On 12/7/05, Vanlerberghe, Luc <[EMAIL PROTECTED]> wrote:
> Since 'byte' is signed in Java, can't the first test be simply written
> as
> if (b>0) return b;
> Doing an 'and' of two bytes and checking if the result is 0 probably
> requires masking operations on >8 bit processors...
Yep, that was my assumption and what I started off with actually.
Lo and behold, it was slower than the mask. I have no idea why.
> Also perhaps change to
> int b=readByte()) so that all operators use int's...
That was also my instinct... didn't pan out.
Below is the test program I used, as well as most of the variations
(some I just edited and are gone...). VInt2a was consistently fastest
of the variations. VInt1 is the original nad is fastest for all
single byte vints.
-Yonik
import java.io.IOException;
import java.util.Random;
/**
* @author yonik
*/
class VInt1 extends VInt {
public int readVInt() throws IOException {
byte b = readByte();
int i = b & 0x7F;
for (int shift = 7; (b & 0x80) != 0; shift += 7) {
b = readByte();
i |= (b & 0x7F) << shift;
}
return i;
}
}
class VInt2 extends VInt {
public int readVInt() throws IOException {
byte b = readByte();
if (b>=0) return b;
b &= 0x7f;
byte b2 = readByte();
if (b2>=0) return (b2<<7) | b;
b2 &= 0x7f;
byte b3 = readByte();
if (b3>=0) return (b3<<14) | (b2<<7) | b;
b3 &= 0x7f;
byte b4 = readByte();
if (b4>=0) return (b4<<21) | (b3<<14) | (b2<<7) | b;
b4 &= 0x7f;
byte b5 = readByte();
return (b5<<28) | (b4<<21) | (b3<<14) | (b2<<7) | b;
}
}
class VInt2a extends VInt {
public int readVInt() throws IOException {
byte b = readByte();
if ((b&0x80)==0) return b;
b &= 0x7f;
byte b2 = readByte();
if ((b&0x80)==0) return (b2<<7) | b;
b2 &= 0x7f;
byte b3 = readByte();
if ((b&0x80)==0) return (b3<<14) | (b2<<7) | b;
b3 &= 0x7f;
byte b4 = readByte();
if ((b&0x80)==0) return (b4<<21) | (b3<<14) | (b2<<7) | b;
b4 &= 0x7f;
byte b5 = readByte();
return (b5<<28) | (b4<<21) | (b3<<14) | (b2<<7) | b;
}
}
class VInt3 extends VInt {
public int readVInt() throws IOException {
int b = readByte();
if (b>=0) return b;
b &= 0x7f;
int b2 = readByte();
if (b2>=0) return (b2<<7) | b;
b2 &= 0x7f;
int b3 = readByte();
if (b3>=0) return (b3<<14) | (b2<<7) | b;
b3 &= 0x7f;
int b4 = readByte();
if (b4>=0) return (b4<<21) | (b3<<14) | (b2<<7) | b;
b4 &= 0x7f;
int b5 = readByte();
return (b5<<28) | (b4<<21) | (b3<<14) | (b2<<7) | b;
}
}
class VInt3a extends VInt {
public int readVInt() throws IOException {
int b = readByte();
if (b>=0) return b;
b &= 0x7f;
int b2 = readByte();
if (b2>=0) return (b2<<7) | b;
b2 &= 0x7f;
int b3 = readByte();
if (b3>=0) return (b3<<14) | (b2<<7) | b;
b3 &= 0x7f;
int b4 = readByte();
if (b4>=0) return (b4<<21) | (b3<<14) | (b2<<7) | b;
b4 &= 0x7f;
int b5 = readByte();
return (b5<<28) | (b4<<21) | (b3<<14) | (b2<<7) | b;
}
}
class VInt4 extends VInt {
public int readVInt() throws IOException {
byte b = readByte();
if (b>=0) return b;
byte b2 = readByte();
if (b2>=0) return (b2<<7) | (b&0x7f);
byte b3 = readByte();
if (b3>=0) return (b3<<14) | ((b2&0x7f)<<7) | (b&0x7f);
byte b4 = readByte();
if (b4>=0) return (b4<<21) | ((b3&0x7f)<<14) | ((b2&0x7f)<<7) | (b&0x7f);
byte b5 = readByte();
return (b5<<28) | ((b4&0x7f)<<21) | ((b3&0x7f)<<14) |
((b2&0x7f)<<7) | (b&0x7f);
}
}
class VInt5 extends VInt {
public int readVInt() throws IOException {
int i = readByte();
if (i>=0) return i;
i = (i & 0x7f) | (readByte() << 7);
if (i>=0) return i;
i = (i & (-1>>>(32-14))) | (readByte() << 14);
if (i>=0) return i;
i = (i & (-1>>>(32-21))) | (readByte() << 21);
if (i>=0) return i;
i = (i & (-1>>>(32-28))) | (readByte() << 28);
return i;
}
}
class VInt6 extends VInt {
public int readVInt() throws IOException {
byte b = readByte();
int i = b;
if (b>=0) return i;
i &= 0x7f;
b = readByte();
i |= (b & 0x7f)<<7;
if (b>=0) return i;
b = readByte();
i |= (b & 0x7f)<<14;
if (b>=0) return i;
b = readByte();
i |= (b & 0x7f)<<21;
if (b>=0) return i;
b = readByte();
i |= b<<28;
return i;
}
}
class VInt6a extends VInt {
public int readVInt() throws IOException {
byte b = readByte();
int i = b;
if ((b&0x80)==0) return i;
i &= 0x7f;
b = readByte();
i |= (b & 0x7f)<<7;
if ((b&0x80)==0) return i;
b = readByte();
i |= (b & 0x7f)<<14;
if ((b&0x80)==0) return i;
b = readByte();
i |= (b & 0x7f)<<21;
if ((b&0x80)==0) return i;
b = readByte();
i |= b<<28;
return i;
}
}
public class VInt {
byte[] arr = new byte[4096];
int pos = 0;
public void reset() { pos=0; }
public byte readByte() {
return arr[pos++];
}
public void writeByte(byte b) {
arr[pos++] = b;
}
public int readVInt() throws IOException {
return 0;
}
public void writeVInt(int i) throws IOException {
while ((i & ~0x7F) != 0) {
writeByte((byte)((i & 0x7f) | 0x80));
i >>>= 7;
}
writeByte((byte)i);
}
public static void main(String[] args) throws IOException,
ClassNotFoundException, IllegalAccessException, InstantiationException
{
String impl = args[0];
int maxnum= Integer.parseInt(args[1]); // maximum vint value
int iter = Integer.parseInt(args[2]);
VInt vint = new VInt1();
VInt test = (VInt)Class.forName(impl).newInstance();
Random rand = new Random(0);
while (vint.pos<vint.arr.length-5) {
int i = rand.nextInt(maxnum);
vint.writeVInt(i);
test.writeVInt(i);
}
int end = vint.pos+1;
test.reset(); vint.reset();
while (vint.pos<end) {
int i = vint.readVInt();
int i2 = test.readVInt();
if (i != i2) {
System.out.println("ERROR!!! " + Integer.toHexString(i) + ","
+ Integer.toHexString(i2));
}
}
int ret=0;
long start = System.currentTimeMillis();
for (int i=0; i<iter; i++) {
test.reset();
while (test.pos < end) {
ret += test.readVInt();
}
}
long stop = System.currentTimeMillis();
System.out.println("TIME="+(stop-start) + "\tret="+ret);
}
}
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