//
//   input to be strictly less than the prime modulus (m), and also
//
//   require the input to be in the unique saturated representation.
//
//   All functions also ensure that these two properties are true of
//
//   return values.
//
//
//
// Computed values:
//
//   eval z = z[0] + (z[1] << 64) + (z[2] << 128) + (z[3] << 192) + (z[4] << 256) + (z[5] << 0x140)
//