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Easier bitwise operations

, 25 Dec 2001 CPOL 129.3K 711 41
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A collection of templates that simplify the comprehension of bitwise operations
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Introduction

I've been developing software using C/C++ for a very long time yet I still have to think twice when I encounter bitwise operations, let alone when I have to explain them to somebody else! For example:

    unsigned const STAT_ONE = 0x0001;
    unsigned const STAT_TWO = 0x0002;
    
    unsigned status = 0x0001;
    if(status & (STAT_ONE | STAT_TWO)) // Does this evaluate to true or false?
       DoSomething();

We all know that the preceding statement checks if both STAT_ONE and STAT_TWO bits are set then DoSomething() will be executed... or is it if either STAT_ONE or STAT_TWO bits are set? Lets see:

    0001 or   // STAT_ONE
    0010      // STAT_TWO
    ----
    0011 and  // STAT_ONE | STAT_TWO
    0001      // status
    ----
    0001      // status & (STAT_ONE | STAT_TWO)

Because the result is non-zero then DoSomething() will be executed. I think this can be very tricky, especially if the expressions get too complex. Isn't the intent of the following code easier to understand and less error-prone?

    unsigned const STAT_ONE = 0x0001;
    unsigned const STAT_TWO = 0x0002;

    unsigned status = 0x0001;
    if(isAnyBitSet(status, STAT_ONE | STAT_TWO)) // This evaluates to true, bit
                                                 // STAT_ONE is set and bit STAT_TWO 
                                                 // isn't. Same as previous example
       DoSomething();
    if(areAllBitsSet(status, STAT_ONE | STAT_TWO)) // This evaluates to false, 
                                                   // bit STAT_ONE is set but bit 
                                                   // STAT_TWO isn't
       DoSomething();

Also it's very convenient to access a bit's value by its position like this:

    if(isBitSetByPos(status, 5))   
       bitClearByPos(status, 5);

All the functions provided in the BitTools.h header are inlined so there is no size or run-time speed tradeoffs to worry about.

Templates

Bitmask-based functions

  • template <class T, class U>
    bool isAnyBitSet(T value, U mask)

    Returns true if any of the bits in mask is set in value. Defined as: (value & mask) != 0
       1010 and  // value
       0110      // mask
       ----
       0010      // Non-zero: true
  • template <class T, class U>
    bool areAllBitsSet(T value, U mask)

    Returns true if all the bits in mask are set in value. Defined as: (value & mask) == mask
       1010 and  // value
       1110      // mask
       ----
       1010      // 1010 == 1010: true
  • template <class T, class U>
    bool areAllBitsClear(T value, U mask)

    Returns true if all the bits in mask are cleared in value. Defined as: (value & mask) == 0
       1010 and  // value
       0101      // mask
       ----
       0000      // Zero: true
  • template <class T, class U>
    T setBits(T value, U mask)

    Returns value with the mask bits set. Defined as: value | mask
       1000 or   // value
       0110      // mask
       ----
       1110
  • template <class T, class U>
    T setBitsExcept(T value, U mask)

    Returns value with the all the bits set except the mask bits. Defined as: value | ~mask
       1001 not  // mask
       ----
       0110 or   // ~mask
       0001      // value
       ----
       0111
  • template <class T, class U>
    T clearBits(T value, U mask)

    Returns value with the mask bits cleared. Defined as: value & ~mask
       1001 not  // mask
       ----
       0110 and  // ~mask
       1111      // value
       ----
       0110
  • template <class T, class U>
    T clearBitsExcept(T value, U mask)

    Returns value with the all the bits cleared except the mask bits. Defined as: value & mask
       0010 and  // value
       0110      // mask
       ----
       0010
  • template <class T, class U>
    T setClearBits(T value, U add, U remove)

    Returns value with the add bits set and the remove bits cleared. Defined as: (value | add) & ~remove
       1101 or   // value
       0101      // add
       ----
       0111
    
       0001 not  // remove
       ---- 
       1110 and  // ~remove
       0111      // value | add
       ----
       0110
  • template <class T, class U, class V>
    T setBits(T value, U mask, V set)

    Returns value with the mask bits set or cleared depending on the value of set.

Position-based functions

  • template <class T>
    T setBitByPos(T value, unsigned char n)

    Returns value with the nth bit set. Defined as value | (1 << n)

  • template <class T>
    T clearBitByPos(T value, unsigned char n)

    Returns value with the nth bit cleared. Defined as value & ~(1 << n)

  • template <class T>
    bool isBitSetByPos(T value, unsigned char n)

    Returns true if value has the the nth bit set. Defined as (value & (1 << n)) != 0

  • template <class T>
    bool isBitClearByPos(T value, unsigned char n)

    Returns true if value has the the nth bit cleared. Defined as (value & (1 << n)) == 0

Conclusion

The templates contained in BitTools.h provide an easier and less error-prone way of expressing bitwise operations with no performance or size penalties compared to hand written code. I hope you find these functions as useful and easy to use as I did.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Eddie Velasquez
Software Developer (Senior)
United States United States
No Biography provided

Comments and Discussions

 
GeneralNone Pin
Jonathan de Halleux25-Feb-03 21:49
memberJonathan de Halleux25-Feb-03 21:49 
GeneralWhy templates Pin
Bill Semaphore3-Jan-02 10:37
memberBill Semaphore3-Jan-02 10:37 
GeneralRe: Why templates Pin
Nemanja Trifunovic3-Jan-02 11:12
memberNemanja Trifunovic3-Jan-02 11:12 
GeneralRe: Why templates Pin
Eddie Velasquez3-Jan-02 14:52
memberEddie Velasquez3-Jan-02 14:52 
GeneralASSERTs Pin
Mike Klimentiev2-Jan-02 10:20
memberMike Klimentiev2-Jan-02 10:20 
GeneralRe: ASSERTs Pin
Eddie Velasquez3-Jan-02 2:36
memberEddie Velasquez3-Jan-02 2:36 
GeneralRe: ASSERTs Pin
Mike Klimentiev3-Jan-02 8:06
memberMike Klimentiev3-Jan-02 8:06 
GeneralRe: ASSERTs Pin
Eddie Velasquez4-Jan-02 2:23
memberEddie Velasquez4-Jan-02 2:23 
GeneralRe: ASSERTs Pin
Mike Klimentiev4-Jan-02 8:41
memberMike Klimentiev4-Jan-02 8:41 
GeneralRe: ASSERTs Pin
Eddie Velasquez4-Jan-02 8:53
memberEddie Velasquez4-Jan-02 8:53 
GeneralStandard C MACRO version Pin
Daniel May26-Dec-01 16:27
memberDaniel May26-Dec-01 16:27 
GeneralRe: Standard C MACRO version Pin
Eddie Velasquez27-Dec-01 3:19
memberEddie Velasquez27-Dec-01 3:19 
GeneralRe: Standard C MACRO version Pin
Daniel May27-Dec-01 3:23
memberDaniel May27-Dec-01 3:23 
GeneralRe: Standard C MACRO version Pin
Eddie Velasquez27-Dec-01 4:11
memberEddie Velasquez27-Dec-01 4:11 
GeneralI think this is much more intuitive. Pin
Henry Jacobs22-Dec-01 3:01
memberHenry Jacobs22-Dec-01 3:01 
GeneralI think this is less error prone Pin
okigan21-Dec-01 14:59
memberokigan21-Dec-01 14:59 
GeneralRe: I think this is less error prone Pin
Eddie Velasquez21-Dec-01 15:13
memberEddie Velasquez21-Dec-01 15:13 
GeneralRe: I think this is less error prone Pin
Philippe Lhoste2-Jan-02 23:28
memberPhilippe Lhoste2-Jan-02 23:28 
GeneralRe: I think this is less error prone Pin
Eddie Velasquez3-Jan-02 2:40
memberEddie Velasquez3-Jan-02 2:40 
GeneralRe: I think this is less error prone Pin
Philippe Lhoste3-Jan-02 3:21
memberPhilippe Lhoste3-Jan-02 3:21 
GeneralRe: I think this is less error prone Pin
okigan3-Jan-02 5:33
memberokigan3-Jan-02 5:33 
GeneralRe: I think this is less error prone Pin
Eddie Velasquez3-Jan-02 7:14
memberEddie Velasquez3-Jan-02 7:14 

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