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#include "tommath_private.h"
#ifdef BN_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_digit D, r, rr;
int x;
mp_err err;
/* if the shift count is <= 0 then we do no work */
if (b <= 0) {
err = mp_copy(a, c);
if (d != NULL) {
mp_zero(d);
}
return err;
}
/* copy */
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 */
D = (mp_digit)(b % MP_DIGIT_BIT);
if (D != 0u) {
mp_digit *tmpc, mask, shift;
/* mask */
mask = ((mp_digit)1 << D) - 1uL;
/* shift for lsb */
shift = (mp_digit)MP_DIGIT_BIT - D;
/* alias */
tmpc = c->dp + (c->used - 1);
/* carry */
r = 0;
for (x = c->used - 1; x >= 0; x--) {
/* get the lower bits of this word in a temp */
rr = *tmpc & mask;
/* shift the current word and mix in the carry bits from the previous word */
*tmpc = (*tmpc >> D) | (r << shift);
--tmpc;
/* set the carry to the carry bits of the current word found above */
r = rr;
}
}
mp_clamp(c);
return MP_OKAY;
}
#endif
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