code: func NewPermutationGenerator(m int64, seed int64) *PermutationGenerator {
  	// figure out 'a' and 'c', return PermutationGenerator
  	a := multiplierFromModulus(m, seed)
  	c := int64(22695479)
  	return &PermutationGenerator{a, c, m}
  }
docs: // NewPermutationGenerator returns a PermutationGenerator which will permute
  // numbers in 0-n.