// 1. lookup and build output word at the same time const uint32_t dword = lookup32[0][input[i + 0]] | lookup32[0][input[i + 1]]

// 1. lookup and build output word at the same time const uint32_t dword = lookup32[0][input[i + 0]] | lookup32[0][input[i + 1]] | lookup32[0][input[i + 2]] | lookup32[0][input[i + 3]]; // 2. save 32 bits reinterpret_cast<uint32_t*>(out) = dword; out += 3; Do you mean lookup32[0]... | lookup32[1] ... | ..[2] | [3], instead?