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)) 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? Let's see:
0001 or 0010 
0011 and 0001 
0001
Because the result is nonzero, 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 errorprone?
unsigned const STAT_ONE = 0x0001;
unsigned const STAT_TWO = 0x0002;
unsigned status = 0x0001;
if(isAnyBitSet(status, STAT_ONE  STAT_TWO)) DoSomething();
if(areAllBitsSet(status, STAT_ONE  STAT_TWO)) 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 runtime speed tradeoffs to worry about.
Templates
Bitmaskbased 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 0110 
0010

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 1110 
1010

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 0101 
0000

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

template <class T, class U>
T setBitsExcept(T value, U mask)
Returns value
with all the bits set except the mask
bits. Defined as: value  ~mask
1001 not 
0110 or 0001 
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 
0110 and 1111 
0110

template <class T, class U>
T clearBitsExcept(T value, U mask)
Returns value
with all the bits cleared except the mask
bits. Defined as: value & mask
0010 and 0110 
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 0101 
0111
0001 not 
1110 and 0111 
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
.
Positionbased Functions

template <class T>
T setBitByPos(T value, unsigned char n)
Returns value
with the n
th bit set. Defined as value  (1 << n)

template <class T>
T clearBitByPos(T value, unsigned char n)
Returns value
with the n
th bit cleared. Defined as value & ~(1 << n)

template <class T>
bool isBitSetByPos(T value, unsigned char n)
Returns true
if value
has the n
^{th} bit set. Defined as (value & (1 << n)) != 0

template <class T>
bool isBitClearByPos(T value, unsigned char n)
Returns true
if value
has the n
^{th} bit cleared. Defined as (value & (1 << n)) == 0
Conclusion
The templates contained in BitTools.h provide an easier and less errorprone 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.
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