Line data    Source code

       1             : #include "tommath_private.h"
       2             : #ifdef BN_MP_DIV_2D_C
       3             : /* LibTomMath, multiple-precision integer library -- Tom St Denis */
       4             : /* SPDX-License-Identifier: Unlicense */
       5             : 
       6             : /* shift right by a certain bit count (store quotient in c, optional remainder in d) */
       7       49082 : mp_err mp_div_2d(const mp_int *a, int b, mp_int *c, mp_int *d)
       8             : {
       9             :    mp_digit D, r, rr;
      10             :    int     x;
      11             :    mp_err err;
      12             : 
      13             :    /* if the shift count is <= 0 then we do no work */
      14       49082 :    if (b <= 0) {
      15           0 :       err = mp_copy(a, c);
      16           0 :       if (d != NULL) {
      17           0 :          mp_zero(d);
      18             :       }
      19           0 :       return err;
      20             :    }
      21             : 
      22             :    /* copy */
      23       49082 :    if ((err = mp_copy(a, c)) != MP_OKAY) {
      24           0 :       return err;
      25             :    }
      26             :    /* 'a' should not be used after here - it might be the same as d */
      27             : 
      28             :    /* get the remainder */
      29       49082 :    if (d != NULL) {
      30           0 :       if ((err = mp_mod_2d(a, b, d)) != MP_OKAY) {
      31           0 :          return err;
      32             :       }
      33             :    }
      34             : 
      35             :    /* shift by as many digits in the bit count */
      36       49082 :    if (b >= MP_DIGIT_BIT) {
      37           0 :       mp_rshd(c, b / MP_DIGIT_BIT);
      38             :    }
      39             : 
      40             :    /* shift any bit count < MP_DIGIT_BIT */
      41       49082 :    D = (mp_digit)(b % MP_DIGIT_BIT);
      42       49082 :    if (D != 0u) {
      43             :       mp_digit *tmpc, mask, shift;
      44             : 
      45             :       /* mask */
      46       49082 :       mask = ((mp_digit)1 << D) - 1uL;
      47             : 
      48             :       /* shift for lsb */
      49       49082 :       shift = (mp_digit)MP_DIGIT_BIT - D;
      50             : 
      51             :       /* alias */
      52       49082 :       tmpc = c->dp + (c->used - 1);
      53             : 
      54             :       /* carry */
      55       49082 :       r = 0;
      56     1501357 :       for (x = c->used - 1; x >= 0; x--) {
      57             :          /* get the lower  bits of this word in a temp */
      58     1452275 :          rr = *tmpc & mask;
      59             : 
      60             :          /* shift the current word and mix in the carry bits from the previous word */
      61     1452275 :          *tmpc = (*tmpc >> D) | (r << shift);
      62     1452275 :          --tmpc;
      63             : 
      64             :          /* set the carry to the carry bits of the current word found above */
      65     1452275 :          r = rr;
      66             :       }
      67             :    }
      68       49082 :    mp_clamp(c);
      69       49082 :    return MP_OKAY;
      70             : }
      71             : #endif