gtsocial-umbx

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compress.go (1122B)

      1 // Copyright 2011 The Go Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style
      3 // license that can be found in the LICENSE file.
      4 
      5 package tiff
      6 
      7 import (
      8 	"bufio"
      9 	"io"
     10 )
     11 
     12 type byteReader interface {
     13 	io.Reader
     14 	io.ByteReader
     15 }
     16 
     17 // unpackBits decodes the PackBits-compressed data in src and returns the
     18 // uncompressed data.
     19 //
     20 // The PackBits compression format is described in section 9 (p. 42)
     21 // of the TIFF spec.
     22 func unpackBits(r io.Reader) ([]byte, error) {
     23 	buf := make([]byte, 128)
     24 	dst := make([]byte, 0, 1024)
     25 	br, ok := r.(byteReader)
     26 	if !ok {
     27 		br = bufio.NewReader(r)
     28 	}
     29 
     30 	for {
     31 		b, err := br.ReadByte()
     32 		if err != nil {
     33 			if err == io.EOF {
     34 				return dst, nil
     35 			}
     36 			return nil, err
     37 		}
     38 		code := int(int8(b))
     39 		switch {
     40 		case code >= 0:
     41 			n, err := io.ReadFull(br, buf[:code+1])
     42 			if err != nil {
     43 				return nil, err
     44 			}
     45 			dst = append(dst, buf[:n]...)
     46 		case code == -128:
     47 			// No-op.
     48 		default:
     49 			if b, err = br.ReadByte(); err != nil {
     50 				return nil, err
     51 			}
     52 			for j := 0; j < 1-code; j++ {
     53 				buf[j] = b
     54 			}
     55 			dst = append(dst, buf[:1-code]...)
     56 		}
     57 	}
     58 }