On: MCS-48: The quest for 16-bit division on the 8-bit...

[phire]

Op is already in base 100 fixed point. I guess because that's what the sensor returns?

Though it might be smart to convert it to another format. Four nibbles of BCD would be ideal and the MCS-48 looks to have native support for it.

Thought you would need a custom version of shift by 4 that handles BCD.

Or simplify the equation to just adds:

    C2 = C + C
    C4 = C2 + C2
    C8 = C4 + C4
    C16 = C8 + C8
    Res = C16 + C2

[bonzini → phire]

If he's in base 100 and you multiply by 18 it's the same story: you are now in base 1000 and need a division to go back.

Converting from binary to BCD also needs division by constants, so again it's more or less the same.

[phire → bonzini]

Oh, right. I'm an idiot who forgot about the fixed point divide.

And yes, at some point you are going to need to do a divide by constant 10. It's unavoidable if you want a base 10 display. The option of using BCD to do calculations just lets you do that divide upfront, rather than at the end.