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

   1 #include <tommath.h>
   2 #ifdef BN_S_MP_SQR_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 /* low level squaring, b = a*a, HAC pp.596-597, Algorithm 14.16 */
  19 int s_mp_sqr (mp_int * a, mp_int * b)
  20 {
  21   mp_int  t;
  22   int     res, ix, iy, pa;
  23   mp_word r;
  24   mp_digit u, tmpx, *tmpt;
  25
  26   pa = a->used;
  27   if ((res = mp_init_size (&t, 2*pa + 1)) != MP_OKAY) {
  28     return res;
  29   }
  30
  31   /* default used is maximum possible size */
  32   t.used = 2*pa + 1;
  33
  34   for (ix = 0; ix < pa; ix++) {
  35     /* first calculate the digit at 2*ix */
  36     /* calculate double precision result */
  37     r = ((mp_word) t.dp[2*ix]) +
  38         ((mp_word)a->dp[ix])*((mp_word)a->dp[ix]);
  39
  40     /* store lower part in result */
  41     t.dp[ix+ix] = (mp_digit) (r & ((mp_word) MP_MASK));
  42
  43     /* get the carry */
  44     u           = (mp_digit)(r >> ((mp_word) DIGIT_BIT));
  45
  46     /* left hand side of A[ix] * A[iy] */
  47     tmpx        = a->dp[ix];
  48
  49     /* alias for where to store the results */
  50     tmpt        = t.dp + (2*ix + 1);
  51
  52     for (iy = ix + 1; iy < pa; iy++) {
  53       /* first calculate the product */
  54       r       = ((mp_word)tmpx) * ((mp_word)a->dp[iy]);
  55
  56       /* now calculate the double precision result, note we use
  57        * addition instead of *2 since it's easier to optimize
  58        */
  59       r       = ((mp_word) *tmpt) + r + r + ((mp_word) u);
  60
  61       /* store lower part */
  62       *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));
  63
  64       /* get carry */
  65       u       = (mp_digit)(r >> ((mp_word) DIGIT_BIT));
  66     }
  67     /* propagate upwards */
  68     while (u != ((mp_digit) 0)) {
  69       r       = ((mp_word) *tmpt) + ((mp_word) u);
  70       *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));
  71       u       = (mp_digit)(r >> ((mp_word) DIGIT_BIT));
  72     }
  73   }
  74
  75   mp_clamp (&t);
  76   mp_exch (&t, b);
  77   mp_clear (&t);
  78   return MP_OKAY;
  79 }
  80 #endif
  81
  82 /* $Source: /cvs/libtom/libtommath/bn_s_mp_sqr.c,v $ */
  83 /* $Revision: 1.3 $ */
  84 /* $Date: 2006/03/31 14:18:44 $ */