7a68f12873
* git blame <renamed-file> is not affected * git log --follow <renamed-file> can be used to show log across renames
64 lines
1.4 KiB
C
64 lines
1.4 KiB
C
#include "tommath_private.h"
|
|
#ifdef MP_DIV_3_C
|
|
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
|
|
/* SPDX-License-Identifier: Unlicense */
|
|
|
|
/* divide by three (based on routine from MPI and the GMP manual) */
|
|
mp_err mp_div_3(const mp_int *a, mp_int *c, mp_digit *d)
|
|
{
|
|
mp_int q;
|
|
mp_word w, t;
|
|
mp_digit b;
|
|
mp_err err;
|
|
int ix;
|
|
|
|
/* b = 2**MP_DIGIT_BIT / 3 */
|
|
b = ((mp_word)1 << (mp_word)MP_DIGIT_BIT) / (mp_word)3;
|
|
|
|
if ((err = mp_init_size(&q, a->used)) != MP_OKAY) {
|
|
return err;
|
|
}
|
|
|
|
q.used = a->used;
|
|
q.sign = a->sign;
|
|
w = 0;
|
|
for (ix = a->used - 1; ix >= 0; ix--) {
|
|
w = (w << (mp_word)MP_DIGIT_BIT) | (mp_word)a->dp[ix];
|
|
|
|
if (w >= 3u) {
|
|
/* multiply w by [1/3] */
|
|
t = (w * (mp_word)b) >> (mp_word)MP_DIGIT_BIT;
|
|
|
|
/* now subtract 3 * [w/3] from w, to get the remainder */
|
|
w -= t+t+t;
|
|
|
|
/* fixup the remainder as required since
|
|
* the optimization is not exact.
|
|
*/
|
|
while (w >= 3u) {
|
|
t += 1u;
|
|
w -= 3u;
|
|
}
|
|
} else {
|
|
t = 0;
|
|
}
|
|
q.dp[ix] = (mp_digit)t;
|
|
}
|
|
|
|
/* [optional] store the remainder */
|
|
if (d != NULL) {
|
|
*d = (mp_digit)w;
|
|
}
|
|
|
|
/* [optional] store the quotient */
|
|
if (c != NULL) {
|
|
mp_clamp(&q);
|
|
mp_exch(&q, c);
|
|
}
|
|
mp_clear(&q);
|
|
|
|
return err;
|
|
}
|
|
|
|
#endif
|