p1/machine/Lib.java

// PART OF THE MACHINE SIMULATION. DO NOT CHANGE.

package nachos.machine;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.security.PrivilegedAction;
import java.util.Random;

/**
 * Thrown when an assertion fails.
 */
class AssertionFailureError extends Error {
    AssertionFailureError() {
	super();
    }

    AssertionFailureError(String message) {
	super(message);
    }
}

/**
 * Provides miscellaneous library routines.
 */
public final class Lib {
    /**
     * Prevent instantiation.
     */
    private Lib() {
    }

    private static Random random = null;

    /**
     * Seed the random number generater. May only be called once.
     *
     * @param	randomSeed	the seed for the random number generator.
     */
    public static void seedRandom(long randomSeed) {
	assertTrue(random == null);
	random = new Random(randomSeed);
    }
    
    /**
     * Return a random integer between 0 and <i>range - 1</i>. Must not be
     * called before <tt>seedRandom()</tt> seeds the random number generator.
     *
     * @param	range	a positive value specifying the number of possible
     *			return values.
     * @return	a random integer in the specified range.
     */
    public static int random(int range) {
	assertTrue(range > 0);
	return random.nextInt(range);
    }

    /**
     * Return a random double between 0.0 (inclusive) and 1.0 (exclusive).
     *
     * @return	a random double between 0.0 and 1.0.
     */
    public static double random() {
	return random.nextDouble();
    }

    /**
     * Asserts that <i>expression</i> is <tt>true</tt>. If not, then Nachos
     * exits with an error message.
     *
     * @param	expression	the expression to assert.
     */     
    public static void assertTrue(boolean expression) {
	if (!expression)
	    throw new AssertionFailureError();
    }

    /**
     * Asserts that <i>expression</i> is <tt>true</tt>. If not, then Nachos
     * exits with the specified error message.
     *
     * @param	expression	the expression to assert.
     * @param	message		the error message.
     */     
    public static void assertTrue(boolean expression, String message) {
	if (!expression)
	    throw new AssertionFailureError(message);
    }

    /**
     * Asserts that this call is never made. Same as <tt>assertTrue(false)</tt>.
     */
    public static void assertNotReached() {
	assertTrue(false);
    }
    
    /**
     * Asserts that this call is never made, with the specified error messsage.
     * Same as <tt>assertTrue(false, message)</tt>.
     *
     * @param	message	the error message.
     */
    public static void assertNotReached(String message) {
	assertTrue(false, message);
    }
    
    /**
     * Print <i>message</i> if <i>flag</i> was enabled on the command line. To
     * specify which flags to enable, use the -d command line option. For
     * example, to enable flags a, c, and e, do the following:
     *
     * <p>
     * <pre>nachos -d ace</pre>
     *
     * <p>
     * Nachos uses several debugging flags already, but you are encouraged to
     * add your own.
     *
     * @param	flag	the debug flag that must be set to print this message.
     * @param	message	the debug message.
     */
    public static void debug(char flag, String message) {
	if (test(flag))
	    System.out.println(message);
    }

    /**
     * Tests if <i>flag</i> was enabled on the command line.
     *
     * @param	flag	the debug flag to test.
     *
     * @return	<tt>true</tt> if this flag was enabled on the command line.
     */
    public static boolean test(char flag) {
	if (debugFlags == null)
	    return false;
	else if (debugFlags[(int) '+'])
	    return true;
	else if (flag >= 0 && flag < 0x80 && debugFlags[(int) flag])
	    return true;
	else
	    return false;
    }

    /**
     * Enable all the debug flags in <i>flagsString</i>.
     *
     * @param	flagsString	the flags to enable.
     */
    public static void enableDebugFlags(String flagsString) {
	if (debugFlags == null)
	    debugFlags = new boolean[0x80];

	char[] newFlags = flagsString.toCharArray();
	for (int i=0; i<newFlags.length; i++) {
	    char c = newFlags[i];
	    if (c >= 0 && c < 0x80)
		debugFlags[(int) c] = true;
	}
    }

    /** Debug flags specified on the command line. */
    private static boolean debugFlags[];

    /**
     * Read a file, verifying that the requested number of bytes is read, and
     * verifying that the read operation took a non-zero amount of time.
     *
     * @param	file		the file to read.
     * @param	position	the file offset at which to start reading.
     * @param	buf		the buffer in which to store the data.
     * @param	offset		the buffer offset at which storing begins.
     * @param	length		the number of bytes to read.
     */
    public static void strictReadFile(OpenFile file, int position,
				      byte[] buf, int offset, int length) {
	long startTime = Machine.timer().getTime();
	assertTrue(file.read(position, buf, offset, length) == length);
	long finishTime = Machine.timer().getTime();
	assertTrue(finishTime>startTime);	
    }

    /**
     * Load an entire file into memory.
     *
     * @param	file	the file to load.
     * @return	an array containing the contents of the entire file, or
     *		<tt>null</tt> if an error occurred.
     */
    public static byte[] loadFile(OpenFile file) {
	int startOffset = file.tell();

	int length = file.length();
	if (length < 0)
	    return null;

	byte[] data = new byte[length];

	file.seek(0);
	int amount = file.read(data, 0, length);
	file.seek(startOffset);

	if (amount == length)
	    return data;
	else
	    return null;
    }

    /**
     * Take a read-only snapshot of a file.
     *
     * @param	file	the file to take a snapshot of.
     * @return	a read-only snapshot of the file.
     */
    public static OpenFile cloneFile(OpenFile file) {
	OpenFile clone = new ArrayFile(loadFile(file));

	clone.seek(file.tell());
	
	return clone;
    }

    /**
     * Convert a short into its little-endian byte string representation.
     *
     * @param	array	the array in which to store the byte string.
     * @param	offset	the offset in the array where the string will start.
     * @param	value	the value to convert.
     */
    public static void bytesFromShort(byte[] array, int offset, short value) {
	array[offset+0] = (byte) ((value>>0)&0xFF);
	array[offset+1] = (byte) ((value>>8)&0xFF);
    }

    /**
     * Convert an int into its little-endian byte string representation.
     *
     * @param	array	the array in which to store the byte string.
     * @param	offset	the offset in the array where the string will start.
     * @param	value	the value to convert.
     */
    public static void bytesFromInt(byte[] array, int offset, int value) {
	array[offset+0] = (byte) ((value>>0) &0xFF);
	array[offset+1] = (byte) ((value>>8) &0xFF);
	array[offset+2] = (byte) ((value>>16)&0xFF);
	array[offset+3] = (byte) ((value>>24)&0xFF);
    }

    /**
     * Convert an int into its little-endian byte string representation, and
     * return an array containing it.
     *
     * @param	value	the value to convert.
     * @return	an array containing the byte string.
     */
    public static byte[] bytesFromInt(int value) {
	byte[] array = new byte[4];
	bytesFromInt(array, 0, value);
	return array;
    }

    /**
     * Convert an int into a little-endian byte string representation of the
     * specified length.
     *
     * @param	array	the array in which to store the byte string.
     * @param	offset	the offset in the array where the string will start.
     * @param	length	the number of bytes to store (must be 1, 2, or 4).
     * @param	value	the value to convert.
     */
    public static void bytesFromInt(byte[] array, int offset,
				    int length, int value) {
	assertTrue(length==1 || length==2 || length==4);

	switch (length) {
	case 1:
	    array[offset] = (byte) value;
	    break;
	case 2:
	    bytesFromShort(array, offset, (short) value);
	    break;
	case 4:
	    bytesFromInt(array, offset, value);
	    break;
	}
    }

    /**
     * Convert to a short from its little-endian byte string representation.
     *
     * @param	array	the array containing the byte string.
     * @param	offset	the offset of the byte string in the array.
     * @return	the corresponding short value.
     */
    public static short bytesToShort(byte[] array, int offset) {
	return (short) ((((short) array[offset+0] & 0xFF) << 0) |
			(((short) array[offset+1] & 0xFF) << 8));
    }

    /**
     * Convert to an unsigned short from its little-endian byte string
     * representation.
     *
     * @param	array	the array containing the byte string.
     * @param	offset	the offset of the byte string in the array.
     * @return	the corresponding short value.
     */
    public static int bytesToUnsignedShort(byte[] array, int offset) {
	return (((int) bytesToShort(array, offset)) & 0xFFFF);
    }

    /**
     * Convert to an int from its little-endian byte string representation.
     *
     * @param	array	the array containing the byte string.
     * @param	offset	the offset of the byte string in the array.
     * @return	the corresponding int value.
     */
    public static int bytesToInt(byte[] array, int offset) {
	return (int) ((((int) array[offset+0] & 0xFF) << 0)  |
		      (((int) array[offset+1] & 0xFF) << 8)  |
		      (((int) array[offset+2] & 0xFF) << 16) |
		      (((int) array[offset+3] & 0xFF) << 24));
    }
    
    /**
     * Convert to an int from a little-endian byte string representation of the
     * specified length.
     *
     * @param	array	the array containing the byte string.
     * @param	offset	the offset of the byte string in the array.
     * @param	length	the length of the byte string.
     * @return	the corresponding value.
     */
    public static int bytesToInt(byte[] array, int offset, int length) {
	assertTrue(length==1 || length==2 || length==4);

	switch (length) {
	case 1:
	    return array[offset];
	case 2:
	    return bytesToShort(array, offset);
	case 4:
	    return bytesToInt(array, offset);
	default:
	    return -1;
	}
    }

    /**
     * Convert to a string from a possibly null-terminated array of bytes.
     *
     * @param	array	the array containing the byte string.
     * @param	offset	the offset of the byte string in the array.
     * @param	length	the maximum length of the byte string.
     * @return	a string containing the specified bytes, up to and not
     *		including the null-terminator (if present).
     */
    public static String bytesToString(byte[] array, int offset, int length) {
	int i;
	for (i=0; i<length; i++) {
	    if (array[offset+i] == 0)
		break;
	}

	return new String(array, offset, i);
    }

    /** Mask out and shift a bit substring.
     *
     * @param	bits	the bit string.
     * @param	lowest	the first bit of the substring within the string.
     * @param	size	the number of bits in the substring.
     * @return	the substring.
     */
    public static int extract(int bits, int lowest, int size) {
	if (size == 32)
	    return (bits >> lowest);
	else
	    return ((bits >> lowest) & ((1<<size)-1));
    }

    /** Mask out and shift a bit substring.
     *
     * @param	bits	the bit string.
     * @param	lowest	the first bit of the substring within the string.
     * @param	size	the number of bits in the substring.
     * @return	the substring.
     */
    public static long extract(long bits, int lowest, int size) {
	if (size == 64)
	    return (bits >> lowest);
	else
	    return ((bits >> lowest) & ((1L<<size)-1));
    }

    /** Mask out and shift a bit substring; then sign extend the substring.
     *
     * @param	bits	the bit string.
     * @param	lowest	the first bit of the substring within the string.
     * @param	size	the number of bits in the substring.
     * @return	the substring, sign-extended.
     */
    public static int extend(int bits, int lowest, int size) {
	int extra = 32 - (lowest+size);
	return ((extract(bits, lowest, size) << extra) >> extra);
    }

    /** Test if a bit is set in a bit string.
     *
     * @param	flag	the flag to test.
     * @param	bits	the bit string.
     * @return	<tt>true</tt> if <tt>(bits & flag)</tt> is non-zero.
     */
    public static boolean test(long flag, long bits) {
	return ((bits & flag) != 0);
    }

    /**
     * Creates a padded upper-case string representation of the integer
     * argument in base 16.
     *
     * @param	i	an integer.
     * @return	a padded upper-case string representation in base 16.
     */
    public static String toHexString(int i) {
	return toHexString(i, 8);
    }
    
    /**
     * Creates a padded upper-case string representation of the integer
     * argument in base 16, padding to at most the specified number of digits.
     *
     * @param	i	an integer.
     * @param	pad	the minimum number of hex digits to pad to.
     * @return	a padded upper-case string representation in base 16.
     */
    public static String toHexString(int i, int pad) {
	String result = Integer.toHexString(i).toUpperCase();
	while (result.length() < pad)
	    result = "0" + result;
	return result;
    }

    /**
     * Divide two non-negative integers, round the quotient up to the nearest
     * integer, and return it.
     *
     * @param	a	the numerator.
     * @param	b	the denominator.
     * @return	<tt>ceiling(a / b)</tt>.
     */
    public static int divRoundUp(int a, int b) {
	assertTrue(a >= 0 && b > 0);

	return ((a + (b-1)) / b);	
    }

    /**
     * Load and return the named class, or return <tt>null</tt> if the class
     * could not be loaded.
     *
     * @param	className	the name of the class to load.
     * @return	the loaded class, or <tt>null</tt> if an error occurred.
     */
    public static Class tryLoadClass(String className) {
	try {
	    return ClassLoader.getSystemClassLoader().loadClass(className);
	}
	catch (Throwable e) {
	    return null;
	}
    }	    

    /**
     * Load and return the named class, terminating Nachos on any error.
     *
     * @param	className	the name of the class to load.
     * @return	the loaded class.
     */
    public static Class loadClass(String className) {
	try {
	    return ClassLoader.getSystemClassLoader().loadClass(className);
	}
	catch (Throwable e) {
	    Machine.terminate(e);
	    return null;
	}
    }

    /**
     * Create and return a new instance of the named class, using the
     * constructor that takes no arguments.
     *
     * @param	className	the name of the class to instantiate.
     * @return	a new instance of the class.
     */
    public static Object constructObject(String className) {
	try {
	    // kamil - workaround for Java 1.4
	    // Thanks to Ka-Hing Cheung for the suggestion.
            // Fixed for Java 1.5 by geels
            Class[] param_types = new Class[0];
            Object[] params = new Object[0];
	    return loadClass(className).getConstructor(param_types).newInstance(params);
	}
	catch (Throwable e) {
	    Machine.terminate(e);
	    return null;
	}
    }

    /**
     * Verify that the specified class extends or implements the specified
     * superclass.
     *
     * @param	cls	the descendant class.
     * @param	superCls	the ancestor class.
     */
    public static void checkDerivation(Class<?> cls, Class<?> superCls) {
	Lib.assertTrue(superCls.isAssignableFrom(cls));
    }

    /**
     * Verifies that the specified class is public and not abstract, and that a
     * constructor with the specified signature exists and is public.
     *
     * @param	cls	the class containing the constructor.
     * @param	parameterTypes	the list of parameters.
     */
    public static void checkConstructor(Class cls, Class[] parameterTypes) {
	try {
	    Lib.assertTrue(Modifier.isPublic(cls.getModifiers()) &&
		       !Modifier.isAbstract(cls.getModifiers()));
	    Constructor constructor = cls.getConstructor(parameterTypes);
	    Lib.assertTrue(Modifier.isPublic(constructor.getModifiers()));
	}
	catch (Exception e) {
	    Lib.assertNotReached();
	}		       
    }

    /**
     * Verifies that the specified class is public, and that a non-static
     * method with the specified name and signature exists, is public, and
     * returns the specified type.
     *
     * @param	cls	the class containing the non-static method.
     * @param	methodName	the name of the non-static method.
     * @param	parameterTypes	the list of parameters.
     * @param	returnType	the required return type.
     */
    public static void checkMethod(Class cls, String methodName,
				   Class[] parameterTypes, Class returnType) {
	try {
	    Lib.assertTrue(Modifier.isPublic(cls.getModifiers()));
	    Method method = cls.getMethod(methodName, parameterTypes);
	    Lib.assertTrue(Modifier.isPublic(method.getModifiers()) &&
		       !Modifier.isStatic(method.getModifiers()));
	    Lib.assertTrue(method.getReturnType() == returnType);
	}
	catch (Exception e) {
	    Lib.assertNotReached();
	}		       
    }
    
    /**
     * Verifies that the specified class is public, and that a static method
     * with the specified name and signature exists, is public, and returns the
     * specified type.
     *
     * @param	cls	the class containing the static method.
     * @param	methodName	the name of the static method.
     * @param	parameterTypes	the list of parameters.
     * @param	returnType	the required return type.
     */
    public static void checkStaticMethod(Class cls, String methodName,
					 Class[] parameterTypes,
					 Class returnType) {
	try {
	    Lib.assertTrue(Modifier.isPublic(cls.getModifiers()));
	    Method method = cls.getMethod(methodName, parameterTypes);
	    Lib.assertTrue(Modifier.isPublic(method.getModifiers()) &&
		       Modifier.isStatic(method.getModifiers()));
	    Lib.assertTrue(method.getReturnType() == returnType);
	}
	catch (Exception e) {
	    Lib.assertNotReached();
	}		       
    }

    /**
     * Verifies that the specified class is public, and that a non-static field
     * with the specified name and type exists, is public, and is not final.
     *
     * @param	cls	the class containing the field.
     * @param	fieldName	the name of the field.
     * @param	fieldType	the required type.
     */
    public static void checkField(Class cls, String fieldName,
				  Class fieldType) {
	try {
	    Lib.assertTrue(Modifier.isPublic(cls.getModifiers()));
	    Field field = cls.getField(fieldName);
	    Lib.assertTrue(field.getType() == fieldType);
	    Lib.assertTrue(Modifier.isPublic(field.getModifiers()) &&
		       !Modifier.isStatic(field.getModifiers()) &&
		       !Modifier.isFinal(field.getModifiers()));
	}
	catch (Exception e) {
	    Lib.assertNotReached();
	}
    }

    /**
     * Verifies that the specified class is public, and that a static field
     * with the specified name and type exists and is public.
     *
     * @param	cls	the class containing the static field.
     * @param	fieldName	the name of the static field.
     * @param	fieldType	the required type.
     */
    public static void checkStaticField(Class cls, String fieldName,
					Class fieldType) {
	try {
	    Lib.assertTrue(Modifier.isPublic(cls.getModifiers()));
	    Field field = cls.getField(fieldName);
	    Lib.assertTrue(field.getType() == fieldType);
	    Lib.assertTrue(Modifier.isPublic(field.getModifiers()) &&
		       Modifier.isStatic(field.getModifiers()));
	}
	catch (Exception e) {
	    Lib.assertNotReached();
	}
    }
}