Bit Twiddling Hacks

• Computing the sign of an integer
• Detect if two integers have opposite signs
• Compute the integer absolute value (abs) without branching
• Compute the minimum (min) or maximum (max) of two integers without branching
• Determining if an integer is a power of 2
• Sign Extending
• Conditionally set or clear bits without branching
• Conditionally negate a value without branching
• Merge bits from two values according to a mask
• Counting bits set
• Computing parity (1 if an odd number of bits set, 0 otherwise)
• Swapping Values
• Reversing bit sequences
• Modulus division (aka computing remainders)
• Finding integer log base 2 of an integer (aka the position of the highest bit set)
• Finding integer log base 10 of an integer
• Find integer log base 2 of a 32-bit IEEE float
• Find integer log base 2 of the pow(2, r)-root of a 32-bit IEEE float (for unsigned integer r)
• Counting consecutive trailing zero bits (or finding bit indices)
• Round up to the next highest power of 2 by float casting
• Round up to the next highest power of 2
• Interleaving bits (aka computing Morton Numbers)
• Testing for ranges of bytes in a word (and counting occurances found)
• Compute the lexicographically next bit permutation
• log2f approximation