Line data Source code
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 : */
25 2280 : 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 2280 : err = MP_MEM;
31 :
32 : /* min # of digits */
33 2280 : B = a->used;
34 :
35 : /* now divide in two */
36 2280 : B = B >> 1;
37 :
38 : /* init copy all the temps */
39 2280 : if (mp_init_size (&x0, B) != MP_OKAY)
40 0 : goto ERR;
41 2280 : if (mp_init_size (&x1, a->used - B) != MP_OKAY)
42 0 : goto X0;
43 :
44 : /* init temps */
45 2280 : if (mp_init_size (&t1, a->used * 2) != MP_OKAY)
46 0 : goto X1;
47 2280 : if (mp_init_size (&t2, a->used * 2) != MP_OKAY)
48 0 : goto T1;
49 2280 : if (mp_init_size (&x0x0, B * 2) != MP_OKAY)
50 0 : goto T2;
51 2280 : if (mp_init_size (&x1x1, (a->used - B) * 2) != MP_OKAY)
52 0 : goto X0X0;
53 :
54 : {
55 : register int x;
56 : register mp_digit *dst, *src;
57 :
58 2280 : src = a->dp;
59 :
60 : /* now shift the digits */
61 2280 : dst = x0.dp;
62 157320 : for (x = 0; x < B; x++) {
63 155040 : *dst++ = *src++;
64 : }
65 :
66 2280 : dst = x1.dp;
67 159600 : for (x = B; x < a->used; x++) {
68 157320 : *dst++ = *src++;
69 : }
70 : }
71 :
72 2280 : x0.used = B;
73 2280 : x1.used = a->used - B;
74 :
75 2280 : mp_clamp (&x0);
76 :
77 : /* now calc the products x0*x0 and x1*x1 */
78 2280 : if (mp_sqr (&x0, &x0x0) != MP_OKAY)
79 0 : goto X1X1; /* x0x0 = x0*x0 */
80 2280 : if (mp_sqr (&x1, &x1x1) != MP_OKAY)
81 0 : goto X1X1; /* x1x1 = x1*x1 */
82 :
83 : /* now calc (x1+x0)**2 */
84 2280 : if (s_mp_add (&x1, &x0, &t1) != MP_OKAY)
85 0 : goto X1X1; /* t1 = x1 - x0 */
86 2280 : if (mp_sqr (&t1, &t1) != MP_OKAY)
87 0 : goto X1X1; /* t1 = (x1 - x0) * (x1 - x0) */
88 :
89 : /* add x0y0 */
90 2280 : if (s_mp_add (&x0x0, &x1x1, &t2) != MP_OKAY)
91 0 : goto X1X1; /* t2 = x0x0 + x1x1 */
92 2280 : if (s_mp_sub (&t1, &t2, &t1) != MP_OKAY)
93 0 : goto X1X1; /* t1 = (x1+x0)**2 - (x0x0 + x1x1) */
94 :
95 : /* shift by B */
96 2280 : if (mp_lshd (&t1, B) != MP_OKAY)
97 0 : goto X1X1; /* t1 = (x0x0 + x1x1 - (x1-x0)*(x1-x0))<<B */
98 2280 : if (mp_lshd (&x1x1, B * 2) != MP_OKAY)
99 0 : goto X1X1; /* x1x1 = x1x1 << 2*B */
100 :
101 2280 : if (mp_add (&x0x0, &t1, &t1) != MP_OKAY)
102 0 : goto X1X1; /* t1 = x0x0 + t1 */
103 2280 : if (mp_add (&t1, &x1x1, b) != MP_OKAY)
104 0 : goto X1X1; /* t1 = x0x0 + t1 + x1x1 */
105 :
106 2280 : err = MP_OKAY;
107 :
108 2280 : X1X1:mp_clear (&x1x1);
109 2280 : X0X0:mp_clear (&x0x0);
110 2280 : T2:mp_clear (&t2);
111 2280 : T1:mp_clear (&t1);
112 2280 : X1:mp_clear (&x1);
113 2280 : X0:mp_clear (&x0);
114 2280 : ERR:
115 2280 : 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 $ */
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