kc3-lang/libtommath/mp_xor.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_xor.c

• #include "tommath_private.h"
  #ifdef MP_XOR_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  /* two complement xor */
  mp_err mp_xor(const mp_int *a, const mp_int *b, mp_int *c)
  {
     int used = MP_MAX(a->used, b->used) + 1, i;
     mp_err err;
     mp_digit ac = 1, bc = 1, cc = 1;
     bool neg = (a->sign != b->sign);
  
     if ((err = mp_grow(c, used)) != MP_OKAY) {
        return err;
     }
  
     for (i = 0; i < used; i++) {
        mp_digit x, y;
  
        /* convert to two complement if negative */
        if (mp_isneg(a)) {
           ac += (i >= a->used) ? MP_MASK : (~a->dp[i] & MP_MASK);
           x = ac & MP_MASK;
           ac >>= MP_DIGIT_BIT;
        } else {
           x = (i >= a->used) ? 0uL : a->dp[i];
        }
  
        /* convert to two complement if negative */
        if (mp_isneg(b)) {
           bc += (i >= b->used) ? MP_MASK : (~b->dp[i] & MP_MASK);
           y = bc & MP_MASK;
           bc >>= MP_DIGIT_BIT;
        } else {
           y = (i >= b->used) ? 0uL : b->dp[i];
        }
  
        c->dp[i] = x ^ y;
  
        /* convert to to sign-magnitude if negative */
        if (neg) {
           cc += ~c->dp[i] & MP_MASK;
           c->dp[i] = cc & MP_MASK;
           cc >>= MP_DIGIT_BIT;
        }
     }
  
     c->used = used;
     c->sign = (neg ? MP_NEG : MP_ZPOS);
     mp_clamp(c);
     return MP_OKAY;
  }
  #endif
  

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