Function ec_add

modules/crypt/arith/xsBigIntEx.c:725–832

 */

static void ec_add(txMachine *the, txECPoint *r, txECPoint *a, txECPoint *b, txECParam *ec, pool_t *pool)
{
    txBigInt *Z1Z1, *Z2Z2, *U1, *U2, *S1, *S2, *H, *I, *J, *R, *V, *X3, *Y3, *Z3;
    txBigInt *t1, *t2;
    txBigInt *m = ec->m;

	if (fxBigInt_iszero(a->z)) {
		fxBigInt_copy(r->x, b->x);
		fxBigInt_copy(r->y, b->y);
		fxBigInt_copy(r->z, b->z);
		return;
	}
	else if (fxBigInt_iszero(b->z)) {
		fxBigInt_copy(r->x, a->x);
		fxBigInt_copy(r->y, a->y);
		fxBigInt_copy(r->z, a->z);
		return;
	}
	
	t1 = pool_get(the, m->size, pool);
	t2 = pool_get(the, m->size, pool);
	Z1Z1 = pool_get(the, m->size, pool);
	Z2Z2 = pool_get(the, m->size, pool);
	U1 = pool_get(the, m->size, pool);
	U2 = pool_get(the, m->size, pool);
	S1 = pool_get(the, m->size, pool);
	S2 = pool_get(the, m->size, pool);

    Z1Z1 = fxBigInt_mont_square(the, Z1Z1, a->z, m, ec->u, pool);
    Z2Z2 = fxBigInt_mont_square(the, Z2Z2, b->z, m, ec->u, pool);
    U1 = fxBigInt_mont_mul(the, U1, a->x, Z2Z2, m, ec->u, pool);
    U2 = fxBigInt_mont_mul(the, U2, b->x, Z1Z1, m, ec->u, pool);
	t1 = fxBigInt_mont_mul(the, t1, a->y, b->z, m, ec->u, pool);
	S1 = fxBigInt_mont_mul(the, S1, t1, Z2Z2, m, ec->u, pool);
	t1 = fxBigInt_mont_mul(the, t1, b->y, a->z, m, ec->u, pool);
	S2 = fxBigInt_mont_mul(the, S2, t1, Z1Z1, m, ec->u, pool);

	if (fxBigInt_ucomp(U1, U2) == 0) {
		int eq = fxBigInt_ucomp(S1, S2) == 0;
		pool_put(S2, m->size);
		pool_put(S1, m->size);
		pool_put(U2, m->size);
		pool_put(U1, m->size);
		pool_put(Z2Z2, m->size);
		pool_put(Z1Z1, m->size);
		pool_put(t2, m->size);
		pool_put(t1, m->size);
		if (eq)
			ec_double(the, r, a, ec, pool);
		else {
			// zero?
			fxBigInt_copy(r->z, &gxBigIntZero);
		}
		return;
	}

	H = pool_get(the, m->size, pool);
	I = pool_get(the, m->size, pool);