[Dwarf-Discuss] DWARF piece questions

Michael Eager eager at eagercon.com
Thu Jan 26 18:48:45 PST 2017

On 01/26/2017 05:19 PM, Cary Coutant wrote:
>> On the other hand, using bit or byte numbering, or left or right, seem to
>> depend on who is drawing a diagram and where they start numbering.  There
>> is more consistency in description among big-endian architectures than among
>> little-endian, but there's clearly no hard and fast rule.
> Funny, I was going to make the opposite claim: I've seen big-endian
> architectures with architecture manuals where bits are numbered left
> to right, consistent with bytes in a word, and others where the bits
> are numbered right to left, consistent with the power-of-two bit
> value, often numbered that way to make the descriptions of shift and
> bit-extract instructions internally consistent. On the other hand, I
> can't recall ever seeing a little-endian architecture whose manual
> numbered bits left to right.

PowerPC numbers bits MSB to LSB (left to right).  Conceptually it is
both big- and little-endian, if less so in common practice.

Xilinx MicroBlaze, originally big-endian, numbers bits left to right.
Most MB applications are now little-endian, to be compatible with ARM.

But I'll give you that point, bit numbering is inconsistent in both
big- and litle-endian architectures.

Michael Eager	 eager at eagercon.com
1960 Park Blvd., Palo Alto, CA 94306  650-325-8077

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