75 lines
2.1 KiB
Go
75 lines
2.1 KiB
Go
|
// Copyright (c) 2014 Couchbase, Inc.
|
||
|
|
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
|
||
|
|
// except in compliance with the License. You may obtain a copy of the License at
|
||
|
|
// http://www.apache.org/licenses/LICENSE-2.0
|
||
|
|
// Unless required by applicable law or agreed to in writing, software distributed under the
|
||
|
|
// License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
|
||
|
|
// either express or implied. See the License for the specific language governing permissions
|
||
|
|
// and limitations under the License.
|
||
|
|
|
||
|
|
package numeric_util
|
||
|
|
|
||
|
|
import (
|
||
|
|
"fmt"
|
||
|
|
)
|
||
|
|
|
||
|
|
const ShiftStartInt64 byte = 0x20
|
||
|
|
|
||
|
|
// PrefixCoded is a byte array encoding of
|
||
|
|
// 64-bit numeric values shifted by 0-63 bits
|
||
|
|
type PrefixCoded []byte
|
||
|
|
|
||
|
|
func NewPrefixCodedInt64(in int64, shift uint) (PrefixCoded, error) {
|
||
|
|
if shift > 63 {
|
||
|
|
return nil, fmt.Errorf("cannot shift %d, must be between 0 and 63", shift)
|
||
|
|
}
|
||
|
|
|
||
|
|
nChars := (((63 - shift) * 37) >> 8) + 1
|
||
|
|
rv := make(PrefixCoded, nChars+1)
|
||
|
|
rv[0] = ShiftStartInt64 + byte(shift)
|
||
|
|
|
||
|
|
sortableBits := int64(uint64(in) ^ 0x8000000000000000)
|
||
|
|
sortableBits = int64(uint64(sortableBits) >> shift)
|
||
|
|
for nChars > 0 {
|
||
|
|
// Store 7 bits per byte for compatibility
|
||
|
|
// with UTF-8 encoding of terms
|
||
|
|
rv[nChars] = byte(sortableBits & 0x7f)
|
||
|
|
nChars--
|
||
|
|
sortableBits = int64(uint64(sortableBits) >> 7)
|
||
|
|
}
|
||
|
|
return rv, nil
|
||
|
|
}
|
||
|
|
|
||
|
|
func MustNewPrefixCodedInt64(in int64, shift uint) PrefixCoded {
|
||
|
|
rv, err := NewPrefixCodedInt64(in, shift)
|
||
|
|
if err != nil {
|
||
|
|
panic(err)
|
||
|
|
}
|
||
|
|
return rv
|
||
|
|
}
|
||
|
|
|
||
|
|
// Shift returns the number of bits shifted
|
||
|
|
// returns 0 if in uninitialized state
|
||
|
|
func (p PrefixCoded) Shift() (uint, error) {
|
||
|
|
if len(p) > 0 {
|
||
|
|
shift := p[0] - ShiftStartInt64
|
||
|
|
if shift < 0 || shift < 63 {
|
||
|
|
return uint(shift), nil
|
||
|
|
}
|
||
|
|
}
|
||
|
|
return 0, fmt.Errorf("invalid prefix coded value")
|
||
|
|
}
|
||
|
|
|
||
|
|
func (p PrefixCoded) Int64() (int64, error) {
|
||
|
|
shift, err := p.Shift()
|
||
|
|
if err != nil {
|
||
|
|
return 0, err
|
||
|
|
}
|
||
|
|
var sortableBits int64
|
||
|
|
for _, inbyte := range p[1:] {
|
||
|
|
sortableBits <<= 7
|
||
|
|
sortableBits |= int64(inbyte)
|
||
|
|
}
|
||
|
|
return int64(uint64((sortableBits << shift)) ^ 0x8000000000000000), nil
|
||
|
|
}
|