1 #include "tommath_private.h"
2 #ifdef BN_MP_DIV_D_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
4 /* SPDX-License-Identifier: Unlicense */
5
6 /* single digit division (based on routine from MPI) */
mp_div_d(const mp_int * a,mp_digit b,mp_int * c,mp_digit * d)7 mp_err mp_div_d(const mp_int *a, mp_digit b, mp_int *c, mp_digit *d)
8 {
9 mp_int q;
10 mp_word w;
11 mp_digit t;
12 mp_err err;
13 int ix;
14
15 /* cannot divide by zero */
16 if (b == 0u) {
17 return MP_VAL;
18 }
19
20 /* quick outs */
21 if ((b == 1u) || MP_IS_ZERO(a)) {
22 if (d != NULL) {
23 *d = 0;
24 }
25 if (c != NULL) {
26 return mp_copy(a, c);
27 }
28 return MP_OKAY;
29 }
30
31 /* power of two ? */
32 if ((b & (b - 1u)) == 0u) {
33 ix = 1;
34 while ((ix < MP_DIGIT_BIT) && (b != (((mp_digit)1)<<ix))) {
35 ix++;
36 }
37 if (d != NULL) {
38 *d = a->dp[0] & (((mp_digit)1<<(mp_digit)ix) - 1uL);
39 }
40 if (c != NULL) {
41 return mp_div_2d(a, ix, c, NULL);
42 }
43 return MP_OKAY;
44 }
45
46 /* three? */
47 if (MP_HAS(MP_DIV_3) && (b == 3u)) {
48 return mp_div_3(a, c, d);
49 }
50
51 /* no easy answer [c'est la vie]. Just division */
52 if ((err = mp_init_size(&q, a->used)) != MP_OKAY) {
53 return err;
54 }
55
56 q.used = a->used;
57 q.sign = a->sign;
58 w = 0;
59 for (ix = a->used - 1; ix >= 0; ix--) {
60 w = (w << (mp_word)MP_DIGIT_BIT) | (mp_word)a->dp[ix];
61
62 if (w >= b) {
63 t = (mp_digit)(w / b);
64 w -= (mp_word)t * (mp_word)b;
65 } else {
66 t = 0;
67 }
68 q.dp[ix] = t;
69 }
70
71 if (d != NULL) {
72 *d = (mp_digit)w;
73 }
74
75 if (c != NULL) {
76 mp_clamp(&q);
77 mp_exch(&q, c);
78 }
79 mp_clear(&q);
80
81 return err;
82 }
83
84 #endif
85