Add `/usr/local` to IDIRS and LDIRS

Ditch custom `sig128_t` type in favour of `__int128`

Use entire words for sieve of eratosthenes

Add Makefile for riscv

Make a custom 128 bit type for storing MPFR significand

Add an executable for Sieve of Eratosthenes pi function

Get raw significand bytes out of MPFR

MPFR Extract fractional part by subtracting floor

Change `mpfr_set_d` to `mpfr_set_ui`

Implement Sieve of Eratosthenes for generating primes

Breakout main

Primes need not be doubles

Test out hex printing with MPFR

Test MPFR

Computing SHA-224, SHA-256 constants

Cache bit setting for mersenne calculation

Convert Lucas Lehmer to gmp

Use `PRIu64' for printing `uint64_t` type values

Add README

Fix ``M_61 is not prime'' with GMP