86 lines
2.1 KiB
Go
86 lines
2.1 KiB
Go
package filename
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import (
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"encoding/base64"
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"encoding/binary"
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"github.com/dop251/scsu"
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"github.com/klauspost/compress/huff0"
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)
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// Encode will encode the string and return a base64 (url) compatible version of it.
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// Calling Decode with the returned string should always succeed.
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// It is not a requirement that the input string is valid utf-8.
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func Encode(s string) string {
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table, payload := EncodeBytes(s)
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return string(encodeURL[table]) + base64.URLEncoding.EncodeToString(payload)
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}
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// EncodeBytes will compress the given string and return a table identifier and a payload.
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func EncodeBytes(s string) (table byte, payload []byte) {
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initCoders()
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bestSize := len(s)
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bestTable := byte(tableUncompressed)
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org := []byte(s)
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bestOut := []byte(s)
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// Try all tables and choose the best
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for i, enc := range encTables[:] {
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org := org
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if len(org) <= 1 || len(org) > maxLength {
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// Use the uncompressed
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break
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}
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if enc == nil {
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continue
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}
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if i == tableSCSU {
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var err error
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olen := len(org)
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org, err = scsu.EncodeStrict(s, make([]byte, 0, len(org)))
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if err != nil || olen <= len(org) {
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continue
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}
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if len(org) < bestSize {
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// This is already better, store so we can use if the table cannot.
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bestOut = bestOut[:len(org)]
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bestTable = tableSCSUPlain
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bestSize = len(org)
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copy(bestOut, org)
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}
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}
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// Try to encode using table.
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err := func() error {
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encTableLocks[i].Lock()
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defer encTableLocks[i].Unlock()
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out, _, err := huff0.Compress1X(org, enc)
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if err != nil {
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return err
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}
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if len(out) < bestSize {
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bestOut = bestOut[:len(out)]
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bestTable = byte(i)
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bestSize = len(out)
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copy(bestOut, out)
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}
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return nil
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}()
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// If input is a single byte repeated store as RLE or save uncompressed.
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if err == huff0.ErrUseRLE && i != tableSCSU {
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if len(org) > 2 {
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// Encode as one byte repeated since it will be smaller than uncompressed.
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n := binary.PutUvarint(bestOut, uint64(len(org)))
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bestOut = bestOut[:n+1]
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bestOut[n] = org[0]
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bestSize = n + 1
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bestTable = tableRLE
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}
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break
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}
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}
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return bestTable, bestOut
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}
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