108 lines
2.6 KiB
Go
108 lines
2.6 KiB
Go
/*
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Copyright 2022 Alibaba Group Holding Limited.
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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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http://www.apache.org/licenses/LICENSE-2.0
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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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*/
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package rows
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import (
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"encoding/binary"
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"errors"
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"math/big"
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"github.com/shopspring/decimal"
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)
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// MYSQL_TYPE_NEWDECIMAL
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var digitsBytesNumMap = []int{0, 1, 1, 2, 2, 3, 3, 4, 4, 4}
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func decimalBytesNumber(numDigits int) int {
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return 4*(numDigits/9) + digitsBytesNumMap[numDigits%9]
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}
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func readBigEndianNumber(bs []byte, numBytes int) uint64 {
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switch numBytes {
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case 1:
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return uint64(bs[0])
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case 2:
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return uint64(binary.BigEndian.Uint16(bs))
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case 3:
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return uint64(uint32(bs[0])<<16 | uint32(bs[1])<<8 | uint32(bs[2]))
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case 4:
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return uint64(binary.BigEndian.Uint32(bs))
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case 8:
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return binary.BigEndian.Uint64(bs)
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default:
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panic("never reach here")
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}
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}
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func parseDecimalPart(bs []byte) *big.Int {
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oneBillion := big.NewInt(1000000000)
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r := big.NewInt(0)
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left := len(bs) & 0x3
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if left > 0 {
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r.Add(r, big.NewInt(0).SetUint64(readBigEndianNumber(bs, left)))
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}
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for i := left; i < len(bs); i += 4 {
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x := binary.BigEndian.Uint32(bs[i:])
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r.Mul(r, oneBillion)
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r.Add(r, big.NewInt(0).SetUint64(uint64(x)))
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}
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return r
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}
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func fastExp(x *big.Int, exp byte) *big.Int {
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r := big.NewInt(1)
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a := big.NewInt(0).Set(x)
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for exp > 0 {
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if exp&0x1 != 0 {
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r.Mul(r, a)
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}
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a.Mul(a, a)
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exp >>= 1
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}
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return r
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}
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func ExtractNewDecimalFromBlock(bs []byte, precision byte, scale byte) (decimal.Decimal, int, error) {
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intPartLen, fracPartLen := decimalBytesNumber(int(precision-scale)), decimalBytesNumber(int(scale))
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bytesLen := intPartLen + fracPartLen
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if len(bs) < bytesLen {
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return decimal.Decimal{}, 0, errors.New("not enough bytes")
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}
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negative := (bs[0] & 0x80) == 0
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buf := make([]byte, bytesLen)
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copy(buf, bs[:bytesLen])
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if negative {
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for i := range buf {
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buf[i] = ^buf[i]
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}
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}
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buf[0] &= 0x7f
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intPart := parseDecimalPart(buf[:intPartLen])
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fracPart := parseDecimalPart(buf[intPartLen:bytesLen])
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r := big.NewInt(0).Set(intPart)
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r.Mul(r, fastExp(big.NewInt(10), scale))
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r.Add(r, fracPart)
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if negative {
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r.Neg(r)
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}
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return decimal.NewFromBigInt(r, -int32(scale)), bytesLen, nil
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}
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