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://libtom.org
16 */
17
18/* low level squaring, b = a*a, HAC pp.596-597, Algorithm 14.16 */
19int 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: 1.4 $ */
84/* $Date: 2006/12/28 01:25:13 $ */
85