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[Chisel/Scala] Introduce decimal point data


What I want to do

I want to introduce decimal point data (float in other languages).

The background is that I'm trying to set up a performance counter in a self-designed CPU circuit, and I want to express it in a decimal instead of an integer. (For example, when measuring the "number of cycles per command," the meaning is completely different whether it is 1 or 1.9.)



Problem

It would be nice if Chisel had something like a floating point data type, but it doesn't currently exist.

There used to be a FixedPoint type that represented floating point numbers, and when I searched the internet I found this method, but it seems that it has now been deprecated ( reference ).



Countermeasure

Since there is no other choice, I tried with only integer types. This time, the purpose is to display the calculation results on the screen rather than to calculate decimal numbers, so

  • When calculating, store the value multiplied by 10 in an integer type.

  • When displaying, calculate and display the integer part and decimal part separately.

like this

val cpi10 = Mux(instCount === 0.U, 0.U, cycleCount * 10.U / instCount)
printf(p"CPI: ${cpi10/10.U}.${cpi10%10.U}\n")

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