I'm working on PEP 3101, Advanced String Formatting. About the only
built-in numeric formatting I have left to do is for converting a
PyLongOjbect to binary.
I need to know how to access the bits in a PyLong. After reading
longobject.c, I can figure it out. But I'm looking for something that
might be preferable to me poking around directly in ob_size and ob_digit[].
I'm looking for something along the lines of:
for (i = 0; i < _PyLong_NumBits(v); i++) {
// get i-th bit of v
}
I don't care if it's increasing or decreasing bits, I can handle either.
I realize the actual code will likely involve the 2 nested loops, but
logically this is what I need.
I can certainly do this myself, by looping over ob_digit and then over
each bit. But there's a comment in longintrepr.h that says the
internals are published only for marshal.c. Should I go ahead and
include longintrepr.h and loop over ob_digit myself, or is there some
other method? I really don't want to use _PyLong_AsByteArray, since I
don't want to do the copy.
If I'm missing some PyLongObject API, please let me know.
By the way, while doing this I noticed a bug in stringobject.c and
unicodeobject.c, relating to a missing check for 'G' precision. I'm not
sure if it could be a buffer overflow or not, without spending some more
time analyzing at it. But it seems like the potential is certainly
there. The bug is at http://python.org/sf/1673757 and a patch at
http://python.org/sf/1673759.
(I'll save my comments on how "approachable" python-dev is after I have
this question answered!)
Thanks for your time.
Eric.
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