conterm/libmp/mpvecsub.c

35 lines
523 B
C

#include "os.h"
#include <mp.h>
#include "dat.h"
// prereq: a >= b, alen >= blen, diff has at least alen digits
void
mpvecsub(mpdigit *a, int alen, mpdigit *b, int blen, mpdigit *diff)
{
int i, borrow;
mpdigit x, y;
borrow = 0;
for(i = 0; i < blen; i++){
x = *a++;
y = *b++;
y += borrow;
if(y < borrow)
borrow = 1;
else
borrow = 0;
if(x < y)
borrow++;
*diff++ = x - y;
}
for(; i < alen; i++){
x = *a++;
y = x - borrow;
if(y > x)
borrow = 1;
else
borrow = 0;
*diff++ = y;
}
}