c3-lang/libtommath/bn_mp_sqrt.c

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• Hash : 4e3f1344
  Author :
  Date : 2015-11-12T01:49:07
  

  provide tommath_private.h tommath.h contains declarations for the public part of the library. tommath_private.h contains the functions which are private to ltm and should not be exposed to the public.

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• bn_mp_sqrt.c

• #include <tommath_private.h>
  #ifdef BN_MP_SQRT_C
  /* 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, tstdenis82@gmail.com, http://libtom.org
   */
  
  /* this function is less generic than mp_n_root, simpler and faster */
  int mp_sqrt(mp_int *arg, mp_int *ret) 
  {
    int res;
    mp_int t1,t2;
  
    /* must be positive */
    if (arg->sign == MP_NEG) {
      return MP_VAL;
    }
  
    /* easy out */
    if (mp_iszero(arg) == MP_YES) {
      mp_zero(ret);
      return MP_OKAY;
    }
  
    if ((res = mp_init_copy(&t1, arg)) != MP_OKAY) {
      return res;
    }
  
    if ((res = mp_init(&t2)) != MP_OKAY) {
      goto E2;
    }
  
    /* First approx. (not very bad for large arg) */
    mp_rshd (&t1,t1.used/2);
  
    /* t1 > 0  */ 
    if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) {
      goto E1;
    }
    if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) {
      goto E1;
    }
    if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) {
      goto E1;
    }
    /* And now t1 > sqrt(arg) */
    do { 
      if ((res = mp_div(arg,&t1,&t2,NULL)) != MP_OKAY) {
        goto E1;
      }
      if ((res = mp_add(&t1,&t2,&t1)) != MP_OKAY) {
        goto E1;
      }
      if ((res = mp_div_2(&t1,&t1)) != MP_OKAY) {
        goto E1;
      }
      /* t1 >= sqrt(arg) >= t2 at this point */
    } while (mp_cmp_mag(&t1,&t2) == MP_GT);
  
    mp_exch(&t1,ret);
  
  E1: mp_clear(&t2);
  E2: mp_clear(&t1);
    return res;
  }
  
  #endif
  
  /* $Source$ */
  /* $Revision$ */
  /* $Date$ */
  

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