84 lines
2.0 KiB
C
84 lines
2.0 KiB
C
#include "tommath_private.h"
|
|
#ifdef BN_MP_DIV_2D_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
|
|
*/
|
|
|
|
/* shift right by a certain bit count (store quotient in c, optional remainder in d) */
|
|
int mp_div_2d(const mp_int *a, int b, mp_int *c, mp_int *d)
|
|
{
|
|
mp_digit D, r, rr;
|
|
int x, res;
|
|
|
|
/* if the shift count is <= 0 then we do no work */
|
|
if (b <= 0) {
|
|
res = mp_copy(a, c);
|
|
if (d != NULL) {
|
|
mp_zero(d);
|
|
}
|
|
return res;
|
|
}
|
|
|
|
/* copy */
|
|
if ((res = mp_copy(a, c)) != MP_OKAY) {
|
|
return res;
|
|
}
|
|
/* 'a' should not be used after here - it might be the same as d */
|
|
|
|
/* get the remainder */
|
|
if (d != NULL) {
|
|
if ((res = mp_mod_2d(a, b, d)) != MP_OKAY) {
|
|
return res;
|
|
}
|
|
}
|
|
|
|
/* shift by as many digits in the bit count */
|
|
if (b >= DIGIT_BIT) {
|
|
mp_rshd(c, b / DIGIT_BIT);
|
|
}
|
|
|
|
/* shift any bit count < DIGIT_BIT */
|
|
D = (mp_digit)(b % DIGIT_BIT);
|
|
if (D != 0u) {
|
|
mp_digit *tmpc, mask, shift;
|
|
|
|
/* mask */
|
|
mask = ((mp_digit)1 << D) - 1uL;
|
|
|
|
/* shift for lsb */
|
|
shift = (mp_digit)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
|
|
|
|
/* ref: $Format:%D$ */
|
|
/* git commit: $Format:%H$ */
|
|
/* commit time: $Format:%ai$ */
|