kc3-lang/libtommath/s_mp_add.c

• Show log

  Commit

• Hash : bcda8fc6
  Author :
  Date : 2019-10-29T22:38:49
  

  simplifications: remove unnecessary optimization * these double checks are not necessary * the compiler will move the early return outside of the called function, basically the functions is partially inlined * however lto/amalgamation needed for the optimization

Download

• s_mp_add.c

• #include "tommath_private.h"
  #ifdef S_MP_ADD_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  /* low level addition, based on HAC pp.594, Algorithm 14.7 */
  mp_err s_mp_add(const mp_int *a, const mp_int *b, mp_int *c)
  {
     int oldused, min, max, i;
     mp_digit u;
     mp_err err;
  
     /* find sizes, we let |a| <= |b| which means we have to sort
      * them.  "x" will point to the input with the most digits
      */
     if (a->used < b->used) {
        MP_EXCH(const mp_int *, a, b);
     }
  
     min = b->used;
     max = a->used;
  
     /* init result */
     if ((err = mp_grow(c, max + 1)) != MP_OKAY) {
        return err;
     }
  
     /* get old used digit count and set new one */
     oldused = c->used;
     c->used = max + 1;
  
     /* zero the carry */
     u = 0;
     for (i = 0; i < min; i++) {
        /* Compute the sum at one digit, T[i] = A[i] + B[i] + U */
        c->dp[i] = a->dp[i] + b->dp[i] + u;
  
        /* U = carry bit of T[i] */
        u = c->dp[i] >> (mp_digit)MP_DIGIT_BIT;
  
        /* take away carry bit from T[i] */
        c->dp[i] &= MP_MASK;
     }
  
     /* now copy higher words if any, that is in A+B
      * if A or B has more digits add those in
      */
     if (min != max) {
        for (; i < max; i++) {
           /* T[i] = A[i] + U */
           c->dp[i] = a->dp[i] + u;
  
           /* U = carry bit of T[i] */
           u = c->dp[i] >> (mp_digit)MP_DIGIT_BIT;
  
           /* take away carry bit from T[i] */
           c->dp[i] &= MP_MASK;
        }
     }
  
     /* add carry */
     c->dp[i] = u;
  
     /* clear digits above oldused */
     s_mp_zero_digs(c->dp + c->used, oldused - c->used);
  
     mp_clamp(c);
     return MP_OKAY;
  }
  #endif
  

Download