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/*
* Copyright (C) 2005-2023 Sebastiano Vigna
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package it.unimi.dsi.fastutil.io;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
/** Simple, fast and repositionable byte array input stream that multiplexes its content among several arrays.
*
* This class is significantly slower than {@link FastByteArrayInputStream},
* but it can hold 256 PiB of data. The relevant constructor is {@link #FastMultiByteArrayInputStream(InputStream, long)},
* which fetches a stream and loads it into a sequence of byte arrays.
*
* @author Sebastiano Vigna
* @author Paolo Boldi
s */
public class FastMultiByteArrayInputStream extends MeasurableInputStream implements RepositionableStream {
/** The number of bits of an array slice index. */
public static final int SLICE_BITS = 30;
/** The maximum length of an array slice. */
public static final int SLICE_SIZE = 1 << SLICE_BITS;
/** The mask to retrieve a slice offset. */
public static final int SLICE_MASK = SLICE_SIZE - 1;
/** The array of arrays backing the input stream, plus an additional {@code null} entry. */
public byte[][] array;
/** The current array. */
public byte[] current;
/** The number of valid bytes in {@link #array}. */
public long length;
/** The current position. */
private long position;
/** Creates a new multi-array input stream loading it from a measurable input stream.
*
* @param is the input stream that will fill the array.
*/
public FastMultiByteArrayInputStream(final MeasurableInputStream is) throws IOException {
this(is, is.length());
}
/** Creates a new multi-array input stream loading it from an input stream.
*
* @param is the input stream that will fill the array.
* @param size the number of bytes to be read from {@code is}.
*/
public FastMultiByteArrayInputStream(final InputStream is, long size) throws IOException {
length = size;
array = new byte[(int)((size + SLICE_SIZE - 1) / SLICE_SIZE) + 1][];
for(int i = 0; i < array.length - 1; i++) {
array[i] = new byte[size >= SLICE_SIZE ? SLICE_SIZE : (int)size];
// It is important *not* to use is.read() directly because of bug #6478546
if (read(is, array[i]) != array[i].length) throw new EOFException();
size -= array[i].length;
}
current = array[0];
}
private static long read(final InputStream is, final byte[] a) throws IOException {
if (a.length == 0) return 0L;
int read = 0, result;
do {
result = is.read(a, read, Math.min(a.length - read, 1024 * 1024));
if (result < 0) return read;
read += result;
} while(read < a.length);
return read;
}
/** Creates a new multi-array input stream sharing the backing arrays of another multi-array input stream.
*
* @param is the multi-array input stream to replicate.
*/
public FastMultiByteArrayInputStream(final FastMultiByteArrayInputStream is) {
this.array = is.array;
this.length = is.length;
this.current = array[0];
}
/** Creates a new multi-array input stream using a given array.
*
* @param array the backing array.
*/
public FastMultiByteArrayInputStream(final byte[] array) {
if (array.length == 0) this.array = new byte[1][];
else {
this.array = new byte[2][];
this.array[0] = array;
this.length = array.length;
this.current = array;
}
}
/** Returns the number of bytes that can be read (or skipped over) from this input stream without blocking.
*
* Note that this number may be smaller than the number of bytes actually
* available from the stream if this number exceeds {@link Integer#MAX_VALUE}.
*
* @return the minimum among the number of available bytes and {@link Integer#MAX_VALUE}.
*/
@Override
public int available() {
return (int)Math.min(Integer.MAX_VALUE, length - position);
}
@Override
public long skip(long n) {
if (n > length - position) n = length - position;
position += n;
updateCurrent();
return n;
}
@Override
public int read() {
if (length == position) return -1;
final int disp = (int)(position++ & SLICE_MASK);
if (disp == 0) updateCurrent();
return current[disp] & 0xFF;
}
@Override
public int read(final byte[] b, int offset, final int length) {
final long remaining = this.length - position;
if (remaining == 0) return length == 0 ? 0 : -1;
int n = (int)Math.min(length, remaining);
final int m = n;
for(;;) {
final int disp = (int)(position & SLICE_MASK);
if (disp == 0) updateCurrent();
final int res = Math.min(n, current.length - disp);
System.arraycopy(current, disp, b, offset, res);
n -= res;
position += res;
if (n == 0) return m;
offset += res;
}
}
private void updateCurrent() {
current = array[(int)(position >>> SLICE_BITS)];
}
@Override
public long position() {
return position;
}
@Override
public void position(final long newPosition) {
position = Math.min(newPosition, length);
updateCurrent();
}
@Override
public long length() throws IOException {
return length;
}
/** NOP. */
@Override
public void close() {}
@Override
public boolean markSupported() {
return false;
}
@Override
public void mark(final int dummy) {
throw new UnsupportedOperationException();
}
@Override
public void reset() {
throw new UnsupportedOperationException();
}
}