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[INFO] Bitsums and Operators


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ot_207
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Old 04-19-2009 , 04:20   [INFO] Bitsums and Operators
Reply With Quote #1

About:
This tutorial is meant for beginner scripters from amxx. This will teach you on how to use bitsum operators and show some advantages over boolean storage arrays!

What is a bitsum?
A bitsum is based on the way memory works. If we think, the memory chip containes cells (bits) that can hold 2 infos: 1 and 0. To store a number in one byte (byte = 8 bits) here is how to do it:
"8" (normal number) = "00001000" (memory number [1 byte])

How does a bitsum work?

Well the idea is that bitsums allow to control the position that we want to set it to 1. And we can check wether that position has 1 or 0.

What operators do I have, and what do they mean?
I will give an example for each operator:

PHP Code:
Operator: |
first_byte "10010001"
second_byte "01010001"

first_byte second_byte "11010001" 
So basically this operator works like the logical one || but it does the operation on each bit!

Code:
|     1      0
1     1      1
0     1      0
PHP Code:
Operator: &
first_byte "10010001"
second_byte "01010001"

first_byte second_byte "0001001" 
So basically this operator works like the logical one && but it does the operation on each bit!

Code:
&     1      0
1     1      0
0     0      0
PHP Code:
Operator: ^ (Exclusive OR)
first_byte "10010001"
second_byte "01010001"

first_byte second_byte "1100000" 
So basically this operator works like the logical one ^^ but it does the operation on each bit!

Code:
^    1      0
1    0      1
0    1      0
PHP Code:
Operator: ~ (Complement applies on only one number!)
first_byte "10010001"

~first_byte "01101110" 
So basically this operator negates every bit! So 0 becomes 1 and 1 becomes 0.

Code:
~1 = 0
~0 = 1
How do normal numbers work?
They are stored in the normal cells by base. So they are converted from base 10 from base 2. In this case number 9 for example becomse: "00001001". To comvert that number from the cells back to 9 we need to multiply each position with 2 and a power of it! 2^2 = power(2,2) = 4
00001001: 1*(2^0) + 0*(2^1) + 0*(2^2) + 1*(2^3) + 0*(2^4) + 0*(2^5) + 0*(2^6) + 0*(2^7) = 1 + 8 = 9

How can I easily create a bitsum?
Well you need 2 operators: << and >>, or if you don't want to use those operators you can easily create one by using elements that represent powers of 2.
Example:
PHP Code:
Bitsum "00001111" 
The 2 operators have a special meaning!
"<< x" means that a position of a number is moved by x points to left! Example:
PHP Code:
"00001100" << "00011000" 
When we convert this to normal number we can see that the normal number was multiplied by 2.
So if we have (1<<3) it would be like 2^3 * 1

The >> operator does the same thing like << but moves x points to right! When using integer variables the numbers disappear.
PHP Code:
"00000111" >> "00000000" 
So using those 2 operators to create a bitsum we have this:
PHP Code:
Bitsum "00001111" = (1<<1<<1<<1<<0
How can I use this in my scripts?
Well it can be used for insance instead of boolean arrays.

So instead of having this:
PHP Code:
new bool:is_alive[33
We have:
PHP Code:
new bitsum_is_alive 
So less memory usage!

Instead of
PHP Code:
if (is_alive[id])
{

We have:
PHP Code:
if (bistum_is_alive & (1<<id))
{

Instead of this
PHP Code:
is_alive[id] = true 
PHP Code:
is_alive[id] = false 
We will have this:
PHP Code:
bitsum_is_alive |= (1<<id
PHP Code:
bitsum_is_alive &=  ~(1<<id
The good thing is that you can extend the limit of the 32 slots that a simple number allowes with an array so that we can have more slots.
Ex:

PHP Code:
new holder[4]
// holder has 4 * 32 places where we can store the true/false value
// Here are the functions that allow you to manipulate them!

// Here we make the desired slot true
save(x)
{
    
holder[32] |= << (32);
}

// Here we check the desired slot 
exists(x)
{
    return 
holder[32] & << (32);
}
 
// Here we remove the desired slot 
remove(x)
{
    
holder[32] &= ~(<< (32))

As you can see it is harder to use bitsums but they have better results when it comes to low memory usage!
Hope that my english was fine!
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Last edited by ot_207; 05-20-2009 at 05:03.
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Old 04-19-2009 , 08:04   Re: [INFO] Bitsums and Operators
Reply With Quote #2

Wow thx for Great TUT!
Quote:
Originally Posted by ot_207 View Post
So less memory usage!
Profiled:

Code:
date: Sun Apr 19 15:20:28 2009 map: de_dust
type |                             name |      calls | time / min / max
-------------------------------------------------------------------
   n |                   register_clcmd |          2 | 0.000019 / 0.000004 / 0.000015
   p |                       array_test |         10 | 0.064196 / 0.006202 / 0.006642
   p |                      bitsum_test |         10 | 0.029594 / 0.002811 / 0.003570
   p |                      plugin_init |          1 | 0.000002 / 0.000002 / 0.000002
0 natives, 0 public callbacks, 3 function calls were not executed.

Tested on this code:
PHP Code:
#include <amxmodx>

new array[33]
new 
bitsum

public plugin_init() 
{
    array[
32] = false
        
    bitsum 
&=  ~(1<<32
    
    
register_clcmd("array","array_test")
    
register_clcmd("bitsum","bitsum_test")
}

public 
bitsum_test()
{
    for(new 
i;i<=1_000_000;i++)
        if(
bitsum & (1<<32))
            continue;
}

public 
array_test()
{
    for(new 
i;i<=1_000_000;i++)
        if(array[
32])
            continue;


Now I'm thinking should I swap arrays with bitsums in my plugins code. It would use less memory, but it will be harder to understand the code.

Last edited by Empowers; 04-19-2009 at 11:00.
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ot_207
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Old 04-19-2009 , 08:52   Re: [INFO] Bitsums and Operators
Reply With Quote #3

Thanks for profiling this and for having the patience to read it .
Indeed it will be harder to understand the code but you can also do some stocks that will make it easier to read .
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Last edited by ot_207; 04-19-2009 at 08:55.
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Old 04-19-2009 , 10:59   Re: [INFO] Bitsums and Operators
Reply With Quote #4

Quote:
Originally Posted by ot_207 View Post
you can also do some stocks that will make it easier to read .
Wow! Thats interesting.
Can you give an example of such a stock?
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ot_207
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Old 04-19-2009 , 11:17   Re: [INFO] Bitsums and Operators
Reply With Quote #5

Example:

PHP Code:
stock is_user_alive(id)
{
      return (
bistum_is_alive & (1<<id)) ? 0

Or macro:

PHP Code:
#define is_user_alive(%1) (bistum_is_alive & (1 << %1)) ? 1 : 0 
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Arkshine
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Join Date: Oct 2005
Old 04-19-2009 , 11:21   Re: [INFO] Bitsums and Operators
Reply With Quote #6

Macro is more appropriate here. Also you can do something that to return 0 or 1.

Code:
#define is_user_alive(%1) !!(bistum_is_alive & (1 << %1))
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joaquimandrade
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Old 04-19-2009 , 12:10   Re: [INFO] Bitsums and Operators
Reply With Quote #7

Quote:
Originally Posted by Empowers View Post
Wow thx for Great TUT!


Profiled:
Code:

Code:
date: Sun Apr 19 15:20:28 2009 map: de_dust
type |                             name |      calls | time / min / max
-------------------------------------------------------------------
   n |                   register_clcmd |          2 | 0.000019 / 0.000004 / 0.000015
   p |                       array_test |         10 | 0.064196 / 0.006202 / 0.006642
   p |                      bitsum_test |         10 | 0.029594 / 0.002811 / 0.003570
   p |                      plugin_init |          1 | 0.000002 / 0.000002 / 0.000002
0 natives, 0 public callbacks, 3 function calls were not executed.
Tested on this code:
PHP Code:
#include <amxmodx>new array[33]new bitsumpublic plugin_init() {    array[32] = false            bitsum &=  ~(1<<32)         register_clcmd("array","array_test")    register_clcmd("bitsum","bitsum_test")}public bitsum_test(){    for(new i;i<=1_000_000;i++)        if(bitsum & (1<<32))            continue;}public array_test(){    for(new i;i<=1_000_000;i++)        if(array[32])            continue;} 
Now I'm thinking should I swap arrays with bitsums in my plugins code. It would use less memory, but it will be harder to understand the code.
That profile is wrong.
PHP Code:
#include <amxmodx>

new array[3]
new 
bitsum

public Index(n)
{
    return array[
n]
}

public 
Bit(n)
{
    return (
bitsum & (1<<n))
}

public 
plugin_cfg()
{
    array[
1] = true
    bitsum   
= (<< 1
    
    for(new 
i;i<10000;i++)
    {
        
Bit(1)
        
Index(1);
        
Bit(2);
        
Index(2);
    }
    
    
server_cmd("quit");

HTML Code:
date: Sun Apr 19 08:56:46 2009 map: de_dust2
type |                             name |      calls | time / min / max
-------------------------------------------------------------------
   n |                       server_cmd |          1 | 0.000013 / 0.000013 / 0.000013
   p |                       plugin_cfg |          1 | 0.088612 / 0.088612 / 0.088612
   f |                              Bit |      20000 | 0.043302 / 0.000001 / 0.000040
   f |                            Index |      20000 | 0.043490 / 0.000001 / 0.000104
0 natives, 2 public callbacks, 1 function calls were not executed.

date: Sun Apr 19 08:57:13 2009 map: de_dust2
type |                             name |      calls | time / min / max
-------------------------------------------------------------------
   n |                       server_cmd |          1 | 0.000012 / 0.000012 / 0.000012
   p |                       plugin_cfg |          1 | 0.094011 / 0.094011 / 0.094011
   f |                              Bit |      20000 | 0.045281 / 0.000001 / 0.000012
   f |                            Index |      20000 | 0.046318 / 0.000001 / 0.000488
0 natives, 2 public callbacks, 1 function calls were not executed.

date: Sun Apr 19 08:57:20 2009 map: de_dust2
type |                             name |      calls | time / min / max
-------------------------------------------------------------------
   n |                       server_cmd |          1 | 0.000016 / 0.000016 / 0.000016
   p |                       plugin_cfg |          1 | 0.092532 / 0.092532 / 0.092532
   f |                              Bit |      20000 | 0.044500 / 0.000001 / 0.000023
   f |                            Index |      20000 | 0.044818 / 0.000001 / 0.000137
0 natives, 2 public callbacks, 1 function calls were not executed.

date: Sun Apr 19 08:57:28 2009 map: de_dust2
type |                             name |      calls | time / min / max
-------------------------------------------------------------------
   n |                       server_cmd |          1 | 0.000014 / 0.000014 / 0.000014
   p |                       plugin_cfg |          1 | 0.095900 / 0.095900 / 0.095900
   f |                              Bit |      20000 | 0.045795 / 0.000001 / 0.000194
   f |                            Index |      20000 | 0.045659 / 0.000001 / 0.000117
0 natives, 2 public callbacks, 1 function calls were not executed.
Bitsums can't be used to replace is_user_alive like you have it, because 1<<32 is out of the bits that a cell can hold.
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Old 04-19-2009 , 12:23   Re: [INFO] Bitsums and Operators
Reply With Quote #8

I don't know why it's wron..
I profiled your code here is the result:
Code:
date: Sun Apr 19 19:21:59 2009 map: de_dust
type |                             name |      calls | time / min / max
-------------------------------------------------------------------
   n |                       server_cmd |          1 | 0.000005 / 0.000005 / 0.000005
   p |                       plugin_cfg |          1 | 0.011147 / 0.011147 / 0.011147
   f |                            Index |      20000 | 0.006789 / 0.000000 / 0.000292
   f |                              Bit |      20000 | 0.005406 / 0.000000 / 0.000011
0 natives, 2 public callbacks, 1 function calls were not executed.
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joaquimandrade
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Old 04-19-2009 , 12:28   Re: [INFO] Bitsums and Operators
Reply With Quote #9

Quote:
Originally Posted by Empowers View Post
I don't know why it's wron..
I profiled your code here is the result:
Code:
date: Sun Apr 19 19:21:59 2009 map: de_dust
type |                             name |      calls | time / min / max
-------------------------------------------------------------------
   n |                       server_cmd |          1 | 0.000005 / 0.000005 / 0.000005
   p |                       plugin_cfg |          1 | 0.011147 / 0.011147 / 0.011147
   f |                            Index |      20000 | 0.006789 / 0.000000 / 0.000292
   f |                              Bit |      20000 | 0.005406 / 0.000000 / 0.000011
0 natives, 2 public callbacks, 1 function calls were not executed.
Your it's wrong because you are doing a continue instead of let the looping run. So you are calling 10 times the command and just giving 10 comparisons.
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ot_207
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Old 04-19-2009 , 12:51   Re: [INFO] Bitsums and Operators
Reply With Quote #10

Anyway it is not that different when it comes to cpu power usage. It helps when we talk about memory usage.
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