1
// Copyright 2019+ Klaus Post. All rights reserved.
2
// License information can be found in the LICENSE file.
3
// Based on work by Yann Collet, released under BSD License.
8
prime3bytes = 506832829
9
prime4bytes = 2654435761
10
prime5bytes = 889523592379
11
prime6bytes = 227718039650203
12
prime7bytes = 58295818150454627
13
prime8bytes = 0xcf1bbcdcb7a56463
16
// hashLen returns a hash of the lowest mls bytes of with length output bits.
17
// mls must be >=3 and <=8. Any other value will return hash for 4 bytes.
18
// length should always be < 32.
19
// Preferably length and mls should be a constant for inlining.
20
func hashLen(u uint64, length, mls uint8) uint32 {
23
return (uint32(u<<8) * prime3bytes) >> (32 - length)
25
return uint32(((u << (64 - 40)) * prime5bytes) >> (64 - length))
27
return uint32(((u << (64 - 48)) * prime6bytes) >> (64 - length))
29
return uint32(((u << (64 - 56)) * prime7bytes) >> (64 - length))
31
return uint32((u * prime8bytes) >> (64 - length))
33
return (uint32(u) * prime4bytes) >> (32 - length)
37
// hash3 returns the hash of the lower 3 bytes of u to fit in a hash table with h bits.
38
// Preferably h should be a constant and should always be <32.
39
func hash3(u uint32, h uint8) uint32 {
40
return ((u << (32 - 24)) * prime3bytes) >> ((32 - h) & 31)