| // 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)) |
| } |