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