Line data    Source code

       1             : #include "tommath_private.h"
       2             : #ifdef BN_MP_LSHD_C
       3             : /* LibTomMath, multiple-precision integer library -- Tom St Denis */
       4             : /* SPDX-License-Identifier: Unlicense */
       5             : 
       6             : /* shift left a certain amount of digits */
       7       17443 : mp_err mp_lshd(mp_int *a, int b)
       8             : {
       9             :    int x;
      10             :    mp_err err;
      11             :    mp_digit *top, *bottom;
      12             : 
      13             :    /* if its less than zero return */
      14       17443 :    if (b <= 0) {
      15         352 :       return MP_OKAY;
      16             :    }
      17             :    /* no need to shift 0 around */
      18       17091 :    if (MP_IS_ZERO(a)) {
      19           0 :       return MP_OKAY;
      20             :    }
      21             : 
      22             :    /* grow to fit the new digits */
      23       17091 :    if (a->alloc < (a->used + b)) {
      24         684 :       if ((err = mp_grow(a, a->used + b)) != MP_OKAY) {
      25           0 :          return err;
      26             :       }
      27             :    }
      28             : 
      29             :    /* increment the used by the shift amount then copy upwards */
      30       17091 :    a->used += b;
      31             : 
      32             :    /* top */
      33       17091 :    top = a->dp + a->used - 1;
      34             : 
      35             :    /* base */
      36       17091 :    bottom = (a->dp + a->used - 1) - b;
      37             : 
      38             :    /* much like mp_rshd this is implemented using a sliding window
      39             :     * except the window goes the otherway around.  Copying from
      40             :     * the bottom to the top.  see bn_mp_rshd.c for more info.
      41             :     */
      42      987321 :    for (x = a->used - 1; x >= b; x--) {
      43      970230 :       *top-- = *bottom--;
      44             :    }
      45             : 
      46             :    /* zero the lower digits */
      47       17091 :    MP_ZERO_DIGITS(a->dp, b);
      48             : 
      49       17091 :    return MP_OKAY;
      50             : }
      51             : #endif