/* TomsFastMath, a fast ISO C bignum library.
 *
 * This project is meant to fill in where LibTomMath
 * falls short.  That is speed ;-)
 *
 * This project is public domain and free for all purposes.
 *
 * Tom St Denis, tomstdenis@gmail.com
 */
#include <tfm_private.h>

/* This is possibly the mother of all prime generation functions, muahahahahaha! */
int fp_prime_random_ex(fp_int *a, int t, int size, int flags, tfm_prime_callback cb, void *dat)
{
   unsigned char *tmp, maskAND, maskOR_msb, maskOR_lsb;
   int res, err, bsize, maskOR_msb_offset;

   /* sanity check the input */
   if (size <= 1 || cb == NULL || t <= 0 || t > FP_PRIME_SIZE) {
      return FP_VAL;
   }

   /* TFM_PRIME_SAFE implies TFM_PRIME_BBS */
   if (flags & TFM_PRIME_SAFE) {
      flags |= TFM_PRIME_BBS;
   }

   /* calc the byte size */
   bsize = (size>>3)+(size&7?1:0);

   /* we need a buffer of bsize bytes */
   tmp = malloc(bsize);
   if (tmp == NULL) {
      return FP_MEM;
   }

   /* calc the maskAND value for the MSbyte*/
   maskAND = 0xFF >> ((8 - (size & 7)) & 7);

   /* calc the maskOR_msb */
   maskOR_msb        = 0;
   maskOR_msb_offset = (size - 2) >> 3;
   if (flags & TFM_PRIME_2MSB_ON) {
      maskOR_msb     |= 1 << ((size - 2) & 7);
   } else if (flags & TFM_PRIME_2MSB_OFF) {
      maskAND        &= ~(1 << ((size - 2) & 7));
   }

   /* get the maskOR_lsb */
   maskOR_lsb         = 1;
   if (flags & TFM_PRIME_BBS) {
      maskOR_lsb     |= 3;
   }

   do {
      /* read the bytes */
      if (cb(tmp, bsize, dat) != bsize) {
         err = FP_VAL;
         goto error;
      }

      /* work over the MSbyte */
      tmp[0]    &= maskAND;
      tmp[0]    |= 1 << ((size - 1) & 7);

      /* mix in the maskORs */
      tmp[maskOR_msb_offset]   |= maskOR_msb;
      tmp[bsize-1]             |= maskOR_lsb;

      /* read it in */
      fp_read_unsigned_bin(a, tmp, bsize);

      /* is it prime? */
      res = fp_isprime_ex(a, t);
      if (res == FP_NO) continue;

      if (flags & TFM_PRIME_SAFE) {
         /* see if (a-1)/2 is prime */
         fp_sub_d(a, 1, a);
         fp_div_2(a, a);

         /* is it prime? */
         res = fp_isprime_ex(a, t);
      }
   } while (res == FP_NO);

   if (flags & TFM_PRIME_SAFE) {
      /* restore a to the original value */
      fp_mul_2(a, a);
      fp_add_d(a, 1, a);
   }

   err = FP_OKAY;
error:
   free(tmp);
   return err;
}

/* $Source$ */
/* $Revision: 0.13.0 $ */
/* $Date: 2015-08-11 23:26:06 +0200 $ */
