1#include <tommath.h>
2#ifdef BN_MP_KARATSUBA_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/* Karatsuba squaring, computes b = a*a using three
19 * half size squarings
20 *
21 * See comments of karatsuba_mul for details.  It
22 * is essentially the same algorithm but merely
23 * tuned to perform recursive squarings.
24 */
25int mp_karatsuba_sqr (mp_int * a, mp_int * b)
26{
27  mp_int  x0, x1, t1, t2, x0x0, x1x1;
28  int     B, err;
29
30  err = MP_MEM;
31
32  /* min # of digits */
33  B = a->used;
34
35  /* now divide in two */
36  B = B >> 1;
37
38  /* init copy all the temps */
39  if (mp_init_size (&x0, B) != MP_OKAY)
40    goto ERR;
41  if (mp_init_size (&x1, a->used - B) != MP_OKAY)
42    goto X0;
43
44  /* init temps */
45  if (mp_init_size (&t1, a->used * 2) != MP_OKAY)
46    goto X1;
47  if (mp_init_size (&t2, a->used * 2) != MP_OKAY)
48    goto T1;
49  if (mp_init_size (&x0x0, B * 2) != MP_OKAY)
50    goto T2;
51  if (mp_init_size (&x1x1, (a->used - B) * 2) != MP_OKAY)
52    goto X0X0;
53
54  {
55    register int x;
56    register mp_digit *dst, *src;
57
58    src = a->dp;
59
60    /* now shift the digits */
61    dst = x0.dp;
62    for (x = 0; x < B; x++) {
63      *dst++ = *src++;
64    }
65
66    dst = x1.dp;
67    for (x = B; x < a->used; x++) {
68      *dst++ = *src++;
69    }
70  }
71
72  x0.used = B;
73  x1.used = a->used - B;
74
75  mp_clamp (&x0);
76
77  /* now calc the products x0*x0 and x1*x1 */
78  if (mp_sqr (&x0, &x0x0) != MP_OKAY)
79    goto X1X1;           /* x0x0 = x0*x0 */
80  if (mp_sqr (&x1, &x1x1) != MP_OKAY)
81    goto X1X1;           /* x1x1 = x1*x1 */
82
83  /* now calc (x1+x0)**2 */
84  if (s_mp_add (&x1, &x0, &t1) != MP_OKAY)
85    goto X1X1;           /* t1 = x1 - x0 */
86  if (mp_sqr (&t1, &t1) != MP_OKAY)
87    goto X1X1;           /* t1 = (x1 - x0) * (x1 - x0) */
88
89  /* add x0y0 */
90  if (s_mp_add (&x0x0, &x1x1, &t2) != MP_OKAY)
91    goto X1X1;           /* t2 = x0x0 + x1x1 */
92  if (s_mp_sub (&t1, &t2, &t1) != MP_OKAY)
93    goto X1X1;           /* t1 = (x1+x0)**2 - (x0x0 + x1x1) */
94
95  /* shift by B */
96  if (mp_lshd (&t1, B) != MP_OKAY)
97    goto X1X1;           /* t1 = (x0x0 + x1x1 - (x1-x0)*(x1-x0))<<B */
98  if (mp_lshd (&x1x1, B * 2) != MP_OKAY)
99    goto X1X1;           /* x1x1 = x1x1 << 2*B */
100
101  if (mp_add (&x0x0, &t1, &t1) != MP_OKAY)
102    goto X1X1;           /* t1 = x0x0 + t1 */
103  if (mp_add (&t1, &x1x1, b) != MP_OKAY)
104    goto X1X1;           /* t1 = x0x0 + t1 + x1x1 */
105
106  err = MP_OKAY;
107
108X1X1:mp_clear (&x1x1);
109X0X0:mp_clear (&x0x0);
110T2:mp_clear (&t2);
111T1:mp_clear (&t1);
112X1:mp_clear (&x1);
113X0:mp_clear (&x0);
114ERR:
115  return err;
116}
117#endif
118
119/* $Source: /cvs/libtom/libtommath/bn_mp_karatsuba_sqr.c,v $ */
120/* $Revision: 1.6 $ */
121/* $Date: 2006/12/28 01:25:13 $ */
122