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/*
 * Copyright (c) 2012.  Peter Lawrey
 *
 * "THE BEER-WARE LICENSE" (Revision 128)
 * As long as you retain this notice you can do whatever you want with this stuff.
 * If we meet some day, and you think this stuff is worth it, you can buy me a beer in return
 * There is no warranty.
 */

package com.google.code.java.core.io;

import org.junit.Test;

import java.io.*;

public class BufferTest {
    public static final double RUN_TIME_NS = 1e9;

    @Test
    public void testBufferPerformance() throws IOException {
        for (int i = 1; i <= 1024 * 1024; i *= 2) {
            testBufferSize(i);
        }
    }

    private static void testBufferSize(int size) throws IOException {
        int fileSize = 16 * 1024 * 1024;

        byte[] bytes = new byte[size];
        File tmpFile = File.createTempFile("deleteme", "zeros");
        tmpFile.deleteOnExit();

        // test writing an unbuffered file.
        int count1 = 0;
        long start1 = System.nanoTime();
        do {
            count1++;
            OutputStream out = new FileOutputStream(tmpFile);
            for (int i = 0; i < fileSize; i += size)
                out.write(bytes);
            out.close();
        } while (start1 + RUN_TIME_NS > System.nanoTime());
        long time1 = (System.nanoTime() - start1) / count1;

        // test writing a buffered file.
        int count2 = 0;
        long start2 = System.nanoTime();
        do {
            count2++;
            OutputStream out = new BufferedOutputStream(new FileOutputStream(tmpFile));
            for (int i = 0; i < fileSize; i += size)
                out.write(bytes);
            out.close();
        } while (start2 + RUN_TIME_NS > System.nanoTime());
        long time2 = (System.nanoTime() - start2) / count2;

        // test reading unbuffered file.
        int count3 = 0;
        long start3 = System.nanoTime();
        do {
            count3++;
            InputStream in = new FileInputStream(tmpFile);
            while (in.read(bytes) > 0) ;
            in.close();
        } while (start3 + RUN_TIME_NS > System.nanoTime());
        long time3 = (System.nanoTime() - start3) / count3;

        // test reading buffered file.
        int count4 = 0;
        long start4 = System.nanoTime();
        do {
            count4++;
            InputStream in = new BufferedInputStream(new FileInputStream(tmpFile));
            while (in.read(bytes) > 0) ;
            in.close();
        } while (start4 + RUN_TIME_NS > System.nanoTime());
        long time4 = (System.nanoTime() - start4) / count4;

        long factor = 16 * 1000 * 1000 * 1000L; // 16 MB/ns in MB/s
        System.out.printf("<tr><td align=\"right\">%,d"
                + "</td><td align=\"right\">%,d MB/s"
                + "</td><td align=\"right\">%,d MB/s"
                + "</td><td align=\"right\">%,d MB/s"
                + "</td><td align=\"right\">%,d MB/s"
                + "</td></tr>%n", size,
                factor / time1, factor / time2, factor / time3, factor / time4
        );
    }
}