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    <p>If you're doing a lot of bit twiddling you might want to use masks which will make the whole thing quicker. The following functions are very fast and are still flexible (they allow bit twiddling in bit maps of any size).</p> <pre><code>const unsigned char TQuickByteMask[8] = { 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, }; /** Set bit in any sized bit mask. * * @return none * * @param bit - Bit number. * @param bitmap - Pointer to bitmap. */ void TSetBit( short bit, unsigned char *bitmap) { short n, x; x = bit / 8; // Index to byte. n = bit % 8; // Specific bit in byte. bitmap[x] |= TQuickByteMask[n]; // Set bit. } /** Reset bit in any sized mask. * * @return None * * @param bit - Bit number. * @param bitmap - Pointer to bitmap. */ void TResetBit( short bit, unsigned char *bitmap) { short n, x; x = bit / 8; // Index to byte. n = bit % 8; // Specific bit in byte. bitmap[x] &amp;= (~TQuickByteMask[n]); // Reset bit. } /** Toggle bit in any sized bit mask. * * @return none * * @param bit - Bit number. * @param bitmap - Pointer to bitmap. */ void TToggleBit( short bit, unsigned char *bitmap) { short n, x; x = bit / 8; // Index to byte. n = bit % 8; // Specific bit in byte. bitmap[x] ^= TQuickByteMask[n]; // Toggle bit. } /** Checks specified bit. * * @return 1 if bit set else 0. * * @param bit - Bit number. * @param bitmap - Pointer to bitmap. */ short TIsBitSet( short bit, const unsigned char *bitmap) { short n, x; x = bit / 8; // Index to byte. n = bit % 8; // Specific bit in byte. // Test bit (logigal AND). if (bitmap[x] &amp; TQuickByteMask[n]) return 1; return 0; } /** Checks specified bit. * * @return 1 if bit reset else 0. * * @param bit - Bit number. * @param bitmap - Pointer to bitmap. */ short TIsBitReset( short bit, const unsigned char *bitmap) { return TIsBitSet(bit, bitmap) ^ 1; } /** Count number of bits set in a bitmap. * * @return Number of bits set. * * @param bitmap - Pointer to bitmap. * @param size - Bitmap size (in bits). * * @note Not very efficient in terms of execution speed. If you are doing * some computationally intense stuff you may need a more complex * implementation which would be faster (especially for big bitmaps). * See (http://graphics.stanford.edu/~seander/bithacks.html). */ int TCountBits( const unsigned char *bitmap, int size) { int i, count = 0; for (i=0; i&lt;size; i++) if (TIsBitSet(i, bitmap)) count++; return count; } </code></pre> <p>Note, to set bit 'n' in a 16 bit integer you do the following:</p> <pre><code>TSetBit( n, &amp;my_int); </code></pre> <p>It's up to you to ensure that the bit number is within the range of the bit map that you pass. Note that for little endian processors that bytes, words, dwords, qwords, etc., map correctly to each other in memory (main reason that little endian processors are 'better' than big-endian processors, ah, I feel a flame war coming on...).</p>
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    1. POHow do you set, clear, and toggle a single bit?
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    1. CODon't use a table for a function that can be implemented with a single operator. TQuickByteMask[n] is equivalent to (1<<n). Also, making your arguments short is a very bad idea. The / and % will actually be a division, not bitshift/bitwise and, because signed division by a power of 2 cannot be implemented bitwise. You should make the argument type unsigned int!
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    2. COWhat's the point with this? It only makes the code slower and harder to read? I can't see a single advantage with it. 1u << n is easier to read for C programmers, and can hopefully be translated into a single clock tick CPU instruction. Your division on the other hand, will be translated to something around 10 ticks, or even as bad as up to 100 ticks, depending on how poorly the specific architecture handles division. As for the bitmap feature, it would make more sense to have a lookup table translating each bit index to a byte index, to optimize for speed.
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    3. COAs for big/little endian, big endian will map integers and raw data (for example strings) in the same way: left-to-right msb to lsb throughout the whole bitmap. While little endian will map integers left to right as 7-0, 15-8, 23-18, 31-24, but raw data is still left-to-right msb to lsb. So how little endian is better for your particular algorithm is completely beyond me, it seems to be the opposite.
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