release/src/router/dropbear/libtommath/bn_mp_dr_is_modulus.c

   1 #include <tommath.h>
   2 #ifdef BN_MP_DR_IS_MODULUS_C
   3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
   4  *
   5  * LibTomMath is a library that provides multiple-precision
   6  * integer arithmetic as well as number theoretic functionality.
   7  *
   8  * The library was designed directly after the MPI library by
   9  * Michael Fromberger but has been written from scratch with
  10  * additional optimizations in place.
  11  *
  12  * The library is free for all purposes without any express
  13  * guarantee it works.
  14  *
  15  * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com
  16  */
  17
  18 /* determines if a number is a valid DR modulus */
  19 int mp_dr_is_modulus(mp_int *a)
  20 {
  21    int ix;
  22
  23    /* must be at least two digits */
  24    if (a->used < 2) {
  25       return 0;
  26    }
  27
  28    /* must be of the form b**k - a [a <= b] so all
  29     * but the first digit must be equal to -1 (mod b).
  30     */
  31    for (ix = 1; ix < a->used; ix++) {
  32        if (a->dp[ix] != MP_MASK) {
  33           return 0;
  34        }
  35    }
  36    return 1;
  37 }
  38
  39 #endif
  40
  41 /* $Source: /cvs/libtom/libtommath/bn_mp_dr_is_modulus.c,v $ */
  42 /* $Revision: 1.3 $ */
  43 /* $Date: 2006/03/31 14:18:44 $ */