#include <math.h>

FILE *FP = NULL;

static void seed_prng()

{

    int randBits = 0;

    int seedInt = 0;

    int toAdd = 0;

    int intSize = (8*(int)sizeof(int));

    int charSize = (8*(int)sizeof(char));

    if ( (!FP) && getenv("RANDOM_SEED") ) 

    {

        /* use the device specified by the user */

        FP = fopen(getenv("RANDOM_SEED"), "r");

    } else if (!FP) {

        /* use /dev/urandom for better (less predictable) seeding if available */

        FP = fopen("/dev/urandom", "r");

    }

    if (FP) 

    {

        while ( randBits < intSize ) {

            /* how many bits to read (maximum == bytes in a char) */

            toAdd = (intSize - randBits) > charSize ? charSize : (intSize - randBits);

            /* we could watch the fgetc() call for EOF and warn the user,

               but the user should know better than to provide a small pool */

            seedInt += ((int)fgetc(FP) % (int)pow(2,toAdd)) * (int)pow(2,randBits);

            randBits += toAdd;

        }

        (void) srand(seedInt);

        /* deliberately leave FP open in case seed_prng() is called again and

           FP behaves like a static file and always provides the same content;

           with devices like /dev/urandom and /dev/random, there would be bo reason

           not to fclose(FP) here */

    } else {

        fprintf(stderr,"Warning: weak salt generation!\n");

        fprintf(stderr,"For better security, install /dev/urandom or provide the name of a file or device\n");

        fprintf(stderr,"that can provide enough random data in the environment variable RANDOM_SEED\n",(intSize/8));

        (void) srand((int) time((time_t *) NULL));

    }

}

static void generate_salt(char *s, size_t size)

{

   static unsigned char tbl[] = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

   size_t i;

   int bitsUsed = 0;

   for (i = 0; i < size; ++i) {

       int idx = (int) (64.0 * rand() / (RAND_MAX + 1.0));

       bitsUsed += 6;

       s[i] = tbl[idx];

       /* re-seed the PRNG if already used an integer's worth of bytes, or if the next 

          loop iteration would use more than an int, since the seed for rand() is an int.

          This will only need to happen on platforms with integers less than 48 bits. */

       if ( (bitsUsed + 6) > (8*sizeof(int)) )

       {

           /* re-seed */

           (void)seed_prng();

           /* reset our counter */

           bitsUsed = 0;

       }

   }

}