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position_inertia.go
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position_inertia.go
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// Copyright 2020 PingCAP, 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,
// See the License for the specific language governing permissions and
// limitations under the License.
package hash
import (
"hash"
"hash/crc32"
"github.com/pingcap/log"
"go.uber.org/zap"
)
const hashMagicNumber = 0
// PositionInertia is a 8-bits hash which is bytes partitions inertia
type PositionInertia struct {
hashValue uint32
hasher hash.Hash32
}
// NewPositionInertia creates a new position inertia algorithm hash builder
func NewPositionInertia() *PositionInertia {
return &PositionInertia{
hashValue: hashMagicNumber,
hasher: crc32.NewIEEE(),
}
}
// Write writes the bytes into the PositionInertia
func (p *PositionInertia) Write(bss ...[]byte) {
p.hasher.Reset()
for _, bs := range bss {
_, err := p.hasher.Write(bs)
if err != nil {
log.Panic("failed to write hash", zap.Error(err))
}
}
rawHash := p.hasher.Sum32()
p.hashValue ^= rawHash
}
// Sum32 returns the 32-bits hash
func (p *PositionInertia) Sum32() uint32 {
return p.hashValue
}
// Reset resets the PositionInertia
func (p *PositionInertia) Reset() {
p.hashValue = hashMagicNumber
}