Line data    Source code

       1             : #include <tommath.h>
       2             : #ifdef BN_MP_DIV_2D_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://libtom.org
      16             :  */
      17             : 
      18             : /* shift right by a certain bit count (store quotient in c, optional remainder in d) */
      19      260688 : int mp_div_2d (mp_int * a, int b, mp_int * c, mp_int * d)
      20             : {
      21             :   mp_digit D, r, rr;
      22             :   int     x, res;
      23             :   mp_int  t;
      24             : 
      25             : 
      26             :   /* if the shift count is <= 0 then we do no work */
      27      260688 :   if (b <= 0) {
      28           0 :     res = mp_copy (a, c);
      29           0 :     if (d != NULL) {
      30           0 :       mp_zero (d);
      31             :     }
      32           0 :     return res;
      33             :   }
      34             : 
      35      260688 :   if ((res = mp_init (&t)) != MP_OKAY) {
      36           0 :     return res;
      37             :   }
      38             : 
      39             :   /* get the remainder */
      40      260688 :   if (d != NULL) {
      41           0 :     if ((res = mp_mod_2d (a, b, &t)) != MP_OKAY) {
      42           0 :       mp_clear (&t);
      43           0 :       return res;
      44             :     }
      45             :   }
      46             : 
      47             :   /* copy */
      48      260688 :   if ((res = mp_copy (a, c)) != MP_OKAY) {
      49           0 :     mp_clear (&t);
      50           0 :     return res;
      51             :   }
      52             : 
      53             :   /* shift by as many digits in the bit count */
      54      260688 :   if (b >= (int)DIGIT_BIT) {
      55           0 :     mp_rshd (c, b / DIGIT_BIT);
      56             :   }
      57             : 
      58             :   /* shift any bit count < DIGIT_BIT */
      59      260688 :   D = (mp_digit) (b % DIGIT_BIT);
      60      260688 :   if (D != 0) {
      61             :     register mp_digit *tmpc, mask, shift;
      62             : 
      63             :     /* mask */
      64      260688 :     mask = (((mp_digit)1) << D) - 1;
      65             : 
      66             :     /* shift for lsb */
      67      260688 :     shift = DIGIT_BIT - D;
      68             : 
      69             :     /* alias */
      70      260688 :     tmpc = c->dp + (c->used - 1);
      71             : 
      72             :     /* carry */
      73      260688 :     r = 0;
      74    12422099 :     for (x = c->used - 1; x >= 0; x--) {
      75             :       /* get the lower  bits of this word in a temp */
      76    12161411 :       rr = *tmpc & mask;
      77             : 
      78             :       /* shift the current word and mix in the carry bits from the previous word */
      79    12161411 :       *tmpc = (*tmpc >> D) | (r << shift);
      80    12161411 :       --tmpc;
      81             : 
      82             :       /* set the carry to the carry bits of the current word found above */
      83    12161411 :       r = rr;
      84             :     }
      85             :   }
      86      260688 :   mp_clamp (c);
      87      260688 :   if (d != NULL) {
      88           0 :     mp_exch (&t, d);
      89             :   }
      90      260688 :   mp_clear (&t);
      91      260688 :   return MP_OKAY;
      92             : }
      93             : #endif
      94             : 
      95             : /* $Source: /cvs/libtom/libtommath/bn_mp_div_2d.c,v $ */
      96             : /* $Revision: 1.4 $ */
      97             : /* $Date: 2006/12/28 01:25:13 $ */