BMI2

BMI2, short for Bit Manipulation Instruction Set 2, is an extension to the x86-64 instruction set architecture that provides additional instructions for manipulating bits and bitfields. The extension was designed to enable faster implementations of routines that work with binary data, such as bit-field extraction, packing and unpacking, multi-precision arithmetic, and certain cryptographic operations. It follows BMI1 as part of the broader effort to accelerate low-level data handling on modern processors.

Availability and hardware support: BMI2 was introduced by Intel with the Haswell generation and later adopted by AMD in subsequent microarchitectures. Most modern desktop, mobile, and server CPUs from Intel and AMD support BMI2, making software-implemented bit manipulation faster on current hardware. The presence of BMI2 is exposed by the processor via the CPUID feature flags, allowing software to enable optimized code paths conditionally.

Key instructions and capabilities: The extension includes instructions such as PEXT (parallel bits extract) and PDEP (parallel bits deposit), which allow selective extraction or placement of bits based on a mask, as well as MULX, which performs multiplication with explicit destination operands. These enable more efficient algorithms for bit packing, compression, cryptographic primitives, and big-integer arithmetic by reducing the number of instructions and avoiding temporary registers.

Impact and usage: In practice, BMI2 enables compilers and libraries to implement high-performance bit-twiddling routines with smaller code size and lower latency on supporting processors. Software that relies on bit-level manipulation, large integer arithmetic, or performance-critical data processing can benefit from BMI2-enabled builds.

See also: x86 instruction set extensions, BMI1, CPUID feature flags, bit manipulation.