text: /*	$NetBSD: bn_mp_div_d.c,v 1.1.1.2 2014/04/24 12:45:31 pettai Exp $	*/
  
  #include <tommath.h>
  #ifdef BN_MP_DIV_D_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis
   *
   * LibTomMath is a library that provides multiple-precision
   * integer arithmetic as well as number theoretic functionality.
   *
   * The library was designed directly after the MPI library by
   * Michael Fromberger but has been written from scratch with
   * additional optimizations in place.
   *
   * The library is free for all purposes without any express
   * guarantee it works.
   *
   * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
   */
  
  static int s_is_power_of_two(mp_digit b, int *p)
  {
     int x;
  
     /* fast return if no power of two */
     if ((b==0) || (b & (b-1))) {
        return 0;
     }
  
     for (x = 0; x < DIGIT_BIT; x++) {
        if (b == (((mp_digit)1)<<x)) {
           *p = x;
           return 1;
        }
     }
     return 0;
  }
  
  /* single digit division (based on routine from MPI) */
  int mp_div_d (mp_int * a, mp_digit b, mp_int * c, mp_digit * d)
  {
    mp_int  q;
    mp_word w;
    mp_digit t;
    int     res, ix;
  
    /* cannot divide by zero */
    if (b == 0) {
       return MP_VAL;
    }
  
    /* quick outs */
    if (b == 1 || mp_iszero(a) == 1) {
       if (d != NULL) {
          *d = 0;
       }
       if (c != NULL) {
          return mp_copy(a, c);
       }
       return MP_OKAY;
    }
  
    /* power of two ? */
    if (s_is_power_of_two(b, &ix) == 1) {
       if (d != NULL) {
          *d = a->dp[0] & ((((mp_digit)1)<<ix) - 1);
       }
       if (c != NULL) {
          return mp_div_2d(a, ix, c, NULL);
       }
       return MP_OKAY;
    }
  
  #ifdef BN_MP_DIV_3_C
    /* three? */
    if (b == 3) {
       return mp_div_3(a, c, d);
    }
  #endif
  
    /* no easy answer [c'est la vie].  Just division */
    if ((res = mp_init_size(&q, a->used)) != MP_OKAY) {
       return res;
    }
  
    q.used = a->used;
    q.sign = a->sign;
    w = 0;
    for (ix = a->used - 1; ix >= 0; ix--) {
       w = (w << ((mp_word)DIGIT_BIT)) | ((mp_word)a->dp[ix]);
  
       if (w >= b) {
          t = (mp_digit)(w / b);
          w -= ((mp_word)t) * ((mp_word)b);
        } else {
          t = 0;
        }
        q.dp[ix] = (mp_digit)t;
    }
  
    if (d != NULL) {
       *d = (mp_digit)w;
    }
  
    if (c != NULL) {
       mp_clamp(&q);
       mp_exch(&q, c);
    }
    mp_clear(&q);
  
    return res;
  }
  
  #endif
  
  /* Source: /cvs/libtom/libtommath/bn_mp_div_d.c,v  */
  /* Revision: 1.5  */
  /* Date: 2007/01/09 04:44:32  */
  