#include "tommath_private.h"

#ifdef BN_S_MP_SQR_C

/* LibTomMath, multiple-precision integer library -- Tom St Denis */

/* SPDX-License-Identifier: Unlicense */

/* low level squaring, b = a*a, HAC pp.596-597, Algorithm 14.16 */

mp_err s_mp_sqr(const mp_int *a, mp_int *b)

{

   mp_int   t;

   int      ix, iy, pa;

   mp_err   err;

   mp_word  r;

   mp_digit u, tmpx, *tmpt;

   pa = a->used;

   if ((err = mp_init_size(&t, (2 * pa) + 1)) != MP_OKAY) {

      return err;

   }

   /* default used is maximum possible size */

   t.used = (2 * pa) + 1;

   for (ix = 0; ix < pa; ix++) {

      /* first calculate the digit at 2*ix */

      /* calculate double precision result */

      r = (mp_word)t.dp[2*ix] +

          ((mp_word)a->dp[ix] * (mp_word)a->dp[ix]);

      /* store lower part in result */

      t.dp[ix+ix] = (mp_digit)(r & (mp_word)MP_MASK);

      /* get the carry */

      u           = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);

      /* left hand side of A[ix] * A[iy] */

      tmpx        = a->dp[ix];

      /* alias for where to store the results */

      tmpt        = t.dp + ((2 * ix) + 1);

      for (iy = ix + 1; iy < pa; iy++) {

         /* first calculate the product */

         r       = (mp_word)tmpx * (mp_word)a->dp[iy];

         /* now calculate the double precision result, note we use

          * addition instead of *2 since it's easier to optimize

          */

         r       = (mp_word)*tmpt + r + r + (mp_word)u;

         /* store lower part */

         *tmpt++ = (mp_digit)(r & (mp_word)MP_MASK);

         /* get carry */

         u       = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);

      }

      /* propagate upwards */

      while (u != 0uL) {

         r       = (mp_word)*tmpt + (mp_word)u;

         *tmpt++ = (mp_digit)(r & (mp_word)MP_MASK);

         u       = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);

      }

   }

   mp_clamp(&t);

   mp_exch(&t, b);

   mp_clear(&t);

   return MP_OKAY;

}

#endif