Re: [myhdl-list] essay about integer arithmetic

[Pieter <pie...@gm...>]

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

Hmm, for me it seems more logical that you should have 16 bits at the
left hand side of the assignment, to get a 16 bit result?

result_16 = op_a_8 * op_b_8;

2009/3/6 Neal Becker <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.
>
>
>
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Pieter Cogghe
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