62 lines
1.4 KiB
C
62 lines
1.4 KiB
C
|
#include "tommath_private.h"
|
||
|
|
#ifdef MP_DIV_2D_C
|
||
|
|
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
|
||
|
|
/* SPDX-License-Identifier: Unlicense */
|
||
|
|
|
||
|
|
/* shift right by a certain bit count (store quotient in c, optional remainder in d) */
|
||
|
|
mp_err mp_div_2d(const mp_int *a, int b, mp_int *c, mp_int *d)
|
||
|
|
{
|
||
|
|
mp_err err;
|
||
|
|
|
||
|
|
if (b < 0) {
|
||
|
|
return MP_VAL;
|
||
|
|
}
|
||
|
|
|
||
|
|
if ((err = mp_copy(a, c)) != MP_OKAY) {
|
||
|
|
return err;
|
||
|
|
}
|
||
|
|
|
||
|
|
/* 'a' should not be used after here - it might be the same as d */
|
||
|
|
|
||
|
|
/* get the remainder */
|
||
|
|
if (d != NULL) {
|
||
|
|
if ((err = mp_mod_2d(a, b, d)) != MP_OKAY) {
|
||
|
|
return err;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
/* shift by as many digits in the bit count */
|
||
|
|
if (b >= MP_DIGIT_BIT) {
|
||
|
|
mp_rshd(c, b / MP_DIGIT_BIT);
|
||
|
|
}
|
||
|
|
|
||
|
|
/* shift any bit count < MP_DIGIT_BIT */
|
||
|
|
b %= MP_DIGIT_BIT;
|
||
|
|
if (b != 0u) {
|
||
|
|
int x;
|
||
|
|
mp_digit r, mask, shift;
|
||
|
|
|
||
|
|
/* mask */
|
||
|
|
mask = ((mp_digit)1 << b) - 1uL;
|
||
|
|
|
||
|
|
/* shift for lsb */
|
||
|
|
shift = (mp_digit)(MP_DIGIT_BIT - b);
|
||
|
|
|
||
|
|
/* carry */
|
||
|
|
r = 0;
|
||
|
|
for (x = c->used; x --> 0;) {
|
||
|
|
/* get the lower bits of this word in a temp */
|
||
|
|
mp_digit rr = c->dp[x] & mask;
|
||
|
|
|
||
|
|
/* shift the current word and mix in the carry bits from the previous word */
|
||
|
|
c->dp[x] = (c->dp[x] >> b) | (r << shift);
|
||
|
|
|
||
|
|
/* set the carry to the carry bits of the current word found above */
|
||
|
|
r = rr;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
mp_clamp(c);
|
||
|
|
return MP_OKAY;
|
||
|
|
}
|
||
|
|
#endif
|