r = r (op) a.
The result is computed modulo r.len.
fn llaccum(comptime op: AccOp, r: []Limb, a: []const Limb) void
fn llaccum(comptime op: AccOp, r: []Limb, a: []const Limb) void {
assert(!slicesOverlap(r, a) or @intFromPtr(r.ptr) <= @intFromPtr(a.ptr));
if (op == .sub) {
_ = llsubcarry(r, r, a);
return;
}
assert(r.len != 0 and a.len != 0);
assert(r.len >= a.len);
var i: usize = 0;
var carry: Limb = 0;
while (i < a.len) : (i += 1) {
const ov1 = @addWithOverflow(r[i], a[i]);
r[i] = ov1[0];
const ov2 = @addWithOverflow(r[i], carry);
r[i] = ov2[0];
carry = @as(Limb, ov1[1]) + ov2[1];
}
while ((carry != 0) and i < r.len) : (i += 1) {
const ov = @addWithOverflow(r[i], carry);
r[i] = ov[0];
carry = ov[1];
}
}