Module hashes

This module implements efficient computations of hash values for diverse Nim types. All the procs are based on these two building blocks:

• !& proc used to start or mix a hash value, and
• !$ proc used to finish the hash value.

If you want to implement hash procs for your custom types you will end up writing the following kind of skeleton of code:

proc hash(x: Something): Hash =
  ## Computes a Hash from `x`.
  var h: Hash = 0
  # Iterate over parts of `x`.
  for xAtom in x:
    # Mix the atom with the partial hash.
    h = h !& xAtom
  # Finish the hash.
  result = !$h

If your custom types contain fields for which there already is a hash proc, like for example objects made up of strings, you can simply hash together the hash value of the individual fields:

proc hash(x: Something): Hash =
  ## Computes a Hash from `x`.
  var h: Hash = 0
  h = h !& hash(x.foo)
  h = h !& hash(x.bar)
  result = !$h

Imports

strutils

Types

Hash = int

a hash value; hash tables using these values should always have a size of a power of two and can use the and operator instead of mod for truncation of the hash value.

Procs

proc `!&`(h: Hash; val: int): Hash {.inline, raises: [], tags: [].}

mixes a hash value h with val to produce a new hash value. This is only needed if you need to implement a hash proc for a new datatype.

proc `!$`(h: Hash): Hash {.inline, raises: [], tags: [].}

finishes the computation of the hash value. This is only needed if you need to implement a hash proc for a new datatype.

proc hashData(data: pointer; size: int): Hash {.raises: [], tags: [].}

hashes an array of bytes of size size

proc hash(x: pointer): Hash {.inline, raises: [], tags: [].}

efficient hashing of pointers

proc hash[T: proc](x: T): Hash {.inline.}

efficient hashing of proc vars; closures are supported too.

proc hash(x: int): Hash {.inline, raises: [], tags: [].}

efficient hashing of integers

proc hash(x: int64): Hash {.inline, raises: [], tags: [].}

efficient hashing of int64 integers

proc hash(x: uint): Hash {.inline, raises: [], tags: [].}

efficient hashing of unsigned integers

proc hash(x: uint64): Hash {.inline, raises: [], tags: [].}

efficient hashing of uint64 integers

proc hash(x: char): Hash {.inline, raises: [], tags: [].}

efficient hashing of characters

proc hash[T: Ordinal](x: T): Hash {.inline.}

efficient hashing of other ordinal types (e.g., enums)

proc hash(x: string): Hash {.raises: [], tags: [].}

efficient hashing of strings

proc hash(x: cstring): Hash {.raises: [], tags: [].}

efficient hashing of null-terminated strings

proc hash(sBuf: string; sPos, ePos: int): Hash {.raises: [], tags: [].}

efficient hashing of a string buffer, from starting position sPos to ending position ePos

hash(myStr, 0, myStr.high) is equivalent to hash(myStr)

proc hashIgnoreStyle(x: string): Hash {.raises: [], tags: [].}

efficient hashing of strings; style is ignored

proc hashIgnoreStyle(sBuf: string; sPos, ePos: int): Hash {.raises: [], tags: [].}

efficient hashing of a string buffer, from starting position sPos to ending position ePos; style is ignored

hashIgnoreStyle(myBuf, 0, myBuf.high) is equivalent to hashIgnoreStyle(myBuf)

proc hashIgnoreCase(x: string): Hash {.raises: [], tags: [].}

efficient hashing of strings; case is ignored

proc hashIgnoreCase(sBuf: string; sPos, ePos: int): Hash {.raises: [], tags: [].}

efficient hashing of a string buffer, from starting position sPos to ending position ePos; case is ignored

hashIgnoreCase(myBuf, 0, myBuf.high) is equivalent to hashIgnoreCase(myBuf)

proc hash(x: float): Hash {.inline, raises: [], tags: [].}

efficient hashing of floats.

proc hash[T: tuple](x: T): Hash

efficient hashing of tuples.

proc hash[A](x: openArray[A]): Hash

efficient hashing of arrays and sequences.

proc hash[A](aBuf: openArray[A]; sPos, ePos: int): Hash

efficient hashing of portions of arrays and sequences.

hash(myBuf, 0, myBuf.high) is equivalent to hash(myBuf)

proc hash[A](x: set[A]): Hash

efficient hashing of sets.