--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/bn_mp_prime_random_ex.c	Mon May 31 18:23:46 2004 +0000
@@ -0,0 +1,118 @@
+/* LibTomMath, multiple-precision integer library -- Tom St Denis
+ *
+ * LibTomMath is a library that provides multiple-precision
+ * integer arithmetic as well as number theoretic functionality.
+ *
+ * The library was designed directly after the MPI library by
+ * Michael Fromberger but has been written from scratch with
+ * additional optimizations in place.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ * Tom St Denis, [email protected], http://math.libtomcrypt.org
+ */
+#include <tommath.h>
+
+/* makes a truly random prime of a given size (bits),
+ *
+ * Flags are as follows:
+ * 
+ *   LTM_PRIME_BBS      - make prime congruent to 3 mod 4
+ *   LTM_PRIME_SAFE     - make sure (p-1)/2 is prime as well (implies LTM_PRIME_BBS)
+ *   LTM_PRIME_2MSB_OFF - make the 2nd highest bit zero
+ *   LTM_PRIME_2MSB_ON  - make the 2nd highest bit one
+ *
+ * You have to supply a callback which fills in a buffer with random bytes.  "dat" is a parameter you can
+ * have passed to the callback (e.g. a state or something).  This function doesn't use "dat" itself
+ * so it can be NULL
+ *
+ */
+
+/* This is possibly the mother of all prime generation functions, muahahahahaha! */
+int mp_prime_random_ex(mp_int *a, int t, int size, int flags, ltm_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 || t <= 0) {
+      return MP_VAL;
+   }
+
+   /* LTM_PRIME_SAFE implies LTM_PRIME_BBS */
+   if (flags & LTM_PRIME_SAFE) {
+      flags |= LTM_PRIME_BBS;
+   }
+
+   /* calc the byte size */
+   bsize = (size>>3)+(size&7?1:0);
+
+   /* we need a buffer of bsize bytes */
+   tmp = OPT_CAST(unsigned char) XMALLOC(bsize);
+   if (tmp == NULL) {
+      return MP_MEM;
+   }
+
+   /* calc the maskAND value for the MSbyte*/
+   maskAND = 0xFF >> (8 - (size & 7));
+
+   /* calc the maskOR_msb */
+   maskOR_msb        = 0;
+   maskOR_msb_offset = (size - 2) >> 3;
+   if (flags & LTM_PRIME_2MSB_ON) {
+      maskOR_msb     |= 1 << ((size - 2) & 7);
+   } else if (flags & LTM_PRIME_2MSB_OFF) {
+      maskAND        &= ~(1 << ((size - 2) & 7));
+   }
+
+   /* get the maskOR_lsb */
+   maskOR_lsb         = 0;
+   if (flags & LTM_PRIME_BBS) {
+      maskOR_lsb     |= 3;
+   }
+
+   do {
+      /* read the bytes */
+      if (cb(tmp, bsize, dat) != bsize) {
+         err = MP_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 */
+      if ((err = mp_read_unsigned_bin(a, tmp, bsize)) != MP_OKAY)     { goto error; }
+
+      /* is it prime? */
+      if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY)           { goto error; }
+
+      if (flags & LTM_PRIME_SAFE) {
+         /* see if (a-1)/2 is prime */
+         if ((err = mp_sub_d(a, 1, a)) != MP_OKAY)                    { goto error; }
+         if ((err = mp_div_2(a, a)) != MP_OKAY)                       { goto error; }
+ 
+         /* is it prime? */
+         if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY)        { goto error; }
+      }
+   } while (res == MP_NO);
+
+   if (flags & LTM_PRIME_SAFE) {
+      /* restore a to the original value */
+      if ((err = mp_mul_2(a, a)) != MP_OKAY)                          { goto error; }
+      if ((err = mp_add_d(a, 1, a)) != MP_OKAY)                       { goto error; }
+   }
+
+   err = MP_OKAY;
+error:
+   XFREE(tmp);
+   return err;
+}
+
+