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

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.   Source Edit

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.   Source Edit
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.   Source Edit
proc hashData(data: pointer; size: int): Hash {.
raises: [], tags: []
.}
hashes an array of bytes of size size   Source Edit
proc hash(x: pointer): Hash {.
inline, raises: [], tags: []
.}
efficient hashing of pointers   Source Edit
proc hash[T: proc](x: T): Hash {.
inline
.}
efficient hashing of proc vars; closures are supported too.   Source Edit
proc hash(x: int): Hash {.
inline, raises: [], tags: []
.}
efficient hashing of integers   Source Edit
proc hash(x: int64): Hash {.
inline, raises: [], tags: []
.}
efficient hashing of int64 integers   Source Edit
proc hash(x: uint): Hash {.
inline, raises: [], tags: []
.}
efficient hashing of unsigned integers   Source Edit
proc hash(x: uint64): Hash {.
inline, raises: [], tags: []
.}
efficient hashing of uint64 integers   Source Edit
proc hash(x: char): Hash {.
inline, raises: [], tags: []
.}
efficient hashing of characters   Source Edit
proc hash[T: Ordinal](x: T): Hash {.
inline
.}
efficient hashing of other ordinal types (e.g., enums)   Source Edit
proc hash(x: string): Hash {.
raises: [], tags: []
.}
efficient hashing of strings   Source Edit
proc hash(x: cstring): Hash {.
raises: [], tags: []
.}
efficient hashing of null-terminated strings   Source Edit
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)

  Source Edit
proc hashIgnoreStyle(x: string): Hash {.
raises: [], tags: []
.}
efficient hashing of strings; style is ignored   Source Edit
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)

  Source Edit
proc hashIgnoreCase(x: string): Hash {.
raises: [], tags: []
.}
efficient hashing of strings; case is ignored   Source Edit
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)

  Source Edit
proc hash(x: float): Hash {.
inline, raises: [], tags: []
.}
efficient hashing of floats.   Source Edit
proc hash[T: tuple](x: T): Hash
efficient hashing of tuples.   Source Edit
proc hash[A](x: openArray[A]): Hash
efficient hashing of arrays and sequences.   Source Edit
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)

  Source Edit
proc hash[A](x: set[A]): Hash
efficient hashing of sets.   Source Edit