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
mpvecsub(mpdigit * a,int alen,mpdigit * b,int blen,mpdigit * diff)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 }
35