### diff libtommath/bn_mp_n_root.c @ 1436:60fc6476e044

Update to libtommath v1.0
author Matt Johnston Sat, 24 Jun 2017 22:37:14 +0800 5ff8218bcee9 8bba51a55704
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```--- a/libtommath/bn_mp_n_root.c	Sat Jun 24 17:50:50 2017 +0800
+++ b/libtommath/bn_mp_n_root.c	Sat Jun 24 22:37:14 2017 +0800
@@ -1,4 +1,4 @@
-#include <tommath.h>
+#include <tommath_private.h>
#ifdef BN_MP_N_ROOT_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
@@ -12,121 +12,19 @@
* The library is free for all purposes without any express
* guarantee it works.
*
- * Tom St Denis, [email protected], http://math.libtomcrypt.com
+ * Tom St Denis, [email protected], http://libtom.org
*/

-/* find the n'th root of an integer
- *
- * Result found such that (c)**b <= a and (c+1)**b > a
- *
- * This algorithm uses Newton's approximation
- * x[i+1] = x[i] - f(x[i])/f'(x[i])
- * which will find the root in log(N) time where
- * each step involves a fair bit.  This is not meant to
- * find huge roots [square and cube, etc].
+/* wrapper function for mp_n_root_ex()
+ * computes c = (a)**(1/b) such that (c)**b <= a and (c+1)**b > a
*/
int mp_n_root (mp_int * a, mp_digit b, mp_int * c)
{
-  mp_int  t1, t2, t3;
-  int     res, neg;
-
-  /* input must be positive if b is even */
-  if ((b & 1) == 0 && a->sign == MP_NEG) {
-    return MP_VAL;
-  }
-
-  if ((res = mp_init (&t1)) != MP_OKAY) {
-    return res;
-  }
-
-  if ((res = mp_init (&t2)) != MP_OKAY) {
-    goto LBL_T1;
-  }
-
-  if ((res = mp_init (&t3)) != MP_OKAY) {
-    goto LBL_T2;
-  }
-
-  /* if a is negative fudge the sign but keep track */
-  neg     = a->sign;
-  a->sign = MP_ZPOS;
-
-  /* t2 = 2 */
-  mp_set (&t2, 2);
-
-  do {
-    /* t1 = t2 */
-    if ((res = mp_copy (&t2, &t1)) != MP_OKAY) {
-      goto LBL_T3;
-    }
-
-    /* t2 = t1 - ((t1**b - a) / (b * t1**(b-1))) */
-
-    /* t3 = t1**(b-1) */
-    if ((res = mp_expt_d (&t1, b - 1, &t3)) != MP_OKAY) {
-      goto LBL_T3;
-    }
-
-    /* numerator */
-    /* t2 = t1**b */
-    if ((res = mp_mul (&t3, &t1, &t2)) != MP_OKAY) {
-      goto LBL_T3;
-    }
+  return mp_n_root_ex(a, b, c, 0);
+}

-    /* t2 = t1**b - a */
-    if ((res = mp_sub (&t2, a, &t2)) != MP_OKAY) {
-      goto LBL_T3;
-    }
-
-    /* denominator */
-    /* t3 = t1**(b-1) * b  */
-    if ((res = mp_mul_d (&t3, b, &t3)) != MP_OKAY) {
-      goto LBL_T3;
-    }
-
-    /* t3 = (t1**b - a)/(b * t1**(b-1)) */
-    if ((res = mp_div (&t2, &t3, &t3, NULL)) != MP_OKAY) {
-      goto LBL_T3;
-    }
-
-    if ((res = mp_sub (&t1, &t3, &t2)) != MP_OKAY) {
-      goto LBL_T3;
-    }
-  }  while (mp_cmp (&t1, &t2) != MP_EQ);
-
-  /* result can be off by a few so check */
-  for (;;) {
-    if ((res = mp_expt_d (&t1, b, &t2)) != MP_OKAY) {
-      goto LBL_T3;
-    }
-
-    if (mp_cmp (&t2, a) == MP_GT) {
-      if ((res = mp_sub_d (&t1, 1, &t1)) != MP_OKAY) {
-         goto LBL_T3;
-      }
-    } else {
-      break;
-    }
-  }
-
-  /* reset the sign of a first */
-  a->sign = neg;
-
-  /* set the result */
-  mp_exch (&t1, c);
-
-  /* set the sign of the result */
-  c->sign = neg;
-
-  res = MP_OKAY;
-
-LBL_T3:mp_clear (&t3);
-LBL_T2:mp_clear (&t2);
-LBL_T1:mp_clear (&t1);
-  return res;
-}
#endif

-/* \$Source: /cvs/libtom/libtommath/bn_mp_n_root.c,v \$ */
-/* \$Revision: 1.3 \$ */
-/* \$Date: 2006/03/31 14:18:44 \$ */
+/* \$Source\$ */
+/* \$Revision\$ */
+/* \$Date\$ */```