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Annotation of researchv10no/cmd/sml/src/util/strghash.sml, revision 1.1.1.1

1.1       root        1: (* Copyright 1989 by AT&T Bell Laboratories *)
                      2: (* util/strghash.sml *)
                      3: 
                      4: structure StrgHash =
                      5: struct
                      6: 
                      7:   val prime = 8388593 (* largest prime less than 2^23 *)
                      8:   val base = 128
                      9: 
                     10: (* the simple version --
                     11:     fun hashString(str: string) : int =
                     12:         let fun loop (0,n) = n
                     13:              | loop (i,n) = 
                     14:                  let val i = i-1
                     15:                      val n' = (base * n + ordof(str,i)) 
                     16:                   in loop (i, (n' - prime * (n' div prime)))
                     17:                  end
                     18:         in loop (size str,0)
                     19:        end
                     20: *)
                     21: 
                     22:   fun hashString(str: string) : int =
                     23:       let val l = size str
                     24:        in case l
                     25:            of 0 => 0
                     26:             | 1 => ord str
                     27:             | 2 => ordof(str,0) + base * ordof(str,1)
                     28:             | 3 => ordof(str,0) + base * (ordof(str,1) + base * ordof(str,2))
                     29:             | _ =>
                     30:                let fun loop (0,n) = n
                     31:                      | loop (i,n) = 
                     32:                          let val i = i-1
                     33:                              val n' = (base * n + ordof(str,i)) 
                     34:                           in loop (i, (n' - prime * (n' div prime)))
                     35:                          end
                     36:                 in loop (l,0)
                     37:                end
                     38:       end
                     39: 
                     40: end (* structure StrgHash *)
                     41: 
                     42: 
                     43: 

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