gopar3.go

package gopar3

import (
	"context"
	"hash/crc32"
	"io"
)

const (
	ShardLimit      = 1<<(TagBytesForShardOrder*8) - 1
	ShardBatchLimit = 1<<(TagBytesForShardBatch*8) - 1
	SourceSizeLimit = 1<<(TagBytesForSourceSize*8) - 1
)

// castagnoliTable sources [crc.New] with 0x82f63b78
// polynomial. It is known for superior error detection
// and use in BitTorrent and iSCSI protocols.
//
// Example of BitTorrent use:
// https://github.com/anacrolix/torrent/blob/master/bep40.go
var castagnoliTable = crc32.MakeTable(crc32.Castagnoli)

func CastagnoliSum(ctx context.Context, r io.Reader) (uint32, error) {
	var (
		crc  = crc32.New(castagnoliTable)
		b    = make([]byte, 2*32*1024)
		n    int
		rerr error
		werr error
	)
	for rerr == nil {
		select {
		case <-ctx.Done():
			return 0, ctx.Err()
		default:
		}

		n, rerr = io.ReadFull(r, b)
		if _, werr = crc.Write(b[:n]); werr != nil {
			return 0, werr
		}
		switch rerr {
		case io.EOF, io.ErrUnexpectedEOF:
		default:
			return 0, rerr
		}
	}
	return crc.Sum32(), nil
}