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://math.libtomcrypt.com
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 */
mp_karatsuba_sqr(mp_int * a,mp_int * b)25 int 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
108 X1X1:mp_clear (&x1x1);
109 X0X0:mp_clear (&x0x0);
110 T2:mp_clear (&t2);
111 T1:mp_clear (&t1);
112 X1:mp_clear (&x1);
113 X0:mp_clear (&x0);
114 ERR:
115 return err;
116 }
117 #endif
118
119 /* $Source: /cvs/libtom/libtommath/bn_mp_karatsuba_sqr.c,v $ */
120 /* $Revision: 1.5 $ */
121 /* $Date: 2006/03/31 14:18:44 $ */
122