forgejo/vendor/github.com/blevesearch/bleve/numeric/prefix_coded.go
2019-11-27 11:23:33 +02:00

112 lines
2.8 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
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) {
rv, _, err := NewPrefixCodedInt64Prealloc(in, shift, nil)
return rv, err
}
func NewPrefixCodedInt64Prealloc(in int64, shift uint, prealloc []byte) (
rv PrefixCoded, preallocRest []byte, err error) {
if shift > 63 {
return nil, prealloc, fmt.Errorf("cannot shift %d, must be between 0 and 63", shift)
}
nChars := ((63 - shift) / 7) + 1
size := int(nChars + 1)
if len(prealloc) >= size {
rv = PrefixCoded(prealloc[0:size])
preallocRest = prealloc[size:]
} else {
rv = make(PrefixCoded, size)
}
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, preallocRest, 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
}
func ValidPrefixCodedTerm(p string) (bool, int) {
return ValidPrefixCodedTermBytes([]byte(p))
}
func ValidPrefixCodedTermBytes(p []byte) (bool, int) {
if len(p) > 0 {
if p[0] < ShiftStartInt64 || p[0] > ShiftStartInt64+63 {
return false, 0
}
shift := p[0] - ShiftStartInt64
nChars := ((63 - int(shift)) / 7) + 1
if len(p) != nChars+1 {
return false, 0
}
return true, int(shift)
}
return false, 0
}