gmpy_cffi is slow
As you can see, the time taken to initialize an mpz instance is about 10x slower under gmpy_cffi when compared to gmpy.
The gmpy mpz initialisation code uses the CPython internals to access the raw bits storing the value of a python integer (or long).
In comparison, gmpy_cffi converts the number to a hex string and then uses
mpz_set_str with base 16 to set the GMP mpz value
I’ve tried other methods such as using bit twiddling to break the python int into an array of C ints and then using mpz_import, but it was slower than using hex
The conversion from python long to gmp mpz is by far the main reason why initializing mpzs in gmpy_cffi is so slow, but there isn’t really an obvious way to improve on this.
Perhaps cffi could provide a fast method for converting python longs to an array of C ints, but I doubt there’s a huge demand for that right now.
We’re within a factor of 10 of evil low level C hackery. For now that will have to do.