Contents

• About the operation counting methodology
• Compute the sign of an integer
• 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
  • Sign extending from a constant bit width
  • Sign extending from a variable bit-width
  • Sign extending from a variable bit-width in 3 operations
• Conditionally set or clear bits without branching
• Merge bits from two values according to a mask
• Counting bits set
  • Counting bits set, naive way
  • Counting bits set by lookup table
  • Counting bits set, Brian Kernighan’s way
  • Counting bits set in 12, 24, or 32-bit words using 64-bit instructions
  • Counting bits set, in parallel
• Computing parity (1 if an odd number of bits set, 0 otherwise)
  • Compute parity of a word the naive way
  • Compute parity by lookup table
  • Compute parity of a byte using 64-bit multiply and modulus division
  • Compute parity in parallel
• Swapping Values
  • Swapping values with XOR
  • Swapping individual bits with XOR
• Reversing bit sequences
  • Reverse bits the obvious way
  • Reverse bits in word by lookup table
  • Reverse the bits in a byte with 3 operations (64-bit muliply and modulus division)
  • Reverse the bits in a byte with 4 operations (64-bit multiply, no division)
  • Reverse the bits in a byte with 7 operations (no 64-bit, only 32)
  • Reverse an N-bit quantity in parallel with 5 * lg(N) operations
• Modulus division (aka computing remainders)
  • Computing modulus division by 1 << s without a division operation (obvious)
  • Computing modulus division by (1 << s) - 1 without a division operation
  • Computing modulus division by (1 << s) - 1 in parallel without a division operation
• Finding integer log base 2 of an integer (aka the position of the highest bit set)
  • Find the log base 2 of an integer with the MSB N set in O(N) operations (the obvious way)
  • Find the integer log base 2 of an integer with an 64-bit IEEE float
  • Find the log base 2 of an integer with a lookup table
  • Find the log base 2 of an N-bit integer in O(lg(N)) operations
  • Find the log base 2 of an N-bit integer in O(lg(N)) operations with multiply and lookup
• Find 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)
  • Count the consecutive zero bits (trailing) on the right in parallel
  • Count the consecutive zero bits (trailing) on the right by binary search
  • Count the consecutive zero bits (trailing) on the right by casting to a float
  • Count the consecutive zero bits (trailing) on the right with modulus division and lookup
  • Count the consecutive zero bits (trailing) on the right with multiply and lookup
• 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)
  • Interleave bits the obvious way
  • Interleave bits by table lookup
  • Interleave bits with 64-bit multiply
  • Interleave bits by Binary Magic Numbers
• Testing for ranges of bytes in a word (and counting occurances found)
• Determine if a word has a zero byte
• Determine if a word has byte less than n
• Determine if a word has a byte greater than n
• Determine if a word has a byte between m and n

[tags]bit manipulation,byte manipulation, bit manipulation source code, bit manipulation programs[/tags]