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183 lines
4.1 KiB
183 lines
4.1 KiB
// Copyright 2015 PingCAP, 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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// See the License for the specific language governing permissions and
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// limitations under the License.
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package codec
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import (
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"bytes"
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"math/big"
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"github.com/juju/errors"
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"github.com/pingcap/tidb/mysql"
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)
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const (
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negativeSign int64 = 8
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zeroSign int64 = 16
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positiveSign int64 = 24
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)
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func codecSign(value int64) int64 {
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if value < 0 {
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return negativeSign
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}
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return positiveSign
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}
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func encodeExp(expValue int64, expSign int64, valSign int64) int64 {
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if expSign == negativeSign {
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expValue = -expValue
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}
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if expSign != valSign {
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expValue = ^expValue
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}
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return expValue
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}
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func decodeExp(expValue int64, expSign int64, valSign int64) int64 {
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if expSign != valSign {
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expValue = ^expValue
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}
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if expSign == negativeSign {
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expValue = -expValue
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}
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return expValue
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}
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func codecValue(value []byte, valSign int64) {
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if valSign == negativeSign {
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reverseBytes(value)
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}
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}
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// EncodeDecimal encodes a decimal d into a byte slice which can be sorted lexicographically later.
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// EncodeDecimal guarantees that the encoded value is in ascending order for comparison.
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// Decimal encoding:
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// Byte -> value sign
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// Byte -> exp sign
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// EncodeInt -> exp value
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// EncodeBytes -> abs value bytes
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func EncodeDecimal(b []byte, d mysql.Decimal) []byte {
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if d.Equals(mysql.ZeroDecimal) {
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return append(b, byte(zeroSign))
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}
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v := d.BigIntValue()
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valSign := codecSign(int64(v.Sign()))
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absVal := new(big.Int)
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absVal.Abs(v)
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value := []byte(absVal.String())
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// Trim right side "0", like "12.34000" -> "12.34" or "0.1234000" -> "0.1234".
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if d.Exponent() != 0 {
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value = bytes.TrimRight(value, "0")
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}
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// Get exp and value, format is "value":"exp".
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// like "12.34" -> "0.1234":"2".
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// like "-0.01234" -> "-0.1234":"-1".
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exp := int64(0)
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div := big.NewInt(10)
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for ; ; exp++ {
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if absVal.Sign() == 0 {
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break
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}
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absVal = absVal.Div(absVal, div)
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}
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expVal := exp + int64(d.Exponent())
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expSign := codecSign(expVal)
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// For negtive exp, do bit reverse for exp.
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// For negtive decimal, do bit reverse for exp and value.
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expVal = encodeExp(expVal, expSign, valSign)
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codecValue(value, valSign)
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b = append(b, byte(valSign))
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b = append(b, byte(expSign))
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b = EncodeInt(b, expVal)
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b = EncodeBytes(b, value)
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return b
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}
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// DecodeDecimal decodes bytes to decimal.
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// DecodeFloat decodes a float from a byte slice
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// Decimal decoding:
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// Byte -> value sign
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// Byte -> exp sign
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// DecodeInt -> exp value
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// DecodeBytes -> abs value bytes
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func DecodeDecimal(b []byte) ([]byte, mysql.Decimal, error) {
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var (
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r = b
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d mysql.Decimal
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err error
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)
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// Decode value sign.
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valSign := int64(r[0])
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r = r[1:]
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if valSign == zeroSign {
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d, err = mysql.ParseDecimal("0")
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return r, d, errors.Trace(err)
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}
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// Decode exp sign.
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expSign := int64(r[0])
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r = r[1:]
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// Decode exp value.
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expVal := int64(0)
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r, expVal, err = DecodeInt(r)
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if err != nil {
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return r, d, errors.Trace(err)
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}
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expVal = decodeExp(expVal, expSign, valSign)
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// Decode abs value bytes.
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value := []byte{}
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r, value, err = DecodeBytes(r)
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if err != nil {
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return r, d, errors.Trace(err)
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}
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codecValue(value, valSign)
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// Generate decimal string value.
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var decimalStr []byte
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if valSign == negativeSign {
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decimalStr = append(decimalStr, '-')
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}
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if expVal <= 0 {
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// Like decimal "0.1234" or "0.01234".
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decimalStr = append(decimalStr, '0')
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decimalStr = append(decimalStr, '.')
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decimalStr = append(decimalStr, bytes.Repeat([]byte{'0'}, -int(expVal))...)
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decimalStr = append(decimalStr, value...)
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} else {
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// Like decimal "12.34".
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decimalStr = append(decimalStr, value[:expVal]...)
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decimalStr = append(decimalStr, '.')
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decimalStr = append(decimalStr, value[expVal:]...)
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}
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d, err = mysql.ParseDecimal(string(decimalStr))
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return r, d, errors.Trace(err)
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}
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