kc3-lang/libtommath/mp_sqrt.c

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• Hash : 1cc289d2
  Author :
  Date : 2019-11-09T20:23:03
  

  better use of mp_isneg() and mp_iszero()

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• mp_sqrt.c

• #include "tommath_private.h"
  #ifdef MP_SQRT_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  /* this function is less generic than mp_n_root, simpler and faster */
  mp_err mp_sqrt(const mp_int *arg, mp_int *ret)
  {
     mp_err err;
     mp_int t1, t2;
  
     /* must be positive */
     if (mp_isneg(arg)) {
        return MP_VAL;
     }
  
     /* easy out */
     if (mp_iszero(arg)) {
        mp_zero(ret);
        return MP_OKAY;
     }
  
     if ((err = mp_init_copy(&t1, arg)) != MP_OKAY) {
        return err;
     }
  
     if ((err = mp_init(&t2)) != MP_OKAY) {
        goto LBL_ERR2;
     }
  
     /* First approx. (not very bad for large arg) */
     mp_rshd(&t1, t1.used/2);
  
     /* t1 > 0  */
     if ((err = mp_div(arg, &t1, &t2, NULL)) != MP_OKAY) {
        goto LBL_ERR1;
     }
     if ((err = mp_add(&t1, &t2, &t1)) != MP_OKAY) {
        goto LBL_ERR1;
     }
     if ((err = mp_div_2(&t1, &t1)) != MP_OKAY) {
        goto LBL_ERR1;
     }
     /* And now t1 > sqrt(arg) */
     do {
        if ((err = mp_div(arg, &t1, &t2, NULL)) != MP_OKAY) {
           goto LBL_ERR1;
        }
        if ((err = mp_add(&t1, &t2, &t1)) != MP_OKAY) {
           goto LBL_ERR1;
        }
        if ((err = mp_div_2(&t1, &t1)) != MP_OKAY) {
           goto LBL_ERR1;
        }
        /* t1 >= sqrt(arg) >= t2 at this point */
     } while (mp_cmp_mag(&t1, &t2) == MP_GT);
  
     mp_exch(&t1, ret);
  
  LBL_ERR1:
     mp_clear(&t2);
  LBL_ERR2:
     mp_clear(&t1);
     return err;
  }
  
  #endif
  

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