Line data    Source code

       1             : #include "tommath_private.h"
       2             : #ifdef BN_MP_ADD_D_C
       3             : /* LibTomMath, multiple-precision integer library -- Tom St Denis */
       4             : /* SPDX-License-Identifier: Unlicense */
       5             : 
       6             : /* single digit addition */
       7           0 : mp_err mp_add_d(const mp_int *a, mp_digit b, mp_int *c)
       8             : {
       9           0 :    mp_err     err;
      10           0 :    int ix, oldused;
      11           0 :    mp_digit *tmpa, *tmpc;
      12             : 
      13             :    /* grow c as required */
      14           0 :    if (c->alloc < (a->used + 1)) {
      15           0 :       if ((err = mp_grow(c, a->used + 1)) != MP_OKAY) {
      16           0 :          return err;
      17             :       }
      18             :    }
      19             : 
      20             :    /* if a is negative and |a| >= b, call c = |a| - b */
      21           0 :    if ((a->sign == MP_NEG) && ((a->used > 1) || (a->dp[0] >= b))) {
      22           0 :       mp_int a_ = *a;
      23             :       /* temporarily fix sign of a */
      24           0 :       a_.sign = MP_ZPOS;
      25             : 
      26             :       /* c = |a| - b */
      27           0 :       err = mp_sub_d(&a_, b, c);
      28             : 
      29             :       /* fix sign  */
      30           0 :       c->sign = MP_NEG;
      31             : 
      32             :       /* clamp */
      33           0 :       mp_clamp(c);
      34             : 
      35           0 :       return err;
      36             :    }
      37             : 
      38             :    /* old number of used digits in c */
      39           0 :    oldused = c->used;
      40             : 
      41             :    /* source alias */
      42           0 :    tmpa    = a->dp;
      43             : 
      44             :    /* destination alias */
      45           0 :    tmpc    = c->dp;
      46             : 
      47             :    /* if a is positive */
      48           0 :    if (a->sign == MP_ZPOS) {
      49             :       /* add digits, mu is carry */
      50           0 :       mp_digit mu = b;
      51           0 :       for (ix = 0; ix < a->used; ix++) {
      52           0 :          *tmpc   = *tmpa++ + mu;
      53           0 :          mu      = *tmpc >> MP_DIGIT_BIT;
      54           0 :          *tmpc++ &= MP_MASK;
      55             :       }
      56             :       /* set final carry */
      57           0 :       ix++;
      58           0 :       *tmpc++  = mu;
      59             : 
      60             :       /* setup size */
      61           0 :       c->used = a->used + 1;
      62             :    } else {
      63             :       /* a was negative and |a| < b */
      64           0 :       c->used  = 1;
      65             : 
      66             :       /* the result is a single digit */
      67           0 :       if (a->used == 1) {
      68           0 :          *tmpc++  =  b - a->dp[0];
      69             :       } else {
      70           0 :          *tmpc++  =  b;
      71             :       }
      72             : 
      73             :       /* setup count so the clearing of oldused
      74             :        * can fall through correctly
      75             :        */
      76           0 :       ix       = 1;
      77             :    }
      78             : 
      79             :    /* sign always positive */
      80           0 :    c->sign = MP_ZPOS;
      81             : 
      82             :    /* now zero to oldused */
      83           0 :    MP_ZERO_DIGITS(tmpc, oldused - ix);
      84           0 :    mp_clamp(c);
      85             : 
      86           0 :    return MP_OKAY;
      87             : }
      88             : 
      89             : #endif