### view libtommath/bn_mp_mul_2d.c @ 1734:73646de50f13DROPBEAR_2020.80

version 2020.80
author Matt Johnston Fri, 26 Jun 2020 21:45:59 +0800 1051e4eea25a
line wrap: on
line source
```#include "tommath_private.h"
#ifdef BN_MP_MUL_2D_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */

/* 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;

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
```