e8620bd7e5e07c025a5e317ebc8c7df95dc63712 - arch/riscv: Add bitrev.h file to support rev8 and brev8

Wed, 06 May 2026 19:52:05 +0200

arch/riscv: Add bitrev.h file to support rev8 and brev8The RISC-V Bit-manipulation Extension for Cryptography (Zbkb) providesthe 'brev8' instruction, which reverses the bits within each byte.Combined with the 'rev8' instruction (from Zbb or Zbkb), which reversesthe byte order of a register, we can efficiently implement 16-bit,32-bit, and (on RV64) 64-bit bit reversal.This is significantly faster than the default software table-lookupimplementation in lib/bitrev.c, as it replaces memory accesses andmultiple arithmetic operations with just two or three hardwareinstructions.Select HAVE_ARCH_BITREVERSE as well as GENERIC_BITREVERSE,and provide to utilize these instructions whenthe Zbkb extension is available at runtime via the alternativesmechanism.[Yury: select the options conditionally on BITREVERSE]Link: https://docs.riscv.org/reference/isa/unpriv/b-st-ext.htmlSuggested-by: David Laight Signed-off-by: Jinjie Ruan Signed-off-by: Yury Norov List of files: /linux/arch/riscv/include/asm/bitrev.h

Changes in bitrev.h

e8620bd7e5e07c025a5e317ebc8c7df95dc63712 - arch/riscv: Add bitrev.h file to support rev8 and brev8