### view libtommath/bn_s_mp_mul_high_digs.c @ 1785:9026f976eee8

fuzz: work around fuzz_connect_remote() limitations
author Matt Johnston Sun, 06 Dec 2020 21:27:25 +0800 1051e4eea25a
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```#include "tommath_private.h"
#ifdef BN_S_MP_MUL_HIGH_DIGS_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */

/* multiplies |a| * |b| and does not compute the lower digs digits
* [meant to get the higher part of the product]
*/
mp_err s_mp_mul_high_digs(const mp_int *a, const mp_int *b, mp_int *c, int digs)
{
mp_int   t;
int      pa, pb, ix, iy;
mp_err   err;
mp_digit u;
mp_word  r;
mp_digit tmpx, *tmpt, *tmpy;

/* can we use the fast multiplier? */
if (MP_HAS(S_MP_MUL_HIGH_DIGS_FAST)
&& ((a->used + b->used + 1) < MP_WARRAY)
&& (MP_MIN(a->used, b->used) < MP_MAXFAST)) {
return s_mp_mul_high_digs_fast(a, b, c, digs);
}

if ((err = mp_init_size(&t, a->used + b->used + 1)) != MP_OKAY) {
return err;
}
t.used = a->used + b->used + 1;

pa = a->used;
pb = b->used;
for (ix = 0; ix < pa; ix++) {
/* clear the carry */
u = 0;

/* left hand side of A[ix] * B[iy] */
tmpx = a->dp[ix];

/* alias to the address of where the digits will be stored */
tmpt = &(t.dp[digs]);

/* alias for where to read the right hand side from */
tmpy = b->dp + (digs - ix);

for (iy = digs - ix; iy < pb; iy++) {
/* calculate the double precision result */
r       = (mp_word)*tmpt +
((mp_word)tmpx * (mp_word)*tmpy++) +
(mp_word)u;

/* get the lower part */