Re: [myhdl-list] the path not taken

[Jan D. <ja...@ja...>]

Neal Becker wrote:
> I'm having a problem with this code:
> 
> def rnd (x, bits, output):
>     min_val = x.min
>     max_val = x.max
>     @always_comb
>     def rnd_logic():
>         if (bits < 1):
>             output.next = x
>         else:
>             y1 = intbv (int (x >> (bits-1)), min_val, max_val)
>             #y1 = intbv (int(x), min_val, max_val)
>             y2 = intbv (int (y1 + 1), min_val, max_val)
>             y3 = intbv (int (y2 >> 1), min_val, max_val)
>             output.next = y3
>     return rnd_logic
> 
> When translating to verilog:
> ValueError: negative shift count
> 
> If the commented line #y1 is used, no error.
> 
> So myhdl is complaining about neg shift count if bits < 1, even though I
> tried to eliminate that with the if (bits < 1).
> 
> What can I do?

I think the problem can be solved by making the code much
clearer at the same time. I would separate object contruction
from usage. Also, I would avoid using redundant objects and
constructors - now they look like ugly type conversions.

For example:

def rndn (x, bits, output):
    min_val = x.min
    max_val = x.max
    @always_comb
    def rnd_logic():
        y = intbv(0, min_val, max_val)
        if (bits < 1):
            output.next = x
        else:
            y[:] = x >> bits-1
            y += 1
            output.next = y >> 1
    return rnd_logic




-- 
Jan Decaluwe - Resources bvba - http://www.jandecaluwe.com
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