| // 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 mls bytes of with length output bits. |
| // mls must be >=3 and <=8. Any other value will return hash for 4 bytes. |
| // length should always be < 32. |
| // Preferably length and mls should be a constant for inlining. |
| func hashLen(u uint64, length, mls uint8) uint32 { |
| switch mls { |
| case 3: |
| return (uint32(u<<8) * prime3bytes) >> (32 - length) |
| case 5: |
| return uint32(((u << (64 - 40)) * prime5bytes) >> (64 - length)) |
| case 6: |
| return uint32(((u << (64 - 48)) * prime6bytes) >> (64 - length)) |
| case 7: |
| return uint32(((u << (64 - 56)) * prime7bytes) >> (64 - length)) |
| case 8: |
| return uint32((u * prime8bytes) >> (64 - length)) |
| default: |
| return (uint32(u) * prime4bytes) >> (32 - length) |
| } |
| } |
| |
| // 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) |
| } |