findprimes.c

#include <math.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>

#define ARGLEN  10
#define true    1
#define false   !true


int main(int argc, char** argv)
{
    uint8_t  notPrime;
    uint32_t count = 0;
    uint64_t start, end, divInt, i;

    uint64_t * primes;

    long double divFloat, current, currentMax, testPrime;

    // ensure null-terminated
    char *startArg = malloc(ARGLEN + 1); memset(startArg, 0, ARGLEN + 1);
    char *lastValid = malloc(ARGLEN + 1); memset(lastValid, 0, ARGLEN + 1);

    if (argc <= 1)
    {
        start = 3;
    }
    else
    {
        startArg = (char*)memcpy(startArg, argv[1], ARGLEN * sizeof(char));
        start = (uint64_t)strtoll(startArg, &lastValid, 10);

        if (strlen(argv[1]) > ARGLEN)
        {
            printf("warning: starting number truncated\n");
        }

        if (strcmp(startArg, lastValid) == 0)
        {
            printf("%s is an invalid number\n", startArg);
            return 1;
        }
    }

    if (argc <= 2)
    {
        end = 0xFFFFFFFFFFFFFFFF;
    }
    else
    {
        startArg = (char*)memcpy(startArg, argv[2], ARGLEN * sizeof(char));
        end = (uint64_t)strtoll(startArg, &lastValid, 10);

        if (strlen(argv[1]) > ARGLEN)
        {
            printf("warning: starting number truncated\n");
        }

        if (strcmp(startArg, lastValid) == 0)
        {
            printf("%s is an invalid number\n", startArg);
            return 1;
        }
    }

    if (start >= end)
    {
        printf("The interval [%lu, %lu] is empty, aborting", start, end);
        return 2;
    }

    printf("Starting at number \"%lu\", ending at number \"%lu\"\n", start, end);
    current = (long double)start;
    primes = malloc(((end - start) + 1) * sizeof(uint64_t));

    primes[0] = 2;

    while (1)
    {
        currentMax = sqrtl(current);
        notPrime = false;

        for (i = 0; i < count; i++)
        {
            testPrime = primes[i];

            if (testPrime > currentMax) { break; }

            divFloat = current / testPrime;
            divInt = round(divFloat);

            //printf("%-20Lf %Lf %lu\n", i, divFloat, divInt);

            if ((long double)divInt == divFloat)
            {
                notPrime = true;
                break;
            }
        }

        if (!notPrime)
        {
            printf("%lu\n", (uint64_t)current);
            primes[++count] = current;
            /*
            printf("%-12lu", (uint64_t)current);


            if (!(count & 7))
            {
                printf("\n");
            }
            */
        }

        current++;

        if (current >= end) { break; }
    }
    printf("\n");
}