crypto/external/bsd/heimdal/dist/lib/hcrypto/libtommath/bn_mp_sqrt.c

   1 /*      $NetBSD: bn_mp_sqrt.c,v 1.1.1.2 2014/04/24 12:45:31 pettai Exp $        */
   2
   3 #include <tommath.h>
   4 #ifdef BN_MP_SQRT_C
   5 /* LibTomMath, multiple-precision integer library -- Tom St Denis
   6  *
   7  * LibTomMath is a library that provides multiple-precision
   8  * integer arithmetic as well as number theoretic functionality.
   9  *
  10  * The library was designed directly after the MPI library by
  11  * Michael Fromberger but has been written from scratch with
  12  * additional optimizations in place.
  13  *
  14  * The library is free for all purposes without any express
  15  * guarantee it works.
  16  *
  17  * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
  18  */
  19
  20 /* this function is less generic than mp_n_root, simpler and faster */
  21 int mp_sqrt(mp_int *arg, mp_int *ret)
  22 {
  23   int res;
  24   mp_int t1,t2;
  25
  26   /* must be positive */
  27   if (arg->sign == MP_NEG) {
  28     return MP_VAL;
  29   }
  30
  31   /* easy out */
  32   if (mp_iszero(arg) == MP_YES) {
  33     mp_zero(ret);
  34     return MP_OKAY;
  35   }
  36
  37   if ((res = mp_init_copy(&t1, arg)) != MP_OKAY) {
  38     return res;
  39   }
  40
  41   if ((res = mp_init(&t2)) != MP_OKAY) {
  42     goto E2;
  43   }
  44
  45   /* First approx. (not very bad for large arg) */
  46   mp_rshd (&t1,t1.used/2);
  47
  48   /* t1 > 0  */
  49   if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) {
  50     goto E1;
  51   }
  52   if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) {
  53     goto E1;
  54   }
  55   if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) {
  56     goto E1;
  57   }
  58   /* And now t1 > sqrt(arg) */
  59   do {
  60     if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) {
  61       goto E1;
  62     }
  63     if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) {
  64       goto E1;
  65     }
  66     if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) {
  67       goto E1;
  68     }
  69     /* t1 >= sqrt(arg) >= t2 at this point */
  70   } while (mp_cmp_mag(&t1,&t2) == MP_GT);
  71
  72   mp_exch(&t1,ret);
  73
  74 E1: mp_clear(&t2);
  75 E2: mp_clear(&t1);
  76   return res;
  77 }
  78
  79 #endif
  80
  81 /* Source: /cvs/libtom/libtommath/bn_mp_sqrt.c,v  */
  82 /* Revision: 1.4  */
  83 /* Date: 2006/12/28 01:25:13  */