Re: [myhdl-list] [PATCH 0 of 2 RFC] Add support for negative indexes

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

On 10/13/2012 02:12 AM, Angel Ezquerra wrote:
> Python lists have a natural way to access list itemps from the end of
> the list, which is to use negative indexes. These patches add this
> functionality to MyHDL.
>
> The first patch adds negative index and slice limit support to the
> intbv class. I think this first patch is probably right and not very
> controversial

intbv's are dual in nature - bit sequence but also integer interpretation.

indexing is at the intersection of the two. An index corresponds
to a bit position, but also to the power of the bit when
expanding the integer in a sum of powers of 2. To match
the natural way of writing numbers, intbv slicing is already
totally different from any standard python sequence: the direction
is reversed.

Personally, I haven't seen much need to enhance intbv bit indexing
to match what you can do with sequences like lists. However, there
is a very good reason to stress the power of two interpretation:
when we add a fixbv type, it would be natural to use the same
interpretation. Negative indices would represent fractional bits.
It also seems natural that the intbv would like a subtype of
a general fixbv type.

Therefore, I propose to keep intbv indexing like it is.


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