package codex

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package codex
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Module HashingSource

Common tools to write custom hash-functions for our various types: Use hash2, hash3, hash4 or hash5 to create the hash of a tuple, hash_list to create the hash of a list and hash_sum to create the hash of a sum type.

For example, one might write a hash function for the given type as follows

    type t =
        | A
        | B of int
        | C of char * int
        | D of int list
        | E of { x: int; mutable y : int }
               (* mutable values should NOT be included in hash *)

    let hash x =
        let total = 5 in (* 5 total constructors *)
        match x with
        | A       -> hash_sum ~total ~nb:0 0 (* hash for constant is 0 *)
        | B i     -> hash_sum ~total ~nb:1 i
        | C(c,i)  -> hash_sum ~total ~nb:2 @@ hash2 (int_of_char c) i
        | D l     -> hash_sum ~total ~nb:3 @@ hash_list Fun.id l
        | E {x;_} -> hash_sum ~total ~nb:4 x
Sourceval hash_fast : 'a -> int

Fast hash function (for recursive subcalls), lots of collisions, only examines constructor tag

Sourceval hash_sum : nb:int -> total:int -> int -> int

hash_sum ~nb ~total value is used to generate a unique hash for sum types.

  • parameter nb

    is the constructor number (starting at 0)

  • parameter total

    is the total number of constructors nb < total

  • parameter value

    is the hash value of the constructors arguments

Sourceval hash2 : int -> int -> int

hash of a pair

Sourceval hash3 : int -> int -> int -> int

hash of a triplet

Sourceval hash4 : int -> int -> int -> int -> int

hash of a quadruplet

Sourceval hash5 : int -> int -> int -> int -> int -> int

hash of a quintuplet

Sourceval hash_list : ('a -> int) -> 'a list -> int

hash a list, using the given function to hash its elements