1 #include "os.h"
2 #include <mp.h>
3 #include "dat.h"
4 
5 /* prereq: a >= b, alen >= blen, diff has at least alen digits */
6 void
7 mpvecsub(mpdigit *a, int alen, mpdigit *b, int blen, mpdigit *diff)
8 {
9 	int i, borrow;
10 	mpdigit x, y;
11 
12 	borrow = 0;
13 	for(i = 0; i < blen; i++){
14 		x = *a++;
15 		y = *b++;
16 		y += borrow;
17 		if(y < borrow)
18 			borrow = 1;
19 		else
20 			borrow = 0;
21 		if(x < y)
22 			borrow++;
23 		*diff++ = x - y;
24 	}
25 	for(; i < alen; i++){
26 		x = *a++;
27 		y = x - borrow;
28 		if(y > x)
29 			borrow = 1;
30 		else
31 			borrow = 0;
32 		*diff++ = y;
33 	}
34 }