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compact.go
66 lines (60 loc) · 1.61 KB
/
compact.go
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// Copyright 2018 Jsgenesis
//
// 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,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package subkey
import (
"bytes"
"encoding/binary"
"errors"
)
func compactUint(v uint64) ([]byte, error) {
// This code was copied over and adapted with many thanks from Joystream/parity-codec-go:withreflect@develop
var buf bytes.Buffer
if v < 1<<30 {
switch {
case v < 1<<6:
return []byte{byte(v) << 2}, nil
case v < 1<<14:
err := binary.Write(&buf, binary.LittleEndian, uint16(v<<2)+1)
if err != nil {
return nil, err
}
default:
err := binary.Write(&buf, binary.LittleEndian, uint32(v<<2)+2)
if err != nil {
return nil, err
}
}
return buf.Bytes(), nil
}
n := byte(0)
limit := uint64(1 << 32)
for v >= limit && limit > 256 { // when overflows, limit will be < 256
n++
limit <<= 8
}
if n > 4 {
return nil, errors.New("assertion error: n>4 needed to compact-encode uint64")
}
err := buf.WriteByte((n << 2) + 3)
if err != nil {
return nil, err
}
b := make([]byte, 8)
binary.LittleEndian.PutUint64(b, v)
_, err = buf.Write(b[:4+n])
if err != nil {
return nil, err
}
return buf.Bytes(), nil
}