github.com/stafiprotocol/go-substrate-rpc-client@v1.4.7/subkey/compact.go (about)

     1  // Copyright 2018 Jsgenesis
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package subkey
    16  
    17  import (
    18  	"bytes"
    19  	"encoding/binary"
    20  	"errors"
    21  )
    22  
    23  func compactUint(v uint64) ([]byte, error) {
    24  	// This code was copied over and adapted with many thanks from Joystream/parity-codec-go:withreflect@develop
    25  	var buf bytes.Buffer
    26  	if v < 1<<30 {
    27  		switch {
    28  		case v < 1<<6:
    29  			return []byte{byte(v) << 2}, nil
    30  		case v < 1<<14:
    31  			err := binary.Write(&buf, binary.LittleEndian, uint16(v<<2)+1)
    32  			if err != nil {
    33  				return nil, err
    34  			}
    35  		default:
    36  			err := binary.Write(&buf, binary.LittleEndian, uint32(v<<2)+2)
    37  			if err != nil {
    38  				return nil, err
    39  			}
    40  		}
    41  		return buf.Bytes(), nil
    42  	}
    43  
    44  	n := byte(0)
    45  	limit := uint64(1 << 32)
    46  	for v >= limit && limit > 256 { // when overflows, limit will be < 256
    47  		n++
    48  		limit <<= 8
    49  	}
    50  	if n > 4 {
    51  		return nil, errors.New("assertion error: n>4 needed to compact-encode uint64")
    52  	}
    53  
    54  	err := buf.WriteByte((n << 2) + 3)
    55  	if err != nil {
    56  		return nil, err
    57  	}
    58  
    59  	b := make([]byte, 8)
    60  	binary.LittleEndian.PutUint64(b, v)
    61  	_, err = buf.Write(b[:4+n])
    62  	if err != nil {
    63  		return nil, err
    64  	}
    65  	return buf.Bytes(), nil
    66  }