pub const D0: d128 = d128{ bytes: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 34] };
pub const D1: d128 = d128{ bytes: [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 34] };
pub const D2: d128 = d128{ bytes: [2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 34] };
pub const DP5: d128 = d128{ bytes: [5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 192, 7, 34] };
pub const D90: d128 = d128{ bytes: [26, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 34] };
pub const D180: d128 = d128{ bytes: [138, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 34] };
pub const D200: d128 = d128{ bytes: [0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 34] };
/// e
pub const DE: d128 = d128{ bytes: [98, 75, 23, 231, 90, 224, 213, 84, 68, 150, 46, 45, 132, 249, 255, 41] };
/// π
pub const DPI: d128 = d128{ bytes: [131, 230, 181, 218, 208, 98, 226, 180, 251, 179, 83, 235, 26, 204, 255, 45] };
/// π/2
pub const DPI2: d128 = d128{ bytes: [209, 231, 188, 113, 104, 49, 101, 236, 177, 246, 166, 233, 15, 239, 255, 37] };
/// φ
pub const DGOLDEN_RATIO: d128 = d128{ bytes: [56, 151, 199, 163, 186, 4, 185, 232, 97, 242, 238, 204, 128, 241, 255, 37] };
/// ∞
pub const DINFINITY: d128 = d128{ bytes: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 120] };
/// -∞
pub const DNEG_INFINITY: d128 = d128{ bytes: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 248] };
However, I propose adding a d128::from_bytes function. It would take the raw bytes in as little endian, and convert to the system endianness.