/prog/ - Bitwise operation

Name: Anonymous 2010-06-09 5:28

How are simple operations like adding and subtraction represented using only bitwise operators such as &, |, ^, >>, ~, and <<?

Also, do each of the bitwise operators perform at the same rate, or are some faster than others?

Name: Anonymous 2010-06-09 16:36

>>40
That's not actually better than the one or two idiots hating on Xarn because they're jealous of the attention he gets (or because they think their imageboard culture can be transplanted onto world4ch).

Name: Anonymous 2010-06-09 16:38

>>41
Are you Xarn? I thought so.

Name: Anonymous 2010-06-09 16:58

>>1
>>,
FUCKINGLY AMAZING

Name: Anonymous 2010-06-09 17:18

>>36
What's a compiler?

Name: Anonymous 2010-06-09 17:22

>>34
what the hell is that?

Name: Anonymous 2010-06-09 17:26

>>20
Did you mean:
[code]int add(int a, int b) {
if (!a) return b;
return add((a & b) << 1, a ^ b);
}

Name: Anonymous 2010-06-09 17:30

So I have found out a few things via googling
assume two unsigned integers a and b:[o]
a + b = ( ( a & b ) << 1 ) + ( a XOR b )[\o]

also

if ( a NAND b ) then ( a + b ) = a XOR b[o]
this is just saying if you don't have to carry while doing binary addition, then a + b is equal to a xor b [o][\o][\o]

So I was thinking about the a + b = a xor b part and realized there must be some way to extrapolate a + b to a sum of terms that where we can then apply the a xor b thing.

Any ideas?

Name: Anonymous 2010-06-09 18:01

assume a and b are the same size and are a list of bits
def a+b:
if size = 1: return (a&b, a^b)
else: return (first(a) + first(b) + first(rest(a)+rest(b)), rest(rest(a)+rest(b)))

Name: Anonymous 2010-06-09 18:49

z = ((x * 0x0101010101010101ULL & 0x8040201008040201ULL) * 

     0x0102040810204081ULL >> 49) & 0x5555 |

    ((y * 0x0101010101010101ULL & 0x8040201008040201ULL) * 

     0x0102040810204081ULL >> 48) & 0xAAAA;

Used this snippet a couple days ago, if you know what it does from just looking at it then you know what you doing.

Name: Anonymous 2010-06-09 19:14

>>49
It uses a bunch of meaningless magic numbers just to interpolate the bits of the result of some transformation of x and y as a short.

Name: Anonymous 2010-06-09 19:20

>>50++

Name: >> !!50++bKT00Wlp00p 2010-06-10 0:58

Name: Anonymous 2010-06-10 4:23

>>50
They aren't meaningless !!

Name: Anonymous 2010-06-10 12:07

>>49,53
Arithmetically interleaving bits!! I don't care!!

Name: Anonymous 2010-06-11 15:17

No need to ask,
He's a smooth operator

Name: Anonymous 2010-06-11 16:40

if (isSmoothOperator()) {

    throw new ParadoxException();

}

Name: Anonymous 2010-06-11 18:27

TOPICS IN ANALYSIS SMOOTH OPERATOR ALGEBRAS AND K-THEORY

Name: Anonymous 2010-06-17 19:44

interesting problem you came across

#include <stdio.h>



int main()

{

    int a,b,q=64;



    for (a=0; a<q; a++) {

        for (b=0; b<q; b++) {

            if ((a + b) == (a ^ b))

                printf("# ");

            else

                printf("  ");

        }

    printf("\n");

    }

    return 0;

}

# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #

Name: Anonymous 2010-06-17 19:46

#include <stdio.h>



int main()

{

    int a,b,q=64;



    for (a=0; a<q; a++) {

        for (b=0; b<q; b++) {

            if ((a + b) == ((a & b) << 1 ^ (a ^ b)))

                printf("# ");

            else

                printf("  ");

        }

    printf("\n");

    }

    return 0;

}

# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #

Name: Anonymous 2010-06-17 19:52

>>58 represents the efficiency of the XOR (and OR too) operator as a substitute for the addition operator. It looks like a Sierpinski triangle.

Name: Anonymous 2010-06-17 20:43



uintmax_t plus(uintmax_t a, uintmax_t b)

{ return a && b ? plus(a ^ b, (a & b) << 1) : a | b; }

Name: Anonymous 2010-06-18 0:04

Subtract:



int Sub (int X, int x)

{

    return (((~X & x) << 1) ?

      Sub((~(~X & ~x) & ~(X & x)),((~X & x) << 1)) :

        (~(~X & ~x) & ~(X & x)));

}

Name: Anonymous 2010-06-18 1:13

#include <stdio.h>

int main()
{
    int a,b,q=64;
    float c = 0.0;

    fgetc(stdin);

    for (a=0; a<q; a++) {
      c = a/2;
      while (c > 0) {
      printf(" ");
      c--;
      }
      for (b=0; b<q; b++) {
      if ((a + b) == (a ^ b))
      printf("# ");
      else
      printf(" ");
      }
    printf("\n");
    }
    return 0;
}

Name: Anonymous 2010-12-21 18:58

Name: Anonymous 2011-01-31 20:38

<-- check em dubz

Bitwise operation

1 Name: Anonymous 2010-06-09 5:28

41 Name: Anonymous 2010-06-09 16:36

42 Name: Anonymous 2010-06-09 16:38

43 Name: Anonymous 2010-06-09 16:58

44 Name: Anonymous 2010-06-09 17:18

45 Name: Anonymous 2010-06-09 17:22

46 Name: Anonymous 2010-06-09 17:26

47 Name: Anonymous 2010-06-09 17:30

48 Name: Anonymous 2010-06-09 18:01

49 Name: Anonymous 2010-06-09 18:49

50 Name: Anonymous 2010-06-09 19:14

51 Name: Anonymous 2010-06-09 19:20

52 Name: >> !!50++bKT00Wlp00p 2010-06-10 0:58

53 Name: Anonymous 2010-06-10 4:23

54 Name: Anonymous 2010-06-10 12:07

55 Name: Anonymous 2010-06-11 15:17

56 Name: Anonymous 2010-06-11 16:40

57 Name: Anonymous 2010-06-11 18:27

58 Name: Anonymous 2010-06-17 19:44

59 Name: Anonymous 2010-06-17 19:46

60 Name: Anonymous 2010-06-17 19:52

61 Name: Anonymous 2010-06-17 20:43

62 Name: Anonymous 2010-06-18 0:04

63 Name: Anonymous 2010-06-18 1:13

65 Name: Anonymous 2010-12-21 18:58

66 Name: Anonymous 2011-01-31 20:38