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RISC-V Instruction Set Manual, Volume I: RISC-V User-Level ISA , Priv-v1.12 2021/12/03

18 “B” Standard Extension for Bit Manipulation, Version 0.0

This chapter is a placeholder for a future standard extension to provide bit manipulation instructions, including instructions to insert, extract, and test bit fields, and for rotations, funnel shifts, and bit and byte permutations.

Although bit manipulation instructions are very effective in some application domains, particularly when dealing with externally packed data structures, we excluded them from the base ISAs as they are not useful in all domains and can add additional complexity or instruction formats to supply all needed operands.

We anticipate the B extension will be a brownfield encoding within the base 30-bit instruction space.