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

See also:

• md5 module for MD5 checksum algorithm
• base64 module for a base64 encoder and decoder
• std/sha1 module for a sha1 encoder and decoder
• tables module for hash tables

Imports

since

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 hashWangYi1(x: int64 | uint64 | Hash): Hash {...}{.inline.}

Wang Yi's hash_v1 for 8B int. https://github.com/rurban/smhasher has more details. This passed all scrambling tests in Spring 2019 and is simple. NOTE: It's ok to define proc(x: int16): Hash = hashWangYi1(Hash(x)). 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 hashIdentity[T: Ordinal | enum](x: T): Hash {...}{.inline.}

The identity hash. I.e. hashIdentity(x) = x. Source Edit

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

Efficient hashing of integers. Source Edit

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

Efficient hashing of floats. Source Edit

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

Efficient hashing of strings.

See also:

• hashIgnoreStyle
• hashIgnoreCase

Example:

doAssert hash("abracadabra") != hash("AbracadabrA")

Source Edit

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

Efficient hashing of null-terminated strings.

Example:

doAssert hash(cstring"abracadabra") == hash("abracadabra")
doAssert hash(cstring"AbracadabrA") == hash("AbracadabrA")
doAssert hash(cstring"abracadabra") != hash(cstring"AbracadabrA")

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 (included).

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

Example:

var a = "abracadabra"
doAssert hash(a, 0, 3) == hash(a, 7, 10)

Source Edit

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

Efficient hashing of strings; style is ignored.

Note: This uses different hashing algorithm than hash(string).

See also:

• hashIgnoreCase

Example:

doAssert hashIgnoreStyle("aBr_aCa_dAB_ra") == hashIgnoreStyle("abracadabra")
doAssert hashIgnoreStyle("abcdefghi") != hash("abcdefghi")

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 (included); style is ignored.

Note: This uses different hashing algorithm than hash(string).

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

Example:

var a = "ABracada_b_r_a"
doAssert hashIgnoreStyle(a, 0, 3) == hashIgnoreStyle(a, 7, a.high)

Source Edit

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

Efficient hashing of strings; case is ignored.

Note: This uses different hashing algorithm than hash(string).

See also:

• hashIgnoreStyle

Example:

doAssert hashIgnoreCase("ABRAcaDABRA") == hashIgnoreCase("abRACAdabra")
doAssert hashIgnoreCase("abcdefghi") != hash("abcdefghi")

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 (included); case is ignored.

Note: This uses different hashing algorithm than hash(string).

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

Example:

var a = "ABracadabRA"
doAssert hashIgnoreCase(a, 0, 3) == hashIgnoreCase(a, 7, 10)

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, from starting position sPos to ending position ePos (included).

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

Example:

let a = [1, 2, 5, 1, 2, 6]
doAssert hash(a, 0, 1) == hash(a, 3, 4)

Source Edit

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

Efficient hashing of sets. Source Edit