kc3-lang/libtommath/s_mp_sqr.c

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• Hash : 143e0376
  Author :
  Date : 2019-10-29T20:02:32
  

  simplifications: basic arithmetic functions

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• s_mp_sqr.c

• #include "tommath_private.h"
  #ifdef 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, pa;
     mp_err   err;
  
     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++) {
        mp_digit u;
        int iy;
  
        /* first calculate the digit at 2*ix */
        /* calculate double precision result */
        mp_word 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);
  
        for (iy = ix + 1; iy < pa; iy++) {
           /* first calculate the product */
           r       = (mp_word)a->dp[ix] * (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)t.dp[ix + iy] + r + r + (mp_word)u;
  
           /* store lower part */
           t.dp[ix + iy] = (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)t.dp[ix + iy] + (mp_word)u;
           t.dp[ix + iy] = (mp_digit)(r & (mp_word)MP_MASK);
           u       = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);
           ++iy;
        }
     }
  
     mp_clamp(&t);
     mp_exch(&t, b);
     mp_clear(&t);
     return MP_OKAY;
  }
  #endif
  

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