/* number of output digits to produce */
pa = MIN(digs, a->used + b->used);
+ if (!pa)
+ return MP_VAL;
/* clear the carry */
_W = 0;
/* number of output digits to produce */
pa = a->used + b->used;
+ if (!pa)
+ return MP_VAL;
+
_W = 0;
for (ix = digs; ix < pa; ix++) {
int tx, ty, iy;