pow(int, int, fmpz) is always 1

[haru-44]

In python-flint==0.4.4.

>>> from flint import fmpz
>>> pow(2, 5, 1000)
32
>>> pow(2, 5, fmpz(1000))
1
>>> pow(2, fmpz(5), fmpz(1000))
32

[oscarbenjamin]

Looks like the code here should be checking the type of s:

python-flint/src/flint/types/fmpz.pyx

Lines 362 to 371 in 98c2883

	def __pow__(s, t, m):
	cdef fmpz_struct tval[1]
	cdef fmpz_struct mval[1]
	cdef int ttype = FMPZ_UNKNOWN
	cdef int mtype = FMPZ_UNKNOWN
	cdef int success
	u = NotImplemented
	ttype = fmpz_set_any_ref(tval, t)
	if ttype == FMPZ_UNKNOWN:
	return NotImplemented

I hadn't contemplated that __pow__(s, t, m) might be called with s not being an fmpz. At this line s will be an int (PyLong):

python-flint/src/flint/types/fmpz.pyx

Line 405 in 98c2883

fmpz_powm((<fmpz>u).val, (<fmpz>s).val, tval, mval)

Presumably the bytes there look like a 1 as an fmpz_t.

The fix is that the s argument should be handled in the same way as the t argument.

[oscarbenjamin]

Thanks for the bug report. This will be fixed in the next release.

[haru-44]

Thanks for the correction.