/* Add two values in F255. Partial reduction is performed (down to less than twice the modulus).  */
static void f255_add(uint32_t *d, const uint32_t *a, const uint32_t *b)
/* Add two values in F255. Partial reduction is performed (down to less than twice the modulus).  */
static void f255_add(uint32_t *d, const uint32_t *a, const uint32_t *b)
{
	int i;
	uint32_t cc, w;
	cc = 0;
	for (i = 0; i < 20; i ++) {
		w = a[i] + b[i] + cc;
		d[i] = w & 0x1FFF;
		cc = w >> 13;
	}
	cc = MUL15(w >> 8, 19);
	d[19] &= 0xFF;
	for (i = 0; i < 20; i ++) {
		w = d[i] + cc;
		d[i] = w & 0x1FFF;
		cc = w >> 13;
	}
}