compress.go

Documentation: golang.org/x/image/tiff

     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  }
    59
View as plain text