like Power CPUs).