forked from jshiffer/matterbridge
36 lines
1.1 KiB
Go
36 lines
1.1 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 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)
|
|
}
|
|
}
|