view libtommath/bn_s_mp_mul_high_digs_fast.c @ 1851:7f549ee3df48 default tip main master

Use HOME before /etc/passwd to find id_dropbear (#137) Currently dbclient uses the value of HOME by default when looking for ~/.ssh/known_hosts, falling back to /etc/passwd if HOME is not set (so that people can work around broken values in /etc/passwd). However, when locating the default authentication key (defaults to ~/.ssh/id_dropbear), paths not starting with / are always prefixed with the value from /etc/passwd. Make the behaviour consistent by adjusting expand_homedir_path to use the value of HOME, falling back to /etc/passwd if HOME is not set.
author Matt Robinson <git@nerdoftheherd.com>
date Tue, 19 Oct 2021 06:02:47 +0100
parents 1051e4eea25a
children
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#include "tommath_private.h"
#ifdef BN_S_MP_MUL_HIGH_DIGS_FAST_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */

/* this is a modified version of fast_s_mul_digs that only produces
 * output digits *above* digs.  See the comments for fast_s_mul_digs
 * to see how it works.
 *
 * This is used in the Barrett reduction since for one of the multiplications
 * only the higher digits were needed.  This essentially halves the work.
 *
 * Based on Algorithm 14.12 on pp.595 of HAC.
 */
mp_err s_mp_mul_high_digs_fast(const mp_int *a, const mp_int *b, mp_int *c, int digs)
{
   int     olduse, pa, ix, iz;
   mp_err   err;
   mp_digit W[MP_WARRAY];
   mp_word  _W;

   /* grow the destination as required */
   pa = a->used + b->used;
   if (c->alloc < pa) {
      if ((err = mp_grow(c, pa)) != MP_OKAY) {
         return err;
      }
   }

   /* number of output digits to produce */
   pa = a->used + b->used;
   _W = 0;
   for (ix = digs; ix < pa; ix++) {
      int      tx, ty, iy;
      mp_digit *tmpx, *tmpy;

      /* get offsets into the two bignums */
      ty = MP_MIN(b->used-1, ix);
      tx = ix - ty;

      /* setup temp aliases */
      tmpx = a->dp + tx;
      tmpy = b->dp + ty;

      /* this is the number of times the loop will iterrate, essentially its
         while (tx++ < a->used && ty-- >= 0) { ... }
       */
      iy = MP_MIN(a->used-tx, ty+1);

      /* execute loop */
      for (iz = 0; iz < iy; iz++) {
         _W += (mp_word)*tmpx++ * (mp_word)*tmpy--;
      }

      /* store term */
      W[ix] = (mp_digit)_W & MP_MASK;

      /* make next carry */
      _W = _W >> (mp_word)MP_DIGIT_BIT;
   }

   /* setup dest */
   olduse  = c->used;
   c->used = pa;

   {
      mp_digit *tmpc;

      tmpc = c->dp + digs;
      for (ix = digs; ix < pa; ix++) {
         /* now extract the previous digit [below the carry] */
         *tmpc++ = W[ix];
      }

      /* clear unused digits [that existed in the old copy of c] */
      MP_ZERO_DIGITS(tmpc, olduse - ix);
   }
   mp_clamp(c);
   return MP_OKAY;
}
#endif