Python list slicing translation

[wizard97]

Translation does not work for ranges involving negative indices. The pythonic way to get the last element in a list is x[-1]. This translates fine. However, the semantics of list slicing involving negative indices are not translated properly and you get a verilator error about backwards bit ordering:

For example, both of these fail to translate:

• x[:-1] (get everything up to the last element)
• x[0:-1]

[-2:0] Range extract has backward bit ordering, perhaps you wanted [0:-2]

A common example of where you would want to do list slicing such as this is dealing with signed numbers, where you want to extract the sign bit x[-1] as well as everything else x[:-1]