49 lines
1.8 KiB
Go
49 lines
1.8 KiB
Go
/*
|
|
Serene --- Yet an other Lisp
|
|
|
|
Copyright (c) 2020 Sameer Rahmani <lxsameer@gnu.org>
|
|
|
|
This program is free software; you can redistribute it and/or modify
|
|
it under the terms of the GNU General Public License as published by
|
|
the Free Software Foundation, either version 2 of the License.
|
|
|
|
This program is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
GNU General Public License for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
along with this program. If not, see <http://www.gnu.org/licenses/>.
|
|
*/
|
|
|
|
// Package hash provides the hashing functionality
|
|
package hash
|
|
|
|
import "hash/crc32"
|
|
|
|
var hashTable *crc32.Table = crc32.MakeTable(crc32.Castagnoli)
|
|
|
|
// IHashable is the interface types which allows expressions to have a hash
|
|
// value that doesn't change through out their life time. The origin
|
|
// of each expression can be checked by comparing their hashes. Basically
|
|
// two expressions with the same hash consider to be the same.
|
|
type IHashable interface {
|
|
// Returns a 32 bit hash of the the entity which implements it.
|
|
// The hash should be constant to the life time of the implementor.
|
|
Hash() uint32
|
|
}
|
|
|
|
func Of(in []byte) uint32 {
|
|
return crc32.Checksum(in, hashTable)
|
|
}
|
|
|
|
// CombineHashes combines two hashes and return a new one
|
|
func CombineHashes(hash1, hash2 uint32) uint32 {
|
|
// This way of composing hashes is used in libboost and almost everyone
|
|
// is using it. The 0x9e3779b9 is the integral part of the Golden Ratio's
|
|
// fractional part 0.61803398875… (sqrt(5)-1)/2, multiplied by 2^32.
|
|
// For more info: https://lkml.org/lkml/2016/4/29/838
|
|
hash1 ^= hash2 + 0x9e3779b9 + (hash1 << 6) + (hash2 >> 2)
|
|
return hash1
|
|
}
|