Mercurial > dropbear

comparison libtommath/bn_mp_karatsuba_sqr.c @ 284:eed26cff980b

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583) to branch 'au.asn.ucc.matt.dropbear' (head fff0894a0399405a9410ea1c6d118f342cf2aa64)
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:23:49 +0000
parents
children 5ff8218bcee9
comparison
equal deleted inserted replaced
283:bd240aa12ba7 284:eed26cff980b
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, [email protected], http://math.libtomcrypt.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 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 (mp_sub (&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 (mp_sub (&t2, &t1, &t1) != MP_OKAY)
93 goto X1X1; /* t1 = x0x0 + x1x1 - (x1-x0)*(x1-x0) */
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