Register Spill

// arr has 1M doubles
constexpr int N = 14;

double sums[N] = {1.0, ...};
for (auto i = 0u; i < arr.size(); i += N) {
  for (int j = 0; j < N; ++j)
    sums[j] = sums[j] * 1.01 + arr[i + j];
}

// arr.len == 1'000'000
const N = 4;

var i: usize = 0;
while (i < arr.len) : (i += N) {
    inline for (0..N) |j| {
        sum +%= arr[i + j] *% @intCast(i + j);
    }
}

// arr has 1M doubles
constexpr int N = 16;

double sums[N] = {1.0, ...};
for (auto i = 0u; i < arr.size(); i += N) {
  for (int j = 0; j < N; ++j)
    sums[j] = sums[j] * 1.01 + arr[i + j];
}

// arr.len == 1'000'000
const N = 8;

var i: usize = 0;
while (i < arr.len) : (i += N) {
    inline for (0..N) |j| {
        sum +%= arr[i + j] *% @intCast(i + j);
    }
}