Bit manipulation instructions: Difference between revisions

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{{primary sources|date=August 2025}}

{{Short description|Hardware-level Bit manipulation instructions}}

{{About|the general topic of Instruction set bit manipulation subsets|bit manipulation extensions unique to AMD and Intel|x86 Bit manipulation instruction set}}

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* The x86 instruction core set contains:

** {{code|BSR}} Bit Scan Reverse - Returns bit index of highest set bit in input, effectively backwards count leading zeros, not defined for 0.

** {{code|BSF}} Bit Scan Forward - Returns bit index of lowest set bit in input, effectively backwards count trailing zeros, but not defined for 0.

* [[SSE4]] and the [[X86 Bit manipulation instruction set|BMI]] instruction set extensions contains instructions for:

** Count leading zeros - {{code|lzcnt}}

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* The [[AVX-512#Bitwise ternary logic|AVX-512 ternary]] extension includes a [[Bitwise ternary logic instruction]], {{code|vpternlog}}. Also noteworthy is a conflict detection instruction. [[AVX-512#Conflict detection|<code>VPCONFLICTD</code>]]

* Also present in the AVX/[[AVX-512]] [[GFNI instruction set|GFNI subset]] is bit-matrix affine transformation and its inverse: {{code|GF2P8AFFINEQB}} is effectively an 8x8 bit-matrix multiply in the [[Galois field]] GF(2^8).<ref>{{cite web | title=GF2P8AFFINEQB — Galois Field Affine Transformation | url=https://www.felixcloutier.com/x86/gf2p8affineqb }}</ref>

* AVX-512 BITALG besides AVX-512 version of existing bit manipulation instruction, also added {{code|VPSHUFBITQMB}} which is a bit-level shuffle instruction, that picks bits from one source using indexes in the second source.

* An Intel GNFI technology guide on that AVX/AVX512 GNFI Extension also lists numerous uses including parallel byte-wise set/clear/invert bitmanipulation, 5-bit sign-extension and points out the potential is much greater.<ref name=gfni>{{cite web |title=Galois Field New Instructions (GFNI) Technology Guide |url=https://networkbuilders.intel.com/solutionslibrary/galois-field-new-instructions-gfni-technology-guide |website=networkbuilders.intel.com |language=en}}</ref>

* [[Intel BCD opcodes]]

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=== RISC-V ===

In the standard extensions RISC-V has scalar [[bitwise operations]] including shift and arithmetic shift, but no rotate. The omissions are compensated for with additional extensions.

* [[RISC-V]] Zb* extensions contain a significant number of bit manipulation instructions.<ref>{{cite web | title=Riscv-bitmanip/Bitmanip/Index.adoc at main · riscv/Riscv-bitmanip | website=[[GitHub]] | url=https://github.com/riscv/riscv-bitmanip/blob/main/bitmanip/index.adoc }}</ref> The four groups are broken down into useful categories (the integer subset has min/max, rotate and [[Popcount]] for example), and have very good well-researched justifications for their inclusion and the improvements they bring.<ref>{{cite web | title=Riscv-bitmanip/Bitmanip/Overview.adoc at main · riscv/Riscv-bitmanip | website=[[GitHub]] | url=https://github.com/riscv/riscv-bitmanip/blob/main/bitmanip/overview.adoc }}</ref>

* The RISC-V Vector Extension (RVV) has instructions that qualify as hardware-level bit manipulation, but on Vector masks rather than Scalar registers as is normally the case. For example, a Vector-mask [[Popcount]] is available.<ref>{{cite web | title=Riscv-v-spec/V-spec.adoc at master · riscvarchive/Riscv-v-spec | website=[[GitHub]] | url=https://github.com/riscvarchive/riscv-v-spec/blob/master/v-spec.adoc#15-vector-mask-instructions }}</ref> RVV also has per-element [[bitwise operations]].<ref>{{cite web | title=Riscv-v-spec/V-spec.adoc at master · riscvarchive/Riscv-v-spec | website=[[GitHub]] | url=https://github.com/riscvarchive/riscv-v-spec/blob/master/v-spec.adoc#115-vector-bitwise-logical-instructions }}</ref>

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==== Zilog Z80 ====

* The [[Zilog Z80]] [[Z80 instruction set|instruction set]] includes {{code|BIT}}, {{code|RES}}, and {{code|SET}} instructions. These test, reset, and set individual bits in registers or memory pointed to by HL.<ref>{{Cite book |url=https://www.zilog.com/docs/z80/um0080.pdf#G5.1130345 |title=Z80 Family CPU User Manual |publisher=[[Zilog]] |year=2016 |id=UM008011-0816 |access-date=January 5, 2024 |archive-url=https://web.archive.org/web/20231226131929/http://www.zilog.com/docs/z80/um0080.pdf#G5.1130345 |archive-date=December 26, 2023 |url-status=live}}</ref>

==== MOS 6502 ====

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}}

{{Reflist}}

== Further reading ==

* {{cite thesis |last1=Hilewitz |first1=Yedidya |title=Advanced bit manipulation instructions: Architecture, implementation and applications |date=2008 |publisher=[[Princeton University]] |degree=PhD |url=https://www.proquest.com/openview/0ad3a2474b0691b65b35582fbdb3cf40/1.pdf?pq-origsite=gscholar&cbl=18750}}

** {{cite book |last1=Hilewitz |first1=Yedidya |last2=Lee |first2=Ruby B. |title=Advanced Bit Manipulation Instruction Set Architecture. Technical Report CE-L2006-004 |date=November 2006 |publisher=Princeton University Department of Electrical Engineering |url=https://www.researchgate.net/publication/249884287}}

* {{cite conference |last1=Koppelmann |first1=Bastian |last2=Adelt |first2=Peer |last3=Mueller |first3=Wolfgang |last4=Scheytt |first4=Christoph |conference=2019 29th International Symposium on Power and Timing Modeling, Optimization and Simulation (PATMOS) |title=RISC-V Extensions for Bit Manipulation Instructions |publisher=IEEE |date=2019 |pages=41–48 |isbn=978-1-7281-2103-1 |doi=10.1109/PATMOS.2019.8862170 }}

{{Instruction set extensions}}