package maphash

Import Path
	hash/maphash (on go.dev)

Dependency Relation
	imports one package, and imported by 0 packages


Involved Source Files

	
		Package maphash provides hash functions on byte sequences.
		These hash functions are intended to be used to implement hash tables or
		other data structures that need to map arbitrary strings or byte
		sequences to a uniform distribution on unsigned 64-bit integers.
		Each different instance of a hash table or data structure should use its own [Seed].
		
		The hash functions are not cryptographically secure.
		(See crypto/sha256 and crypto/sha512 for cryptographic use.)

	    maphash_runtime.go


Code Examples

	
		package main
		
		import (
			"fmt"
			"hash/maphash"
		)
		
		func main() {
			// The zero Hash value is valid and ready to use; setting an
			// initial seed is not necessary.
			var h maphash.Hash
		
			// Add a string to the hash, and print the current hash value.
			h.WriteString("hello, ")
			fmt.Printf("%#x\n", h.Sum64())
		
			// Append additional data (in the form of a byte array).
			h.Write([]byte{'w', 'o', 'r', 'l', 'd'})
			fmt.Printf("%#x\n", h.Sum64())
		
			// Reset discards all data previously added to the Hash, without
			// changing its seed.
			h.Reset()
		
			// Use SetSeed to create a new Hash h2 which will behave
			// identically to h.
			var h2 maphash.Hash
			h2.SetSeed(h.Seed())
		
			h.WriteString("same")
			h2.WriteString("same")
			fmt.Printf("%#x == %#x\n", h.Sum64(), h2.Sum64())
		}




Package-Level Type Names (total 2)


	/* sort by:  |  */
	
		A Hash computes a seeded hash of a byte sequence.
		
		The zero Hash is a valid Hash ready to use.
		A zero Hash chooses a random seed for itself during
		the first call to a Reset, Write, Seed, or Sum64 method.
		For control over the seed, use SetSeed.
		
		The computed hash values depend only on the initial seed and
		the sequence of bytes provided to the Hash object, not on the way
		in which the bytes are provided. For example, the three sequences
		
			h.Write([]byte{'f','o','o'})
			h.WriteByte('f'); h.WriteByte('o'); h.WriteByte('o')
			h.WriteString("foo")
		
		all have the same effect.
		
		Hashes are intended to be collision-resistant, even for situations
		where an adversary controls the byte sequences being hashed.
		
		A Hash is not safe for concurrent use by multiple goroutines, but a Seed is.
		If multiple goroutines must compute the same seeded hash,
		each can declare its own Hash and call SetSeed with a common Seed.

		
			
				BlockSize returns h's block size.

			
				Reset discards all bytes added to h.
				(The seed remains the same.)

			
				Seed returns h's seed value.

			
				SetSeed sets h to use seed, which must have been returned by [MakeSeed]
				or by another [Hash.Seed] method.
				Two [Hash] objects with the same seed behave identically.
				Two [Hash] objects with different seeds will very likely behave differently.
				Any bytes added to h before this call will be discarded.

			
				Size returns h's hash value size, 8 bytes.

			
				Sum appends the hash's current 64-bit value to b.
				It exists for implementing [hash.Hash].
				For direct calls, it is more efficient to use [Hash.Sum64].

			
				Sum64 returns h's current 64-bit value, which depends on
				h's seed and the sequence of bytes added to h since the
				last call to [Hash.Reset] or [Hash.SetSeed].
				
				All bits of the Sum64 result are close to uniformly and
				independently distributed, so it can be safely reduced
				by using bit masking, shifting, or modular arithmetic.

			
				Write adds b to the sequence of bytes hashed by h.
				It always writes all of b and never fails; the count and error result are for implementing [io.Writer].

			
				WriteByte adds b to the sequence of bytes hashed by h.
				It never fails; the error result is for implementing [io.ByteWriter].

			
				WriteString adds the bytes of s to the sequence of bytes hashed by h.
				It always writes all of s and never fails; the count and error result are for implementing [io.StringWriter].

		
			*Hash : hash.Hash
			*Hash : hash.Hash64
			*Hash : internal/bisect.Writer
			*Hash : io.ByteWriter
			*Hash : io.StringWriter
			*Hash : io.Writer


	
		A Seed is a random value that selects the specific hash function
		computed by a [Hash]. If two Hashes use the same Seeds, they
		will compute the same hash values for any given input.
		If two Hashes use different Seeds, they are very likely to compute
		distinct hash values for any given input.
		
		A Seed must be initialized by calling [MakeSeed].
		The zero seed is uninitialized and not valid for use with [Hash]'s SetSeed method.
		
		Each Seed value is local to a single process and cannot be serialized
		or otherwise recreated in a different process.

		
			func MakeSeed() Seed
			func (*Hash).Seed() Seed
		
			func Bytes(seed Seed, b []byte) uint64
			func String(seed Seed, s string) uint64
			func (*Hash).SetSeed(seed Seed)




Package-Level Functions (total 3)


	
		Bytes returns the hash of b with the given seed.
		
		Bytes is equivalent to, but more convenient and efficient than:
		
			var h Hash
			h.SetSeed(seed)
			h.Write(b)
			return h.Sum64()


	
		MakeSeed returns a new random seed.


	
		String returns the hash of s with the given seed.
		
		String is equivalent to, but more convenient and efficient than:
		
			var h Hash
			h.SetSeed(seed)
			h.WriteString(s)
			return h.Sum64()