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/* LibTomFloat, multiple-precision floating-point library
*
* LibTomFloat is a library that provides multiple-precision
* floating-point artihmetic as well as trigonometric functionality.
*
* This library requires the public domain LibTomMath to be installed.
*
* This library is free for all purposes without any express
* gurantee it works
*
* Tom St Denis, tomstdenis@iahu.ca, http://float.libtomcrypt.org
*/
#include <tomfloat.h>
/* compute using sqrt(x) = y_{n+1} = 0.5 * (y_{n} + x/y_{n}) */
int mpf_sqrt(mp_float *a, mp_float *b)
{
mp_float oldval, tmp, res;
int err, itts;
/* make sure it's positive */
if (a->mantissa.sign == MP_NEG) {
return MP_VAL;
}
/* let's roll */
if ((err = mpf_init_multi(b->radix, &oldval, &tmp, &res, NULL)) != MP_OKAY) {
return err;
}
/* get copy of a and make reasonable guestimte towards the sqrt */
if ((err = mpf_copy(a, &res)) != MP_OKAY) { goto __ERR; }
mp_rshd(&(res.mantissa), res.mantissa.used >> 1);
res.exp = res.exp / 2;
if ((err = mpf_normalize_to(&res, b->radix)) != MP_OKAY) { goto __ERR; }
/* number of iterations */
itts = mpf_iterations(b);
while (itts--) {
if ((err = mpf_copy(&res, &oldval)) != MP_OKAY) { goto __ERR; }
/* compute x/res */
if ((err = mpf_div(a, &res, &tmp)) != MP_OKAY) { goto __ERR; }
/* res + x/res */
if ((err = mpf_add(&res, &tmp, &res)) != MP_OKAY) { goto __ERR; }
/* 0.5 * (res + x/res) */
if ((err = mpf_div_2(&res, &res)) != MP_OKAY) { goto __ERR; }
if (mpf_cmp(&res, &oldval) == MP_EQ) {
break;
}
}
mpf_exch(&res, b);
__ERR: mpf_clear_multi(&oldval, &tmp, &res, NULL);
return err;
}
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