kc3-lang/libtommath/mp_mul_2d.c

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

  simplifications: basic arithmetic functions

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• mp_mul_2d.c

• #include "tommath_private.h"
  #ifdef MP_MUL_2D_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  /* shift left by a certain bit count */
  mp_err mp_mul_2d(const mp_int *a, int b, mp_int *c)
  {
     if (b < 0) {
        return MP_VAL;
     }
  
     if (a != c) {
        mp_err err;
        if ((err = mp_copy(a, c)) != MP_OKAY) {
           return err;
        }
     }
  
     if (c->alloc < (c->used + (b / MP_DIGIT_BIT) + 1)) {
        mp_err err;
        if ((err = mp_grow(c, c->used + (b / MP_DIGIT_BIT) + 1)) != MP_OKAY) {
           return err;
        }
     }
  
     /* shift by as many digits in the bit count */
     if (b >= MP_DIGIT_BIT) {
        mp_err err;
        if ((err = mp_lshd(c, b / MP_DIGIT_BIT)) != MP_OKAY) {
           return err;
        }
     }
  
     /* shift any bit count < MP_DIGIT_BIT */
     b %= MP_DIGIT_BIT;
     if (b != 0u) {
        mp_digit shift, mask, r;
        int x;
  
        /* bitmask for carries */
        mask = ((mp_digit)1 << b) - (mp_digit)1;
  
        /* shift for msbs */
        shift = (mp_digit)(MP_DIGIT_BIT - b);
  
        /* carry */
        r    = 0;
        for (x = 0; x < c->used; x++) {
           /* get the higher bits of the current word */
           mp_digit rr = (c->dp[x] >> shift) & mask;
  
           /* shift the current word and OR in the carry */
           c->dp[x] = ((c->dp[x] << b) | r) & MP_MASK;
  
           /* set the carry to the carry bits of the current word */
           r = rr;
        }
  
        /* set final carry */
        if (r != 0u) {
           c->dp[(c->used)++] = r;
        }
     }
     mp_clamp(c);
     return MP_OKAY;
  }
  #endif
  

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