Package org.jpedal.io.filter

Class ASCII85InputStream

java.lang.Object

java.io.InputStream

java.io.FilterInputStream

org.jpedal.io.filter.ASCII85InputStream

All Implemented Interfaces:

Closeable, AutoCloseable

public class ASCII85InputStream
extends FilterInputStream

An input stream that decodes bytes from an ASCII string using the ASCII 85 filter

ASCII base-85 decoding shall produce 4 bytes of binary data for every 5 ASCII characters.
Each group of 5 output bytes (c1, c2, c3, c4, c5) shall be converted to a group of 4 binary input bytes (b1, b2, b3, b4) using the relation:

  (b1 * 256^3) + (b2 * 256^2) + (b3 * 256) + b4
      = (c1 * 85^4) + (c2 * 85 ^ 3) + (c3 * 85^2) + (c4 * 85) + c5
 

In other words, 1 ascii z character will be reinterpreted as 5 0 numbers or 5 ASCII in the range 33 (!) to 117 (u) characters will each subtract 33 (the ASCII code for the character !), the resulting numbers from either of these will then be interpreted as a single base-85 number. This will then be converted to a base 256 number, the bytes of which will be the 4 output bytes

If the length of the data to be decoded is not a multiple of 5 bytes, the last, partial group of 5 shall be used to produce a last, partial group of 4 output characters. Given n (1, 2, 3, or 4) bytes of binary data, the decoder shall first append 5 - n zero bytes to make a complete group of 5. It shall decode this group in the usual way. Finally, it shall read only the first n - 1 characters of the resulting group of 4.
- PDF Spec ISO 32000-2

Constructor Summary

Constructors

Constructor	Description
ASCII85InputStream(InputStream in)

Method Summary

Modifier and Type	Method	Description
int	available()
boolean	markSupported()
int	read()
int	read(byte[] outputBytes, int outputOffset, int byteCount)
long	skip(long n)

Methods inherited from class java.io.FilterInputStream

close, mark, read, reset

Methods inherited from class java.io.InputStream

nullInputStream, readAllBytes, readNBytes, readNBytes, skipNBytes, transferTo

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

ASCII85InputStream

public ASCII85InputStream(InputStream in)

Method Details

skip

public long skip(long n)
          throws IOException

Overrides:

skip in class FilterInputStream

Throws:

IOException

read

public int read()
         throws IOException

Overrides:

read in class FilterInputStream

Throws:

IOException

read

public int read(byte[] outputBytes,
 int outputOffset,
 int byteCount)
         throws IOException

Overrides:

read in class FilterInputStream

Throws:

IOException

available

public int available()
              throws IOException

Overrides:

available in class FilterInputStream

Throws:

IOException

markSupported

public boolean markSupported()

Overrides:

markSupported in class FilterInputStream