Craig McQueen pyt...@craig.mcqueen.id.au added the comment:
So this has been rejected I see. Too bad, since I stub my metaphorical toe on
this issue from time to time. Just for the record, here is an example:
http://stackoverflow.com/questions/4130936/perfect-hash-function/6976723#6976723
Mark Dickinson dicki...@gmail.com added the comment:
Interesting. I agree that that looks like a case where it would be desirable
for a -n to do a n.
By the way, I don't think your formula is quite correct: your crc is going to
grow unboundedly as extra data bytes come in. I suspect that
Mark Dickinson dicki...@gmail.com added the comment:
One other thought: you could always compute the expression
crc (crc_width - 8)
as
crc 8 crc_width
Since you're computing crc 8 anyway, this doesn't increase the operations
count, so probably wouldn't significant impact
Craig McQueen pyt...@craig.mcqueen.id.au added the comment:
Thanks, good points. I'm thinking with a C background and the fixed-width data
types. The 0xFF could be needed if the data_byte is actually a larger number
and you need to ensure only the lowest 8 bits are set. Or, if there is some
Craig McQueen pyt...@craig.mcqueen.id.au added the comment:
To complete that thought...
Since crc 8 could bump the calculation into long territory, for that final
mask I guess I'd want to mask and then shift. I.e. rather than
crc_mask = ((1 crc_width) - 1)
crc = (...) ^ ((crc 8)
Craig McQueen pyt...@craig.mcqueen.id.au added the comment:
Just for the record... here is a relevant use case...
I'm working on some code for calculating CRCs, and hope to support any CRC
width, including CRC-5. This involves, among the calculations:
crc (crc_width - 8)
The complete
Mark Dickinson dicki...@gmail.com added the comment:
Rejecting this due to:
- no activity for almost 4 years
- lack of positive responses
Also, I'm -1 on this change: for me, a x n that silently becomes
x -n when n is negative would cause more harm than good. In most
of my uses, left
Changes by Mark Dickinson dicki...@gmail.com:
--
nosy: +marketdickinson
___
Python tracker rep...@bugs.python.org
http://bugs.python.org/issue1205239
___
___
