3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality.
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.
12 * The library is free for all purposes without any express
15 * Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
18 /* reduces x mod m, assumes 0 < x < m**2, mu is
19 * precomputed via mp_reduce_setup.
20 * From HAC pp.604 Algorithm 14.42
22 int mp_reduce (mp_int * x, mp_int * m, mp_int * mu)
25 int res, um = m->used;
28 if ((res = mp_init_copy (&q, x)) != MP_OKAY) {
32 /* q1 = x / b**(k-1) */
35 /* according to HAC this optimization is ok */
36 if (((unsigned long) um) > (((mp_digit)1) << (DIGIT_BIT - 1))) {
37 if ((res = mp_mul (&q, mu, &q)) != MP_OKAY) {
41 #ifdef BN_S_MP_MUL_HIGH_DIGS_C
42 if ((res = s_mp_mul_high_digs (&q, mu, &q, um)) != MP_OKAY) {
45 #elif defined(BN_FAST_S_MP_MUL_HIGH_DIGS_C)
46 if ((res = fast_s_mp_mul_high_digs (&q, mu, &q, um)) != MP_OKAY) {
57 /* q3 = q2 / b**(k+1) */
60 /* x = x mod b**(k+1), quick (no division) */
61 if ((res = mp_mod_2d (x, DIGIT_BIT * (um + 1), x)) != MP_OKAY) {
65 /* q = q * m mod b**(k+1), quick (no division) */
66 if ((res = s_mp_mul_digs (&q, m, &q, um + 1)) != MP_OKAY) {
71 if ((res = mp_sub (x, &q, x)) != MP_OKAY) {
75 /* If x < 0, add b**(k+1) to it */
76 if (mp_cmp_d (x, 0) == MP_LT) {
78 if ((res = mp_lshd (&q, um + 1)) != MP_OKAY)
80 if ((res = mp_add (x, &q, x)) != MP_OKAY)
84 /* Back off if it's too big */
85 while (mp_cmp (x, m) != MP_LT) {
86 if ((res = s_mp_sub (x, m, x)) != MP_OKAY) {