Re: [myhdl-list] [PATCH 1 of 2 V3] intbv: add support for negative indexes and slice limits

[Ben <ben...@gm...>]

Hi Angel,

Other than a preliminary discussion on the topic, and about why this
feature is interesting, this patch should also greatly benefit from
tests.

While I wasn't able to get the conversion tests running on my system
either (vlog, vcom, ... missing), the "core" one do work fine (once
you installed pytest, and set the PYTHONPATH in the Makefiles). Could
you look at this ?

Stylistic remark inlined.

Regards,
Benoît.

On Sun, Oct 14, 2012 at 12:54 AM, Angel Ezquerra
<ang...@gm...> wrote:
> # HG changeset patch
> # User Angel Ezquerra <ang...@gm...>
> # Date 1350077846 -7200
> # Branch 0.8-dev
> # Node ID c641c1ed333d6d03d9cee4a63df5111fe98574c8
> # Parent  6f6571dbd495f197531f0406763ff10e4ce3b3ee
> intbv: add support for negative indexes and slice limits
>
> Negative indexes are supported on regular python lists. They are very useful
> when you want to refer to a position from the end of the list. This same concept
> can be applied to intbv indexes and slices. Supporting negative indexes reduces
> the need to use the len() function to calculate a position from the MSB of the
> intbv.
>
> Note that converting negative indexes is not supported yet.
>
> diff --git a/myhdl/_intbv.py b/myhdl/_intbv.py
> --- a/myhdl/_intbv.py
> +++ b/myhdl/_intbv.py
> @@ -127,11 +127,15 @@
>                  j = 0
>              j = int(j)
>              if j < 0:
> -                raise ValueError, "intbv[i:j] requires j >= 0\n" \
> -                      "            j == %s" % j
> +                j = self._nrbits + j
> +                if j < 0:
> +                    raise ValueError, "intbv[i:j] requires j >= 0\n" \
> +                        "            j == %s" % j

The extra indent is not needed over there, and the error message could
benefit from clarification.

>              if i is None: # default
>                  return type(self)(self._val >> j)
>              i = int(i)
> +            if i < 0:
> +                i = self._nrbits + i
>              if i <= j:
>                  raise ValueError, "intbv[i:j] requires i > j\n" \
>                        "            i, j == %s, %s" % (i, j)
> @@ -139,6 +143,8 @@
>              return res
>          else:
>              i = int(key)
> +            if i < 0:
> +                i = self._nrbits + i
>              res = bool((self._val >> i) & 0x1)
>              return res
>
> @@ -153,14 +159,18 @@
>                  j = 0
>              j = int(j)
>              if j < 0:
> -                raise ValueError, "intbv[i:j] = v requires j >= 0\n" \
> -                      "            j == %s" % j
> +                j = self._nrbits + j
> +                if j < 0:
> +                    raise ValueError, "intbv[i:j] = v requires j >= 0\n" \
> +                        "            j == %s" % j
>              if i is None: # default
>                  q = self._val % (1L << j)
>                  self._val = val * (1L << j) + q
>                  self._handleBounds()
>                  return
>              i = int(i)
> +            if i < 0:
> +                i = self._nrbits + i
>              if i <= j:
>                  raise ValueError, "intbv[i:j] = v requires i > j\n" \
>                        "            i, j, v == %s, %s, %s" % (i, j, val)
> @@ -174,6 +184,8 @@
>              self._handleBounds()
>          else:
>              i = int(key)
> +            if i < 0:
> +                i = self._nrbits + i
>              if val == 1:
>                  self._val |= (1L << i)
>              elif val == 0:
>
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