Andrew Lentvorski wrote:
> Jan Decaluwe wrote:
>
>> This is an essay that I wanted to write for a long time.
>> It describes what I think is wrong with integer arithmetic
>> in VHDL and Verilog, and why MyHDL provides a solution.
>>
>> Before releasing it to the general public, I'm interested
>> to hear what you think about it.
>>
>> http://www.jandecaluwe.com/hdldesign/counting.html
>>
>
> The essay sums up some of my gripes about the mishmash that is the whole
> abstract behavior of numbers problem. Nicely done. I know that I'll
> point more than a few newbies at it.
>
>
> I do have a bit of a gripe about statements like:
> "This situation would not persist without the widespread support of the
> designer community."
>
> Ummmmm, no. Most of the designers I know of hate the way a *lot* of
> things are done in Verilog and VHDL. Would we be using MyHDL if that
> were not the case? ;) However, an individual designer has very limited
> options to push back into these standards. See SystemVerilog, for
> example. EDA vendors have a high incentive and large resources to
> push/implement what is *profitable* to them--usefulness to the the user
> is an orthogonal consideration.
>
>
> However, if we're talking about abstract behavior of numbers, how about
> some fixed-point support? One of the nice things about VHDL is the
> ability to specify negative indicies that align with negative powers of
> 2. Verilog doesn't (or at least didn't) provide even this level of support.
>
+1
I would love to have a fixed-point type with arthimetic support. It is
a lot of book keeping and quite messy syntactically to add
/subtract/multiply two fixed point numbers, especially when they have
different fractional widths. When adding/subtracting, for example, you
have to zero pad the LSBs until the decimal points line up prior to
adding. Something like (in verilog):
wire [DATA_WIDTH-1:0] result = data1 + { data2, {FRAC_WIDTH1 -
FRAC_WIDTH2 {1'b0}};
Furthermore, you have to know up front which one is going to have more
fractional bits so that you can pad the appropriate one.
Lane
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