113 lines
2.2 KiB
C
113 lines
2.2 KiB
C
#include "tommath_private.h"
|
|
#ifdef BN_MP_DIV_D_C
|
|
/* LibTomMath, multiple-precision integer library -- Tom St Denis
|
|
*
|
|
* LibTomMath is a library that provides multiple-precision
|
|
* integer arithmetic as well as number theoretic functionality.
|
|
*
|
|
* The library was designed directly after the MPI library by
|
|
* Michael Fromberger but has been written from scratch with
|
|
* additional optimizations in place.
|
|
*
|
|
* SPDX-License-Identifier: Unlicense
|
|
*/
|
|
|
|
static int s_is_power_of_two(mp_digit b, int *p)
|
|
{
|
|
int x;
|
|
|
|
/* fast return if no power of two */
|
|
if ((b == 0u) || ((b & (b-1u)) != 0u)) {
|
|
return 0;
|
|
}
|
|
|
|
for (x = 0; x < DIGIT_BIT; x++) {
|
|
if (b == ((mp_digit)1<<(mp_digit)x)) {
|
|
*p = x;
|
|
return 1;
|
|
}
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/* single digit division (based on routine from MPI) */
|
|
int mp_div_d(const mp_int *a, mp_digit b, mp_int *c, mp_digit *d)
|
|
{
|
|
mp_int q;
|
|
mp_word w;
|
|
mp_digit t;
|
|
int res, ix;
|
|
|
|
/* cannot divide by zero */
|
|
if (b == 0u) {
|
|
return MP_VAL;
|
|
}
|
|
|
|
/* quick outs */
|
|
if ((b == 1u) || IS_ZERO(a)) {
|
|
if (d != NULL) {
|
|
*d = 0;
|
|
}
|
|
if (c != NULL) {
|
|
return mp_copy(a, c);
|
|
}
|
|
return MP_OKAY;
|
|
}
|
|
|
|
/* power of two ? */
|
|
if (s_is_power_of_two(b, &ix) == 1) {
|
|
if (d != NULL) {
|
|
*d = a->dp[0] & (((mp_digit)1<<(mp_digit)ix) - 1uL);
|
|
}
|
|
if (c != NULL) {
|
|
return mp_div_2d(a, ix, c, NULL);
|
|
}
|
|
return MP_OKAY;
|
|
}
|
|
|
|
#ifdef BN_MP_DIV_3_C
|
|
/* three? */
|
|
if (b == 3u) {
|
|
return mp_div_3(a, c, d);
|
|
}
|
|
#endif
|
|
|
|
/* no easy answer [c'est la vie]. Just division */
|
|
if ((res = mp_init_size(&q, a->used)) != MP_OKAY) {
|
|
return res;
|
|
}
|
|
|
|
q.used = a->used;
|
|
q.sign = a->sign;
|
|
w = 0;
|
|
for (ix = a->used - 1; ix >= 0; ix--) {
|
|
w = (w << (mp_word)DIGIT_BIT) | (mp_word)a->dp[ix];
|
|
|
|
if (w >= b) {
|
|
t = (mp_digit)(w / b);
|
|
w -= (mp_word)t * (mp_word)b;
|
|
} else {
|
|
t = 0;
|
|
}
|
|
q.dp[ix] = t;
|
|
}
|
|
|
|
if (d != NULL) {
|
|
*d = (mp_digit)w;
|
|
}
|
|
|
|
if (c != NULL) {
|
|
mp_clamp(&q);
|
|
mp_exch(&q, c);
|
|
}
|
|
mp_clear(&q);
|
|
|
|
return res;
|
|
}
|
|
|
|
#endif
|
|
|
|
/* ref: $Format:%D$ */
|
|
/* git commit: $Format:%H$ */
|
|
/* commit time: $Format:%ai$ */
|