gen_primes.py

#!/usr/bin/env python3

def gen_primes():
    D = {}
    q = 2
    
    while True:
        if q not in D:
            yield q
            D[q * q] = [q]
        else:
            for p in D[q]:
                D.setdefault(p + q, []).append(p)
            del D[q]
        
        q += 1

max = 2400000

print('#include <stdio.h>\n')
print('int main() {')
print('\tlong n = -1;\n')
print('\tprintf("Max number to calculate to?\\n> ");')
print('\tscanf("%ld", &n);\n')
print('\tif (n < 0 || n > 2400000) {')
print('\t\tprintf("%ld is not in range [0, 2400000]\\n", n);')
print('\t\treturn 1;')
print('\t}\n')

print('\tvoid *jmp_table[] = {')
for i in range(0, max + 1):
    print(f'\t\t&&label_{i},')

print('\t};\n')

print('\tgoto *jmp_table[n];\n')

nums = {}

i = 0
it = gen_primes()
while i <= max:
    prime = next(it)
    while i < prime:
        nums[i] = False
        i += 1
    nums[i] = True
    i += 1

for i in range(max, -1, -1):
    print(f'\tlabel_{i}:')
    if nums[i]:
        print(f'\tprintf("{i} ");')

print('\n\tprintf("\\nGoodbye!\\n");')
print('}')