Re: [myhdl-list] essay about integer arithmetic

[Neal B. <ndb...@gm...>]

Michael Baxter wrote:

> IMHO, though informed with years of hardware implementation experience,
> automating bit-widths should be 100% a non-goal. It should never be done
> under any circumstances whatsoever.
> 
> IMHO, this is a serious failing of MyHDL.
> 
Actually, I agree.  That's why I wrote about my c++ approach to fixed-pt 
integers.  There, the approach is:

For unary op, the output size is same as input
For binary op, the 2nd operand is converted to the first, then the output 
size is same as input

(Actually, fixed-pt has 2 attributes: a number of integer bits and a number 
of frac bits, or equivalently a size and a binary point)

If you want to multiply 8bit x 8bit and result in 16bit, what you do in 
convert both operands to 16bit first.

The reason is, I really don't think it's possible to have a machine 
correctly deal with these issues in all cases.

Perhaps more important, though, is the question of even if it is possible 
for some kind of algorithm to decide the bit widths, is this really 
desirable?  I'm not sure about that.  Maybe the designer really should be 
aware of these details.