95 lines
3.3 KiB
Go
95 lines
3.3 KiB
Go
// Copyright 2014 The Cockroach Authors.
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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
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// implied. See the License for the specific language governing
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// permissions and limitations under the License.
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// This code originated from:
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// https://github.com/cockroachdb/cockroach/blob/2dd65dde5d90c157f4b93f92502ca1063b904e1d/pkg/util/encoding/encoding.go
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// Modified to not use pkg/errors
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package segment
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import "fmt"
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const (
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MaxVarintSize = 9
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// IntMin is chosen such that the range of int tags does not overlap the
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// ascii character set that is frequently used in testing.
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IntMin = 0x80 // 128
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intMaxWidth = 8
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intZero = IntMin + intMaxWidth // 136
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intSmall = IntMax - intZero - intMaxWidth // 109
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// IntMax is the maximum int tag value.
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IntMax = 0xfd // 253
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)
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// EncodeUvarintAscending encodes the uint64 value using a variable length
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// (length-prefixed) representation. The length is encoded as a single
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// byte indicating the number of encoded bytes (-8) to follow. See
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// EncodeVarintAscending for rationale. The encoded bytes are appended to the
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// supplied buffer and the final buffer is returned.
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func EncodeUvarintAscending(b []byte, v uint64) []byte {
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switch {
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case v <= intSmall:
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return append(b, intZero+byte(v))
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case v <= 0xff:
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return append(b, IntMax-7, byte(v))
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case v <= 0xffff:
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return append(b, IntMax-6, byte(v>>8), byte(v))
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case v <= 0xffffff:
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return append(b, IntMax-5, byte(v>>16), byte(v>>8), byte(v))
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case v <= 0xffffffff:
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return append(b, IntMax-4, byte(v>>24), byte(v>>16), byte(v>>8), byte(v))
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case v <= 0xffffffffff:
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return append(b, IntMax-3, byte(v>>32), byte(v>>24), byte(v>>16), byte(v>>8),
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byte(v))
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case v <= 0xffffffffffff:
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return append(b, IntMax-2, byte(v>>40), byte(v>>32), byte(v>>24), byte(v>>16),
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byte(v>>8), byte(v))
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case v <= 0xffffffffffffff:
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return append(b, IntMax-1, byte(v>>48), byte(v>>40), byte(v>>32), byte(v>>24),
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byte(v>>16), byte(v>>8), byte(v))
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default:
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return append(b, IntMax, byte(v>>56), byte(v>>48), byte(v>>40), byte(v>>32),
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byte(v>>24), byte(v>>16), byte(v>>8), byte(v))
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}
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}
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// DecodeUvarintAscending decodes a varint encoded uint64 from the input
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// buffer. The remainder of the input buffer and the decoded uint64
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// are returned.
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func DecodeUvarintAscending(b []byte) ([]byte, uint64, error) {
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if len(b) == 0 {
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return nil, 0, fmt.Errorf("insufficient bytes to decode uvarint value")
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}
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length := int(b[0]) - intZero
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b = b[1:] // skip length byte
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if length <= intSmall {
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return b, uint64(length), nil
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}
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length -= intSmall
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if length < 0 || length > 8 {
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return nil, 0, fmt.Errorf("invalid uvarint length of %d", length)
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} else if len(b) < length {
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return nil, 0, fmt.Errorf("insufficient bytes to decode uvarint value: %q", b)
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}
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var v uint64
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// It is faster to range over the elements in a slice than to index
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// into the slice on each loop iteration.
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for _, t := range b[:length] {
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v = (v << 8) | uint64(t)
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}
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return b[length:], v, nil
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}
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