Thread: Bitwise operation; flag look up

Hi, I'm new here and am having trouble getting bitwise operations to work.

I have a typedef struct called typebs, I initialize the stuct variable as typebs bs.

I'm trying to read the first four bits (eventually the entire 28 bits in the field) using the following piece of code:

Code:

    bs.mouse = periphrials[0] & (1 << 0);
    bs.keyboard = periphrials[0] & (1 << 1);
    bs.gun = periphrials[0] & (1 << 2);
    bs.expand_analog_vert = periphrials[0] & (1 << 3);

The variables mouse, keyboard, gun and expand_analog_vert are all int types. The variable periphrials is a char array that holds a hex number -- in my current case this number is E019010.

What I'm expecting is either a 1 or 0 (on or off) put into the int variables, what I'm getting is 1, 0, 4, 0.

What am I missing and how can I properly implement this?

Does too work!

Code:

#include <stdio.h>

int main(){

    int a = 0xE019019;

    printf("%i%i%i%i\n",(a & 8)!=0, (a & 4)!= 0, (a & 2)!= 0, (a & 1)!= 0);


    return 0;
}

I made a small change to your number though because the "nibble" was all zeros. This prints the individual bits from the least significant nibble.

Originally Posted by emptythought

Hi, I'm new here and am having trouble getting bitwise operations to work.

I have a typedef struct called typebs, I initialize the stuct variable as typebs bs.

I'm trying to read the first four bits (eventually the entire 28 bits in the field) using the following piece of code:

Code:

    bs.mouse = periphrials[0] & (1 << 0);
    bs.keyboard = periphrials[0] & (1 << 1);
    bs.gun = periphrials[0] & (1 << 2);
    bs.expand_analog_vert = periphrials[0] & (1 << 3);

The variables mouse, keyboard, gun and expand_analog_vert are all int types. The variable periphrials is a char array that holds a hex number -- in my current case this number is E019010.

What I'm expecting is either a 1 or 0 (on or off) put into the int variables, what I'm getting is 1, 0, 4, 0.

What am I missing and how can I properly implement this?

What is the type of your periphrials[ ]?

Looking at your source material at the link given, it appears that the mouse bit is the most significant bit in the 28bit field. This is definitely not the (1<<0) bit. What it should be depends on the type of periphrials[ ]. Instead of an array, if perihrials was a 32-bit quantity (unsigned long in some implementations), the mouse bit would either be (1<<31) or (1<<27) depending on where the 28 bits were positioned in the 32 bit field.

Originally Posted by Syscal

Does too work!

...

I made a small change to your number though because the "nibble" was all zeros. This prints the individual bits from the least significant nibble.

As I mentioned below the peripherals (thanks spell check for the typo!) variable is type character. How can I convert that hex digit into say, an unsigned long when sscanf_s is only available to Windows?

Originally Posted by Syscal

Code:

int check(int *arg, int FLAG){
    return (*arg & FLAG) != 0;
}

Here's an example I just finished that shows the first issue your code gave me.

Code:

#include <stdio.h>

int check(int *arg, int FLAG)	{
    return(*arg & FLAG) != 0;
}

int main(void)	{
    char a[] = "B000010";

    printf("%i%i%i%i\n", check(a, 0x1), check(a, 0x2), check(a, 0x4),
          check(a, 0x8));

    return 0 ;
}

mouse, keyboard and expand_ananlog_vert are set and it reports 0100.

Originally Posted by pheininger

What is the type of your periphrials[ ]?

Looking at your source material at the link given, it appears that the mouse bit is the most significant bit in the 28bit field. This is definitely not the (1<<0) bit. What it should be depends on the type of periphrials[ ]. Instead of an array, if perihrials was a 32-bit quantity (unsigned long in some implementations), the mouse bit would either be (1<<31) or (1<<27) depending on where the 28 bits were positioned in the 32 bit field.

It is a character with 8 elements.

main.c\cpp - C | #include <stdio.h> #include - Etdcdev - gzJhpnh6 - Pastebin.com
main.h - C | #define MR_MAX_COLORS 127 # - Etdcdev - XgZr9uLr - Pastebin.com

Thanks.

I did. It just returns 0010...

Originally Posted by Syscal

...

I made a small change to your number though because the "nibble" was all zeros. This prints the individual bits from the least significant nibble.

Reading over this again; I don't get what you meant by this? I noticed the change; how would a change from a 0 to a 9 change the way the individual bits are printed?

Originally Posted by Syscal

You want this to be interpreted as hex right? Why cant you just use an int?

How can I convert that hex digit into say, an unsigned long when sscanf_s is only available to Windows?

Given this from your linked page ...

Code:

<A><-------B------> <C->
0000 0000 0000 0000 0000 0000 0000
^^^^ ^^^^ ^^^^ ^^^^ ^^^^    ^    ^
|||| |||| |||| |||| ||||    |    |
|||| |||| |||| |||| ||||    |    +----- Uses Windows CE
|||| |||| |||| |||| ||||    |
|||| |||| |||| |||| ||||    +-----  VGA box support
|||| |||| |||| |||| ||||
|||| |||| |||| |||| |||+----- Other expansions
|||| |||| |||| |||| ||+----- Puru Puru pack
|||| |||| |||| |||| |+----- Mike device
|||| |||| |||| |||| +----- Memory card
|||| |||| |||| |||+------ Start + A + B + Directions
|||| |||| |||| ||+------ C button
|||| |||| |||| |+------ D button
|||| |||| |||| +------ X button
|||| |||| |||+------- Y button
|||| |||| ||+------- Z button
|||| |||| |+------- Expanded direction buttons
|||| |||| +------- Analog R trigger
|||| |||+-------- Analog L trigger
|||| ||+-------- Analog horizontal controller
|||| |+-------- Analog vertical controller
|||| +-------- Expanded analog horizontal
|||+--------- Expanded analog vertical
||+--------- Gun
|+--------- Keyboard
+--------- Mouse

This is roughage just to give an idea... it is 100% untested...

Code:

 
typedef union tBits
   { unsigned long  Peripherals;
      unsigned long Other : 1,
                              Puru  : 1,
                              Mike  : 1,
                              Card  : 1,
                              SAB   : 1,
                              Cbtn  : 1,
                              Dbtn  : 1,
                              Xbtn  : 1,
                              Ybtn  : 1,
                              Zbtn  : 1, 
                              EBtn  : 1,
                              ART    : 1,
                              ALT    : 1 ,
                              AHC   : 1,
                              AVC   : 1,
                              EAH   : 1,
                              EAV   : 1,
                              Gun  : 1,
                              Kbd  : 1,
                              Mse  : 1; }  BITS, *pBITS;

BITS  bs;

BS.Peripherals = Peripherals[0];

If (bs.Kbd)
  puts("Well lookie there");

The union should allow you to write in a DWord and read it as bits...

I agree bitfields operating on externally defined values can be a bit dodgy and appreciate the warnings given... but, in my own defense I did say I was just thinking out loud...