What is libbittwiddle

Libbittwiddle is a collection of bit manipulation routines.

The included routines are as follows:

• popcnt

  Computes set bits. Uses a compiler intrinsic if available. Results in 12 arithmetic operations, no branches.

• clz

  Computes leading zeros. Uses a compiler intrinsic if available. Results in 23-25 arithmetic operations, no branches.

• ctz

  Computes trailing zeros. Uses a compiler intrinsic if available. Results in 16 arithmetic operations, no branches.

• check_has_byte_eq

  Checks whether a number has a byte with a value equal to a value x. Results in 5 arithmetic operations, no branches.

• check_has_byte_lt

  Checks whether a number has a byte with a value less than a value x. It's possible to select from two implementations with the following performance characteristics: 4-5 arithmetic operations and a branch (default). 14-15 arithmetic operations and no branches.

  If the value x is known at compile-time, both implementations are equivalent and result in 4-5 arithmetic operations and no branches.

  The branchless implementation can be selected by defining LIBBITTWIDDLE_BRANCHLESS_CHECK_HAS_LTGT before including libbittwiddle.h

• check_has_byte_gt

  Checks whether a number has a byte with a value greater than a value x. It's possible to select from two implementations with the following performance characteristics: 3-4 arithmetic operations and a branch (default). 14-15 arithmetic operations and no branches.

  If the value x is known at compile-time, both implementations are equivalent and result in 3-4 arithmetic operations and no branches.

  The branchless implementation can be selected by defining LIBBITTWIDDLE_BRANCHLESS_CHECK_HAS_LTGT before including libbittwiddle.h

• check_has_byte_between

  Checks whether a number has a byte with a value between compile-time values x and y. Results in 7 arithmetic operations and no branches (the range of x and y is restricted).

A C++11-aware compiler is required.