78 lines
2.6 KiB
Go
78 lines
2.6 KiB
Go
// Copyright 2019+ Klaus Post. All rights reserved.
|
|
// License information can be found in the LICENSE file.
|
|
// Based on work by Yann Collet, released under BSD License.
|
|
|
|
package zstd
|
|
|
|
const (
|
|
prime3bytes = 506832829
|
|
prime4bytes = 2654435761
|
|
prime5bytes = 889523592379
|
|
prime6bytes = 227718039650203
|
|
prime7bytes = 58295818150454627
|
|
prime8bytes = 0xcf1bbcdcb7a56463
|
|
)
|
|
|
|
// hashLen returns a hash of the lowest l bytes of u for a size size of h bytes.
|
|
// l must be >=4 and <=8. Any other value will return hash for 4 bytes.
|
|
// h should always be <32.
|
|
// Preferably h and l should be a constant.
|
|
// FIXME: This does NOT get resolved, if 'mls' is constant,
|
|
// so this cannot be used.
|
|
func hashLen(u uint64, hashLog, mls uint8) uint32 {
|
|
switch mls {
|
|
case 5:
|
|
return hash5(u, hashLog)
|
|
case 6:
|
|
return hash6(u, hashLog)
|
|
case 7:
|
|
return hash7(u, hashLog)
|
|
case 8:
|
|
return hash8(u, hashLog)
|
|
default:
|
|
return hash4x64(u, hashLog)
|
|
}
|
|
}
|
|
|
|
// hash3 returns the hash of the lower 3 bytes of u to fit in a hash table with h bits.
|
|
// Preferably h should be a constant and should always be <32.
|
|
func hash3(u uint32, h uint8) uint32 {
|
|
return ((u << (32 - 24)) * prime3bytes) >> ((32 - h) & 31)
|
|
}
|
|
|
|
// hash4 returns the hash of u to fit in a hash table with h bits.
|
|
// Preferably h should be a constant and should always be <32.
|
|
func hash4(u uint32, h uint8) uint32 {
|
|
return (u * prime4bytes) >> ((32 - h) & 31)
|
|
}
|
|
|
|
// hash4x64 returns the hash of the lowest 4 bytes of u to fit in a hash table with h bits.
|
|
// Preferably h should be a constant and should always be <32.
|
|
func hash4x64(u uint64, h uint8) uint32 {
|
|
return (uint32(u) * prime4bytes) >> ((32 - h) & 31)
|
|
}
|
|
|
|
// hash5 returns the hash of the lowest 5 bytes of u to fit in a hash table with h bits.
|
|
// Preferably h should be a constant and should always be <64.
|
|
func hash5(u uint64, h uint8) uint32 {
|
|
return uint32(((u << (64 - 40)) * prime5bytes) >> ((64 - h) & 63))
|
|
}
|
|
|
|
// hash6 returns the hash of the lowest 6 bytes of u to fit in a hash table with h bits.
|
|
// Preferably h should be a constant and should always be <64.
|
|
func hash6(u uint64, h uint8) uint32 {
|
|
return uint32(((u << (64 - 48)) * prime6bytes) >> ((64 - h) & 63))
|
|
}
|
|
|
|
// hash7 returns the hash of the lowest 7 bytes of u to fit in a hash table with h bits.
|
|
// Preferably h should be a constant and should always be <64.
|
|
func hash7(u uint64, h uint8) uint32 {
|
|
return uint32(((u << (64 - 56)) * prime7bytes) >> ((64 - h) & 63))
|
|
}
|
|
|
|
// hash8 returns the hash of u to fit in a hash table with h bits.
|
|
// Preferably h should be a constant and should always be <64.
|
|
func hash8(u uint64, h uint8) uint32 {
|
|
return uint32((u * prime8bytes) >> ((64 - h) & 63))
|
|
}
|