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Since the solution is now specific to Python, I suggest continuing on
the pysqlite/APSW mailing list -
http://itsystementwicklung.de/cgi-bin/mailman/listinfo/list-pysqlite and
http://news.gmane.org/gmane.comp.python.db.pysqlite.user
Le Hyaric Bruno wrote:
> def blob_and(b1,b2):
> op1 = str(b1)
> op2 = str(b2)
> i = 0
> result = str()
> for char in op1:
> result = result + chr(ord(char) & ord(op2[i]))
> i = i + 1
> return buffer(result)
A few things wrong with this. There is no need to convert the
parameters to str - you can iterate over the buffers directly. That is
a horrendous way of doing string concatenation :-) Lastly this code
assumes that the parameters are exactly the same length - it will throw
an exception if b2 is shorter than b1 and ignore any part of b2 that is
longer than b1!
This code is closer to being conceptually right although there many
optimisations that can be done:
def blob_byte_and(left, right):
if left is None or right is None:
return 0
return left & right
def blob_byte_or(left, right):
if left is None: return right
if right is None: return left
return left | right
def blob_operate(method, left, right):
result=array.array('B', [a for a in map(method, [ord(x) for x in
left], [ord(y) for y in right])])
return buffer(result)
Example use: blob_operate(blob_byte_and, b1, b2)
If you are using Python 2.5+ then you can replace all the [] with ()
which will drastically cut down on memory usage. If performance is at
all an issue then you'd get the best bang for the buck by coding the
functions in C which won't require round trips through Python data types
or iteration over them.
Roger
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