Memory leak

Some of the functions seem to leak memory. The test program below will continuously eat up more and more memory.

I suspect the issue is in your use of Py_BuildValue without freeing the char* afterwards. For example, in curvemath_mul, resultX and resultY are allocated but never freed.

#!/usr/bin/env python

import fastecdsa.curvemath, fastecdsa.curve, gc

sx = str(fastecdsa.curve.secp256k1.G[0])
sy = str(fastecdsa.curve.secp256k1.G[1])
sz = str(2**255-1)

while True:
    fastecdsa.curvemath.mul(sx, sy, sz, 'secp256k1')
    gc.collect()

[EggPool]

I gave this a try with current version and secp256k1: signature checks do not leak anymore, but signing does.

import gc, os, psutil
from hashlib import sha1

from fastecdsa import ecdsa
from fastecdsa.curve import secp256k1
from fastecdsa.keys import gen_keypair

message = b"Sample message for signature testing"
priv, pub = gen_keypair(secp256k1)

CHECK_SIGN = True
CHECK_VERIFY = False

process = psutil.Process(os.getpid())
r, s = ecdsa.sign(message, priv, hashfunc=sha1, curve=secp256k1)

while True:
    print(process.memory_info().rss)
    if CHECK_SIGN:
        for i in range(1000):
            r, s = ecdsa.sign(message, priv, hashfunc=sha1, curve=secp256k1)
        gc.collect()
    if CHECK_VERIFY:
        for i in range(1000):
            check_sig = ecdsa.verify((r, s), message, pub, curve=secp256k1, hashfunc=sha1)
        gc.collect()

[targon]

Attached patch fixes a number of memory leaks. After applying it, I can run curvemath.mul, curvemath.add and _ecdsa.verify in loops without increasing the memory usage.

memleak.patch.txt

Can you please check & merge?