Fast Input Code Bug

[knightry]

So I've written this up in Java and am getting mixed results. I don't quite know how to explain it. I have submitted it many times on INTEST, and about 20% of the time is gets ACC in ~1.85 seconds, and the rest of the time it gets WA. I'm at a loss. Anybody see anything wrong with this? I'm by no means an expert on efficient input in Java, so there may be something very stupid I'm doing here...

[code]
final int BUFSIZE = 1 << 16;
BufferedInputStream sin = null;
byte[] buffer = new byte[BUFSIZE];
int bufptr = 0;

void open() throws Exception
{
	sin = new BufferedInputStream(System.in, BUFSIZE);
	init();
}

void init() throws Exception
{
	bufptr = 0;
	sin.read(buffer, 0, BUFSIZE);
}

int nextInt() throws Exception
{
	int ret = 0;
	byte c = read();
	boolean neg = false;
	if (c == '-')
	{
		neg = true;
		c = read();
	}
	if (c == '+')
		c = read();
	while (c <= ' ')
		c = read();
	ret = c - '0';
	c = read();
	while (c >= '0' && c <= '9')
	{
		ret *= 10;
		ret += c - '0';
		c = read();
	}
	if (neg)
		return -ret;
	return ret;
}

byte read() throws Exception
{
	if (bufptr == BUFSIZE)
		init();
	byte c = buffer[bufptr++];
	return c;
}[/code]

[knightry]

Well, I figured out what I was doing wrong. I was handling the case incorrectly where the there were less bytes left to be read than the size of the buffer. I have fixed it. I'm posting my code below for any other Java programmers who want to be able to do input efficiently. Note that it only has nextInt(), so you'll have to implement other data types if you need those for your problem. Also, I have chosen the buffer size by empirically testing a range of values. This proved to be the best in my testing. YMMV. Enjoy!

import java.io.DataInputStream;
import java.io.InputStream;
class Parser
{
	final private int BUFFER_SIZE = 1 << 16;
    private DataInputStream din;
private byte[] buffer;
private int bufferPointer, bytesRead;

public Parser(InputStream in)
{
	din = new DataInputStream(in);
	buffer = new byte[BUFFER_SIZE];
	bufferPointer = bytesRead = 0;
}

public int nextInt() throws Exception
{
	int ret = 0;
	byte c = read();
	while (c <= ' ') c = read();
	boolean neg = c == '-';
	if (neg) c = read();
	do
	{
		ret = ret * 10 + c - '0';
		c = read();
	} while (c > ' ');
	if (neg) return -ret;
	return ret;
}

private void fillBuffer() throws Exception
{
	bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
	if (bytesRead == -1) buffer[0] = -1;
}

private byte read() throws Exception
{
	if (bufferPointer == bytesRead) fillBuffer();
	return buffer[bufferPointer++];
}
}

[congcsbsju]

Hmm... its not working for me with the INTEST problem. Any idea?

[congcsbsju]

But its working now with second try. Hmm... is this stable?

[knightry]

Did you make sure to use the 2nd code, not the 1st? The first one posted is NOT stable, the 2nd one should be, I have been using it on this site with success, as well as on UVa and USACO with no problems.