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#include "tommath_private.h"
#ifdef BN_MP_MUL_2D_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
/* shift left by a certain bit count */
mp_err mp_mul_2d(const mp_int *a, int b, mp_int *c)
{
mp_digit d;
mp_err err;
/* copy */
if (a != c) {
if ((err = mp_copy(a, c)) != MP_OKAY) {
return err;
}
}
if (c->alloc < (c->used + (b / MP_DIGIT_BIT) + 1)) {
if ((err = mp_grow(c, c->used + (b / MP_DIGIT_BIT) + 1)) != MP_OKAY) {
return err;
}
}
/* shift by as many digits in the bit count */
if (b >= MP_DIGIT_BIT) {
if ((err = mp_lshd(c, b / MP_DIGIT_BIT)) != MP_OKAY) {
return err;
}
}
/* shift any bit count < MP_DIGIT_BIT */
d = (mp_digit)(b % MP_DIGIT_BIT);
if (d != 0u) {
mp_digit *tmpc, shift, mask, r, rr;
int x;
/* bitmask for carries */
mask = ((mp_digit)1 << d) - (mp_digit)1;
/* shift for msbs */
shift = (mp_digit)MP_DIGIT_BIT - d;
/* alias */
tmpc = c->dp;
/* carry */
r = 0;
for (x = 0; x < c->used; x++) {
/* get the higher bits of the current word */
rr = (*tmpc >> shift) & mask;
/* shift the current word and OR in the carry */
*tmpc = ((*tmpc << d) | r) & MP_MASK;
++tmpc;
/* set the carry to the carry bits of the current word */
r = rr;
}
/* set final carry */
if (r != 0u) {
c->dp[(c->used)++] = r;
}
}
mp_clamp(c);
return MP_OKAY;
}
#endif
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