return (*C.uint8_t)(unsafe.Pointer(&b[0]))
}

const wordBytes = bits.UintSize / 8

func bigToBN(x BigInt) *C.GO_BIGNUM {
	return C._goboringcrypto_BN_le2bn(wbase(x), C.size_t(len(x)*wordBytes), nil)
}

func bytesToBN(x []byte) *C.GO_BIGNUM {
	return C._goboringcrypto_BN_bin2bn((*C.uint8_t)(&x[0]), C.size_t(len(x)), nil)
}

func bnToBig(bn *C.GO_BIGNUM) BigInt {

	nid, err := curveNID(curve)
	if err != nil {
		return nil, err
	}
	key := C._goboringcrypto_EC_KEY_new_by_curve_name(nid)
	if key == nil {
		return nil, fail("EC_KEY_new_by_curve_name")
	}
	b := bytesToBN(bytes)
	ok := b != nil && C._goboringcrypto_EC_KEY_set_private_key(key, b) != 0
	if b != nil {
		C._goboringcrypto_BN_free(b)
	}
	if !ok {
		C._goboringcrypto_EC_KEY_free(key)