func DecodeCmpUintToInt(u uint64) int64 {
	return int64(u ^ signMask)
}
DecodeCmpUintToInt decodes the u that encoded by EncodeIntToCmpUint
package codec
import (
	"encoding/binary"
	"math"
	"github.com/pingcap/errors"
)
const signMask uint64 = 0x8000000000000000
func EncodeIntToCmpUint(v int64) uint64 {
	return uint64(v) ^ signMask
}