|
282
|
1 #include <tommath.h> |
|
|
2 #ifdef BN_MP_DIV_D_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 static int s_is_power_of_two(mp_digit b, int *p) |
|
|
19 { |
|
|
20 int x; |
|
|
21 |
|
|
22 for (x = 1; x < DIGIT_BIT; x++) { |
|
|
23 if (b == (((mp_digit)1)<<x)) { |
|
|
24 *p = x; |
|
|
25 return 1; |
|
|
26 } |
|
|
27 } |
|
|
28 return 0; |
|
|
29 } |
|
|
30 |
|
|
31 /* single digit division (based on routine from MPI) */ |
|
|
32 int mp_div_d (mp_int * a, mp_digit b, mp_int * c, mp_digit * d) |
|
|
33 { |
|
|
34 mp_int q; |
|
|
35 mp_word w; |
|
|
36 mp_digit t; |
|
|
37 int res, ix; |
|
|
38 |
|
|
39 /* cannot divide by zero */ |
|
|
40 if (b == 0) { |
|
|
41 return MP_VAL; |
|
|
42 } |
|
|
43 |
|
|
44 /* quick outs */ |
|
|
45 if (b == 1 || mp_iszero(a) == 1) { |
|
|
46 if (d != NULL) { |
|
|
47 *d = 0; |
|
|
48 } |
|
|
49 if (c != NULL) { |
|
|
50 return mp_copy(a, c); |
|
|
51 } |
|
|
52 return MP_OKAY; |
|
|
53 } |
|
|
54 |
|
|
55 /* power of two ? */ |
|
|
56 if (s_is_power_of_two(b, &ix) == 1) { |
|
|
57 if (d != NULL) { |
|
|
58 *d = a->dp[0] & ((((mp_digit)1)<<ix) - 1); |
|
|
59 } |
|
|
60 if (c != NULL) { |
|
|
61 return mp_div_2d(a, ix, c, NULL); |
|
|
62 } |
|
|
63 return MP_OKAY; |
|
|
64 } |
|
|
65 |
|
|
66 #ifdef BN_MP_DIV_3_C |
|
|
67 /* three? */ |
|
|
68 if (b == 3) { |
|
|
69 return mp_div_3(a, c, d); |
|
|
70 } |
|
|
71 #endif |
|
|
72 |
|
|
73 /* no easy answer [c'est la vie]. Just division */ |
|
|
74 if ((res = mp_init_size(&q, a->used)) != MP_OKAY) { |
|
|
75 return res; |
|
|
76 } |
|
|
77 |
|
|
78 q.used = a->used; |
|
|
79 q.sign = a->sign; |
|
|
80 w = 0; |
|
|
81 for (ix = a->used - 1; ix >= 0; ix--) { |
|
|
82 w = (w << ((mp_word)DIGIT_BIT)) | ((mp_word)a->dp[ix]); |
|
|
83 |
|
|
84 if (w >= b) { |
|
|
85 t = (mp_digit)(w / b); |
|
|
86 w -= ((mp_word)t) * ((mp_word)b); |
|
|
87 } else { |
|
|
88 t = 0; |
|
|
89 } |
|
|
90 q.dp[ix] = (mp_digit)t; |
|
|
91 } |
|
|
92 |
|
|
93 if (d != NULL) { |
|
|
94 *d = (mp_digit)w; |
|
|
95 } |
|
|
96 |
|
|
97 if (c != NULL) { |
|
|
98 mp_clamp(&q); |
|
|
99 mp_exch(&q, c); |
|
|
100 } |
|
|
101 mp_clear(&q); |
|
|
102 |
|
|
103 return res; |
|
|
104 } |
|
|
105 |
|
|
106 #endif |
